JP2003101125A - Waveguide type optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high-speed response by the reduction of a leakage current and the reduction of the capacity of an element, in a waveguide type optical element equipped with a pn current block layer. SOLUTION: A semiconductor laser region (LD region) 100a equipped with a strip-form waveguide structure and an EA-type light modulator region (EA region) 100b are made, with an isolation region 100c in-between, on a semiconductor substrate 1 consisting of InP or the like. P<-> -type semiconductor layers 23 consisting of InP doped in low concentration with Zn, P<+> -type semiconductor layers 25 consisting of InP doped in high concentration with Zn, and semiconductor layers 27 consisting of InP doped with Si are stacked sequentially and embedded on both sides of this waveguide structure so as to form a current throttling region. Furthermore, in the current throttling region, trench grooves 32 being dug to reach the semiconductor substrate 1 are made.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor device, and more particularly to a waveguide type optical element and a waveguide type optical element module used in a high speed and large capacity optical fiber communication system.

[0002]

2. Description of the Related Art In a waveguide type optical element such as a waveguide type semiconductor light emitting element, a waveguide type light receiving element and a waveguide type optical modulator, a core semiconductor called an active layer provided on a semiconductor substrate and having a large refractive index is used. A laminated structure is formed in which the layers are sandwiched between clad semiconductor layers having a low refractive index. The waveguide type optical device includes an n-type semiconductor layer on an n-type substrate, an active layer provided on the n-type semiconductor layer, and a p-type semiconductor layer provided on the active layer. The waveguide type optical element has a pn junction for the purpose of injecting a current or applying an electric field to the active layer.

Further, in the waveguide type optical element, a stripe-shaped optical waveguide structure is formed in the traveling direction of light in order to control the propagation mode of light. A semiconductor embedding layer having a smaller refractive index than the active layer is buried on both sides of this stripe-shaped semiconductor optical waveguide structure in order to confine light. Further, this semiconductor embedding layer concentrates the current injected into the stripe-shaped semiconductor optical waveguide structure,
Alternatively, it also has a function of intensively applying an electric field. In order to achieve this function, the p-type semiconductor layer 95 and the n-type semiconductor layer 9 are formed in the semiconductor buried layer as shown in FIG.
By embedding 7 around the stripe-shaped semiconductor optical waveguide structure, a structure in which no current flows by utilizing the reverse breakdown voltage of the pn junction, or a semi-insulating semiconductor layer 99 is embedded as shown in FIG. Composed of structure.

In the waveguide type semiconductor light emitting device, a forward bias is applied to the pn junction and a current is injected into the active layer to obtain light emission of a predetermined wavelength. Further, in the waveguide type light receiving element and the optical modulator, the modulated signal light is converted into an electric signal by applying a large electric field to the active layer by biasing the pn junction in the reverse direction, or based on the electric signal. Obtain functions such as optical modulation and optical switching. As described above, in order for the waveguide type optical element to operate its function efficiently, it is necessary to effectively inject a current into the active layer or concentrate an electric field in the active layer. Therefore, it is necessary to form a current constriction structure in which the buried layer buried around the active layer and the active layer are electrically insulated from each other and a current does not flow in the buried layer.

The following structure is used as a current confinement method for preventing a current from flowing through the buried layer. (1) A structure in which a pn current blocking layer for preventing a current from flowing by utilizing the reverse breakdown voltage of the pn junction is embedded (structure shown in FIG. 13). (2) A structure in which a high-resistance semi-insulating semiconductor layer is embedded (structure shown in FIG. 14). In order to increase the resistance of the semiconductor layer,
The buried layer is doped with Fe impurities.

[Problems to be Solved by the Invention]

However, in the waveguide type optical element provided with the current blocking layer utilizing the reverse breakdown voltage of the pn junction in the buried layer of FIG. 13, the electrostatic capacitance of the waveguide type optical element is caused due to the junction capacitance of the buried layer. The capacity is considerably large. Therefore, the response speed of the element is limited by the electrostatic capacity of the element, which makes it difficult to achieve high-speed response. Further, as shown in FIG. 14, when a high-resistance semiconductor layer doped with Fe impurities is used, Fe impurities diffuse into the active layer adjacent to the buried layer, and this Fe impurity causes non-existence in the active layer semiconductor. Since the light emitting center is formed, there is a problem that the device characteristics are deteriorated. Further, in the manufacturing process for forming the high resistance semiconductor layer, since Fe impurities contaminate the growth apparatus, it is necessary to provide the growth apparatus separately from the growth apparatus for forming the optical waveguide structure including the active layer. There is a problem of having to do it. Further, the current confinement method in which the high-resistance semiconductor layer is embedded has a problem that electric insulation is poor and current leakage occurs as compared with the case of using the pn current block layer.

Therefore, an object of the present invention is to provide a waveguide type optical device having a current confinement structure capable of reducing current leakage to buried layers other than the active layer and reducing parasitic capacitance of the device, and improving the device characteristics. I decided to provide it.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, a waveguide type optical element according to a first aspect of the present invention comprises an optical waveguide structure and a plurality of semiconductor layers formed around the optical waveguide structure. The current confinement semiconductor layer is formed, and these are provided on the semiconductor substrate. The optical waveguide structure includes a first semiconductor layer having a first conductivity type, a second semiconductor layer having a refractive index higher than that of the first semiconductor layer, and a second conductivity type different from the first conductivity type. A third semiconductor layer having a mold and having a refractive index smaller than that of the second semiconductor layer is sequentially stacked.

The current confinement semiconductor layer formed around the optical waveguide structure is composed of a plurality of semiconductor layers,
A fourth semiconductor layer doped with a conductivity type impurity at a low concentration, and a fifth semiconductor layer doped with a second conductivity type impurity at a higher concentration than the fourth semiconductor layer on the fourth semiconductor layer. A semiconductor layer and a sixth semiconductor layer doped with an impurity of the first conductivity type are provided on the fifth semiconductor layer.

When the waveguide type optical element according to claim 1 includes a semiconductor optical device which operates by applying a reverse bias to elements such as a waveguide type light receiving element and a waveguide type optical modulator, a current confining semiconductor The depletion layer in the layer region spreads into the fourth semiconductor layer designed to have the lowest impurity concentration, and the impurity concentration of the fourth semiconductor layer is set to a low concentration below a predetermined impurity concentration. By setting the thickness to be equal to or larger than the thickness, the depletion layer capacitance in the current confining semiconductor layer region can be reduced. Since most of the capacitance component of the waveguide type optical element is due to the depletion layer capacitance of the current confinement structure region, the capacitance of the entire element can be effectively reduced, and the response speed of the element can be reduced. Can be improved. As a result, it is possible to realize a waveguide type optical element used in an optical transmission system of high speed and large capacity of 10 Gb / s or more.

Further, in such a waveguide type optical element, the reverse breakdown voltage of the pn junction formed in the current confinement region can sufficiently reduce the current leakage to the current confinement region, and the active optical waveguide structure can be efficiently activated. The electric field can be concentrated on the layer. Further, since the current confinement semiconductor layer can be made of a semiconductor material having a smaller refractive index than the second semiconductor layer which is the active layer of the optical waveguide structure, the guided wave transverse mode of the signal light is stably controlled. A refractive index waveguide is formed, and the device characteristics can be improved.

On the other hand, the waveguide type optical element according to claim 1,
When a waveguide type light emitting device such as a semiconductor laser used by applying a forward bias is included, leak current flowing through the current constriction region can be reduced, and improvement of device performance such as improvement of light emission efficiency is expected. it can. This is because it is possible to suppress both current leaks in two paths that are considered in the current confinement structure region, and for the following reason.

First, on the side surface of the optical waveguide structure mesa,
Since the fourth semiconductor layer in contact with the optical waveguide structure mesa is lightly doped with impurities, the electrical resistance of the fourth semiconductor layer increases. Thereby, the leak current flowing through the fourth semiconductor layer in contact with the optical waveguide structure mesa can be reduced.

Further, in the current confinement region around the optical waveguide structure mesa, the semiconductor substrate having the first conductivity type or the first semiconductor layer laminated thereon and the first conductivity type are The fourth and fifth semiconductor layers having different second conductivity types, the sixth semiconductor layer having the first conductivity type, and the second semiconductor layer grown and formed on the sixth semiconductor layer,
And a cladding layer having a conductivity type of
A p-type thyristor structure is constructed. This thyristor structure also suppresses current leakage into the current confinement region, and current injection into the optical waveguide structure can be concentrated. By increasing the impurity concentration of the fifth semiconductor layer forming a part of the base layer of the thyristor structure in the current confinement region, the current amplification factor of the thyristor with respect to the current injected into the base layer is lowered, The ON voltage of the thyristor element can be increased. Therefore, it is possible to reduce the leak current flowing through the thyristor structure in the current constriction region.

Further, since a current confinement semiconductor layer made of a semiconductor material having a smaller refractive index than the second semiconductor layer is formed around the optical waveguide structure, the refractive index waveguide is formed, so that a signal is formed. The guided wave transverse mode of light is stably controlled.

The semiconductor material forming the current confining semiconductor layer is almost the same as the semiconductor material forming the optical waveguide structure, and the impurities doped in the semiconductor material forming the current confining semiconductor layer are also contained in the optical waveguide. The same impurities as p-type or n-type conductivity type impurities doped in the semiconductor material forming the structure are used. Therefore, there is no deterioration of element characteristics due to diffusion of impurities into the active layer, which is a concern when the current confinement semiconductor layer is made of a semi-insulating semiconductor doped with Fe impurities. Further, since impurities such as Fe impurities which become non-emissive centers are not used, the influence of contamination of the growth device by impurities is small, and the production of the optical waveguide structure including the active layer and the production of the current confinement semiconductor layer are performed by one device. Can be done at.

A waveguide type optical element according to a second aspect is the waveguide type optical element according to the first aspect, wherein the impurity concentration of the first semiconductor layer formed on the semiconductor substrate is higher than the impurity concentration of the semiconductor substrate. Is also lightly doped, and the fourth semiconductor layer and the first semiconductor layer in the current confinement semiconductor layer are in direct contact with each other, and a pn junction is formed at the interface.

When this waveguide type optical element includes a semiconductor optical device such as a waveguide type light receiving element and a waveguide type optical modulation element which is operated by applying a reverse bias, it is reverse biased in the current confining semiconductor layer region. P that works for blocking
The n-junction becomes a pn-junction formed at the interface between the fourth semiconductor layer and the first semiconductor layer of the current confining semiconductor layer. Since the fourth semiconductor layer in the current confinement semiconductor layer is designed to have a low impurity concentration, the depletion layer in the current confinement semiconductor layer region is the same as the fourth semiconductor layer in the current confinement semiconductor layer and the semiconductor. It can extend to both layers in the first semiconductor layer which is lighter doped than the substrate. As a result, the depletion layer capacitance in the current confinement semiconductor layer region can be further reduced.
In order to reduce the depletion layer capacitance more effectively, it is desirable that the impurity concentration of the first semiconductor layer and the impurity concentration of the fourth semiconductor layer be substantially equal. The reason for this is that when a reverse bias is applied to this waveguide type optical element to operate it, the depletion layer in the current confinement semiconductor layer region has almost the same thickness in the two layers of the first semiconductor layer and the fourth semiconductor layer. This is because the thickness of the depletion layer can be maximized. Also,
In order for the depletion layer to spread sufficiently in the first semiconductor layer, it is desirable that the thickness of the first semiconductor layer lightly doped is 0.1 μm or more. Further, in order to prevent an increase in device resistance, the thickness of the first semiconductor layer lightly doped is
It is preferably 1.0 μm or less.

Further, even if this waveguide type optical element includes a waveguide type light emitting element such as a semiconductor laser used by applying a forward bias, the position of the pn reverse junction in the current confining semiconductor layer region is Since it does not change, the leakage current flowing through the current confinement region can likewise be reduced.

According to a third aspect of the present invention, in the waveguide optical element according to the first or second aspect, the impurity concentration of the fourth semiconductor layer in the current confining semiconductor layer region is 2 × 10 ^17. cm ⁻³ or less and the thickness is 0.3
It is characterized by being at least μm.

The optical waveguide element according to claim 4 is the optical waveguide element according to any one of claims 1 to 3, wherein the impurity concentration of the fifth semiconductor layer in the current confining semiconductor layer region is 1 × 10 ^18. It is characterized by being cm ⁻³ or more. If the waveguide type optical element is used in reverse bias, this
This semiconductor layer acts as a large potential barrier and is effective in reducing leak current. Further, even when used in forward bias, the ON voltage of the thyristor structure made of the current confining semiconductor layer can be increased, so that the leak current flowing through this thyristor structure can be reduced.

A waveguide type optical element according to a fifth aspect is the waveguide type optical element according to any one of the first to fourth aspects, in which the optical waveguide structure comprises first to third semiconductor layers. A trench groove reaching the semiconductor substrate is provided in the current confinement semiconductor layer formed of the fourth to sixth semiconductor layers formed around the.

By providing this trench groove in the current confinement semiconductor layer region, unnecessary current confinement semiconductor layer regions can be electrically isolated, and the area of the current confinement semiconductor layer regions is effectively reduced. The capacitance in the current confining semiconductor layer can be reduced. Further, since the electric resistance of the current confinement semiconductor layer region is increased, the leak current flowing through the current confinement semiconductor layer can be further reduced, so that the device characteristics are improved.

A waveguide type optical element according to a sixth aspect is the waveguide type optical element according to the fifth aspect, wherein the distance Lt from the optical waveguide structure end to the trench groove end is 1.0 μm ≦ Lt ≦.
It is characterized by being in the range of 4.0 μm.

A waveguide type optical element according to a seventh aspect is the waveguide type optical element according to any one of the first to sixth aspects, wherein the semiconductor substrate is made of InP and the current confining semiconductor layer. In which the semiconductor material forming
It is characterized by being P.

The waveguide type optical element according to claim 8 is the waveguide type optical element according to any one of claims 1 to 7, wherein the conductivity type of the semiconductor substrate is n type. The conductivity type is n-type, and the second conductivity type is p-type.

A waveguide type optical element according to a ninth aspect is the waveguide type optical element according to any one of the first to eighth aspects, in which electric field absorption for applying a reverse bias to the optical waveguide structure. Type (EA type) optical modulator is included.

A waveguide type optical element according to a tenth aspect is the waveguide type optical element according to any one of the first to eighth aspects, wherein the optical waveguide structure has at least two or more semiconductor optical devices. It is an optical integrated device including the above.

In the waveguide type optical element according to any one of claims 1 to 8, a waveguide type light receiving element and a waveguide type optical modulation element, which are used by applying a reverse bias to the element, and a forward direction opposite to these elements. Different effects are exerted on the waveguide type light emitting element such as a semiconductor laser used by applying a bias, and the respective element characteristics can be improved. Therefore, as the waveguide type optical element according to claim 1, a waveguide type light receiving element and a waveguide type optical modulator which are used by applying a reverse bias and a semiconductor laser which is used by applying a forward bias. It is suitable for use in an optical integrated circuit in which the above are integrated because the effect is further exhibited.

The waveguide type optical element according to claim 11 is devised based on this finding, and in the waveguide type optical element according to claim 10, a semiconductor optical device operating with a forward bias is used. It is characterized in that semiconductor optical devices that operate in reverse bias are integrated.

For example, as a waveguide type optical element according to a tenth aspect, an EA type optical modulator operating with a reverse bias,
There is an optical integrated optical device in which a semiconductor laser used by being biased in the forward direction to operate is integrated. In the integrated optical device including the semiconductor optical devices biased in mutually different directions in the optical waveguide structure as described above, the EA type optical device is obtained by adopting the configuration of the waveguide optical device according to claim 1. The capacitance of the optical modulator region can be reduced, the operation speed of the modulator can be improved, and the leakage current to the current confinement region of the semiconductor laser can be reduced, so that the emission efficiency of the semiconductor laser can be improved.

In such a waveguide type optical integrated device in which two or more semiconductor optical devices are integrated and bias voltages are applied to the respective semiconductor optical devices in mutually different directions, the optical waveguide structure is surrounded. In a single process, the current confining semiconductor layers having the same structure can be embedded at one time, which simplifies the process and further improves the device characteristics.

According to a twelfth aspect of the waveguide type optical element module, the waveguide type optical element according to any one of the first to eleventh aspects is optically coupled to an optical fiber to input or output an optical signal to the outside. It is characterized by making it easy.

An optical communication system according to a thirteenth aspect is characterized by using the waveguide type optical element according to any one of the first to eleventh aspects or the waveguide type optical element module according to the twelfth aspect. In particular, it is preferable to use the above-mentioned waveguide type optical element or the waveguide type optical element module in a high-speed and large-capacity optical fiber communication system of 1 Gb / s or more.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION The structure and operation of various embodiments according to the present invention will be described below with reference to FIGS. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also,
The dimensional ratios in the drawings do not always match those in the description.

(First Embodiment) FIG. 1 is a perspective view showing the structure of a waveguide type optical element according to the first embodiment, and FIG. 2 is a stripe-shaped optical waveguide taken along line II of FIG. 3 to 4 are cross-sectional views taken along a line parallel to the waveguide structure, and FIGS. 3 to 4 are cross-sectional views taken along line II-II and III-III in FIG. 1, respectively. As shown in FIGS. 1 to 4, an optical integrated device 100 as a waveguide type optical device is an integration of an EA type optical modulator and a semiconductor laser (LD). In FIG. 2, a region (hereinafter referred to as an LD region) 100a for a semiconductor laser is formed on the InP semiconductor substrate 1.
A region (hereinafter referred to as EA region) 100b for the EA type optical modulator, and an isolation region 100c for electrically separating the two optical devices. The semiconductor laser is optically coupled to the EA type optical modulator.
FIG. 3 is a cross section of the LD region 100a when cut in a direction orthogonal to the stripe-shaped optical waveguide structure, and FIG. 4 is a cut surface when cut in the direction orthogonal to the striped-shaped optical waveguide structure in the EA region 100b. The cut surface of is shown. 3 and 4, the LD region 100
The a and EA regions 100b have optical waveguide structures 6 and 7 each having a different layered structure in stripes along the same axis, and a current constriction region 8 embedded around the optical waveguide structures.

As shown in FIG. 2, in the optical integrated device 100, in the LD region 100a including the semiconductor laser, a forward bias is applied to the pn junction by the external power supply 37 and a current is injected to cause a laser oscillation operation. I do. on the other hand,
A reverse bias is applied to the EA region 100b including the EA type optical modulator by the external power source 39 in the opposite direction to the LD region, and a high frequency signal from the high frequency power source 38 is superimposed to perform a laser light modulation operation. . When the internal electric field of the EA type optical modulator changes with this high frequency signal, the amount of light absorption for the laser light inside the optical modulator changes, and the laser light is modulated in synchronization with the high frequency signal.

As shown in FIG. 3, in the LD region 100a, the optical waveguide structure 6 formed in a stripe shape is
On the n-type semiconductor substrate 1, an n-type semiconductor clad layer 3c serving as a first semiconductor layer, an i-type semiconductor active layer 4c not intentionally doped with impurities as a second semiconductor layer, and a p-type semiconductor layer as a third semiconductor layer. The first semiconductor multilayer film 10c is formed by sequentially stacking the type semiconductor first cladding layers 5c.

Further, as shown in FIG. 4, the EA area 10
0b, the optical waveguide structure 7 formed in a stripe shape
On the n-type semiconductor substrate 1, an n-type semiconductor clad layer 12c as a first semiconductor layer, an i-type semiconductor active layer 14c not intentionally doped with impurities as a second semiconductor layer,
As the third semiconductor layer, a p-type semiconductor first cladding layer 16c
And 2 are sequentially stacked to form a second semiconductor multilayer film 18c.

As shown in FIGS. 3 and 4, the current confinement region 8 extends over the periphery of the respective optical waveguide structures 6 and 7 formed in stripes of the LD region 100a and the EA region 100b. As a p ⁻ -type semiconductor layer 23 in which a p ^- type impurity is lightly doped,
As a semiconductor layer, ap ⁺ type semiconductor layer 25 in which p type impurities are doped in a relatively high concentration, and an n type semiconductor layer 27 as a sixth semiconductor layer are sequentially stacked and embedded at one time, and a p ⁻ type semiconductor is further formed. The layer 23 is formed so as to contact the side surfaces of the stripe-shaped optical waveguide structures 6 and 7, and the current confinement semiconductor layer 22 is formed.

Further, in FIGS. 2, 3 and 4, the first semiconductor multilayer film 10c in the LD region 100a and the EA region 1 are formed.
The second p-type semiconductor second cladding layer 29 is grown over the entire surface of the second semiconductor multilayer film 18c of 00b and the upper surface of the current confinement semiconductor layer 22 in the current confinement region 8. p
On the surface of the second semiconductor second cladding layer 29, a p-type contact layer 31a for LD and a p-type contact layer for EA type optical modulator are provided.
The mold contact layer 31b is formed. Further, in these p-type contact layers 31a and 31b, the p-type contact layer is removed on the isolation region 100c. Therefore, the p-type contact layer 31a is separated from the p-type contact layer 31b, and the LD is separated by this separation.
One of the electrodes can be electrically separated from the electrode for the EA type optical modulator.

In FIG. 3 and FIG. 4, an optical waveguide structure in which stripe-shaped trench grooves 32 are formed in the current confinement region 8 so as to reach the n-type semiconductor substrate 1 are formed. It is provided substantially parallel to 6 and 7.

Further, the p-type contact semiconductor layer 31a,
An insulator film 33 is formed so as to cover the surfaces of 31b and isolation region 100c and the surface of trench groove 32. However, the insulator film 33 is L
The anode electrode 35a for D is the p-type contact layer 31.
a and the anode electrode 35b for the EA type optical modulator are p
An opening is formed on the surface that contacts the type contact layer 31b, and the anode electrodes 35a and 35b are configured to make ohmic contact with the p type contact layers 31a and 31b, respectively. A cathode electrode 34 is formed on the entire back surface of the n-type semiconductor substrate 1 in ohmic contact with the n-type semiconductor substrate 1.

The n-type semiconductor substrate 1 is an n-type InP doped with S at a concentration of about 2.0 × 10 ¹⁸ cm ^−3.
It is composed of. Each layer forming the first semiconductor multilayer film 10c in the LD region 100a is made of the following semiconductor materials. That is, the n-type semiconductor clad layer 3c is the first
By using InP as the semiconductor material, the concentration of Si as the first conductivity type impurity is about 1.0 × 10 ¹⁸ cm 2.
It is composed of n-type InP doped with ⁻³ and has a layer thickness of about 200 nm. The i-type semiconductor active layer 4c has a second
By using GaInAsP as the semiconductor material of the above, so-called i-type Ga that is not intentionally doped with impurities is used.
It is composed of InAsP and has a layer thickness of about 300 nm. By using InP as the first semiconductor material, the p-type semiconductor first cladding layer 5c has a Zn concentration of about 1.0 × 1 as an impurity of the second conductivity type different from the first conductivity type.
It is composed of p-type InP doped with 0 ¹⁸ cm ⁻³ and has a layer thickness of about 400 nm.

On the other hand, each layer forming the second semiconductor multilayer film 18c in the EA region 100b is made of the following semiconductor materials. That is, the n-type semiconductor clad layer 12c is formed by using InP as the first semiconductor material.
Concentration of Si as a conductivity type impurity is about 2.0 × 10 ¹⁸ c
It is composed of n-type InP doped with m ⁻³ and has a layer thickness of about 200 nm. The i-type semiconductor active layer 14c is
By using GaInAsP as the second semiconductor material, so-called i-type G, in which impurities are not intentionally doped, is used.
It is composed of aInAsP and has a layer thickness of about 300 nm. By using InP as the first semiconductor material, the p-type semiconductor first cladding layer 16c has a Zn concentration of about 1.0 as an impurity of the second conductivity type different from the first conductivity type.
× consists of a doped p-type InP at ^{10 1} 8 ^{cm -3,} with a thickness of about 400 nm.

In the current confinement regions 8 formed on both sides of the stripe-shaped optical waveguide structures 6 and 7, the p ⁻ type semiconductor layer 23, the p ⁺ type semiconductor layer 25 and the n type semiconductor layer 27 are I.
nP semiconductors are used. In the p ⁻ type semiconductor layer 23, the concentration of Zn as the second conductivity type impurity is about 5.0 × 1.
P ⁻ -type I doped at a relatively low concentration of 0 ¹⁶ cm ⁻³
It is composed of nP and has a layer thickness of about 0.5 μm in a flat portion apart from the stripe mesa portion of the optical waveguide structure.

In order to operate the EA type optical modulator,
When a reverse bias is applied to the region 100b, this
The depletion layer in the flow constriction region 8 is composed of the n-type semiconductor substrate 1 and Z
n doped with a low concentration of p⁻Type semiconductor layer 23
Occurs on the surface. Therefore, p ⁻And the thickness of the type semiconductor layer 23
Regarding the impurity concentration, the reverse of that applied to the EA region 100b.
Thickness and impurities that can be depleted by directional bias
Concentration is important.

This p⁻Type semiconductor layer 23 is depleted
Theoretical experiments to determine the thickness and impurity concentration required for
went. In Fig. 12, the reverse voltage of 1V is applied to the EA area 100b.
Energy near current confinement region when bias is applied
Band computer simulation of band diagrams
Show the result. The calculation conditions are almost the same as in this embodiment.
The impurity concentration of each semiconductor layer and the
And thickness, p ⁻Type semiconductor layer 23 thickness and impurities
The calculation was performed using the concentration as a parameter. Each semiconductor layer
The material, impurity concentration and thickness of
become that way. n-type semiconductor substrate 1: 2.0 × 10¹⁸cm^-3, Sn
InP p⁻Type semiconductor layer 23: 5.0 × 10¹⁶cm^-3, 0.
5 μm, Zn-doped InP p⁺Type semiconductor layer 25: 2.0 × 10¹⁸cm^-3, 0.
2 μm, Zn-doped InP n-type semiconductor layer 27: 1.0 × 10¹⁸cm^-3, 0.3
μm, Si-doped InP

[0049] In FIG. 12, the depletion layer, p ^- is spread in the mold semiconductor layer 23, the p ^- type semiconductor layer 23
Are depleted. Therefore, it can be seen that the expected effect can be obtained with the above structure.

[0050] p ^- -type semiconductor layer 23 for a range of thickness and impurity concentration necessary for deplete, more detailed calculation of the result of this p ^- a type semiconductor layer 23 thickness of 0.3μm or more And the impurity concentration is 2 × 10 ¹⁷
It has been found that it is desirable to set it to be cm ⁻³ or less.

Thus, by forming the current confinement region 8 with the structure described above, the depletion layer capacitance of the EA region 100b can be sufficiently reduced, and the operating speed of the EA type optical modulator is improved.

Similarly, in the p ⁺ type semiconductor layer 25, Zn as the second conductivity type impurity has a concentration of about 2.0 × 10 ¹⁸ cm 2.
^-3 , which is composed of p ⁺ -type InP doped to a relatively high concentration, and has a layer thickness of about 0.5 μm in a flat portion away from the stripe mesa portion of the optical waveguide structure. In order for the p ⁺ type semiconductor layer 25 to act as a large barrier height (potential barrier) for blocking the leak current, the impurity concentration of the p ⁺ type semiconductor layer 25 is 1 × 10 ¹⁸ cm ^−3.
It is desirable to do the above. Further, by providing the highly doped p ⁺ type semiconductor layer 25, the LD
Current leakage to the current constriction region in the region 100a can also be suppressed.

The boundary between the p ^-- type semiconductor layer 23 and the p ⁺ -type semiconductor layer 25 does not have to be clear, and the impurity concentration may be gradually changed, or may be changed stepwise. You may comprise.

In the n-type semiconductor layer 27, impurities of the first conductivity type are used.
Concentration of Si as a substance is about 1.0 × 10 ¹⁸cm^-3At Do
Of the optical waveguide structure.
The layer thickness in the flat part away from the stripe mesa is about
Having 0.8 μm.

The p-type semiconductor second clad layer 29 is made of InP as the first semiconductor material, and has a Zn concentration of about 1.5 × 10 ¹⁸ cm 2 as an impurity of the second conductivity type.
It is composed of p-type InP doped with ⁻³ and has a layer thickness of about 1500 nm. LD region 100a and EA
P-type contact semiconductor layer 31a in each region 100b
And 31b are p-type GaInA doped with Zn as a second conductivity type impurity at a concentration of about 1 × 10 ¹⁹ cm ^−3.
s semiconductor and has a layer thickness of about 500 nm.

The cathode electrode 34 is made of AuGe / N.
The AuGe region and the Ni region each have a layer thickness of about 100 nm and about 30 nm, respectively. The anode electrodes 35a and 35b of the LD region 100a and the EA region 100b are made of Ti / Pt / A, respectively.
The thickness of each layer of the Ti region, the Pt region, and the Au region is about 20 nm, about 40 nm, and about 100 n.
m respectively. The insulator film 33 is a nitride film (SiN
And a layer thickness of about 100-200 nm. As the insulator film 33, besides the SiN film, a silicon oxide film (SiO 2 film) and a silicon oxynitride film (SiO 2
An insulating silicon compound film such as N film can also be used.

Next, the manufacturing process of the optical integrated device 100 will be described with reference to FIGS. FIG. 9 shows L
FIG. 10 is a perspective view showing the steps from the formation of the first multilayer film 10 in the D region to the formation of the second multilayer film 18 in the EA region.
From the formation of the stripe-shaped optical waveguide structure to the formation of the current confinement semiconductor layer 22 for the current confinement and the second cladding 2
9 and a perspective view showing the steps up to the formation of the p-type contact layer, and FIG.
It is a perspective view showing the formation of the mold electrode.

First, as shown in FIG.
Metal Vapor Deposition (MOVPE; Metal Orga)
nic Vapor Phase Epitaxy) method
On the surface of the n-type semiconductor substrate 1.
Rad layer 3, i-type semiconductor active layer 4, and p-type semiconductor first layer
The rud layer 5 is formed by sequentially stacking. Group III raw material
Triethylgallium (TEG; Triethyl)
  Gallium) and trimethylindium (TM)
I; Trimethyl Indium), V group
As a raw material arsine (AsH_ThreeArsine) and
Phosphine (Ph _Three; Phospine)
It was Further, as a raw material for the dopant impurities, an n-type semiconductor is used.
For the body, silane (SiH_Four) Can be used, p-type semiconductor
For the body, diethyl zinc (DEZ; Diethyl)
  Zinc) can be used. Flow the above gas at a specified flow
The desired thickness, mixed crystal composition and
Carrier concentration is realized. n-type semiconductor cladding layer 3
The growth temperature of the p-type semiconductor first cladding layer 5 is set appropriately.
However, considering the crystallinity, which layer is
Also, 600 ° C to 750 ° C is preferable.

Next, the LD region 1a on the p-type semiconductor first cladding layer 5 is formed based on the ordinary photolithography technique.
Then, the first mask layer 9 is formed. The first mask layer 9 is S
Although it is composed of an iN film, it is a SiO2 film and a SiON film.
An insulating silicon compound film such as a film can be used.

Subsequently, as shown in FIG. 9B, p is formed on the EA region 1b by using the first mask layer 9 as a mask.
-Type semiconductor first clad layer 5, i-type semiconductor active layer 4, and n-type semiconductor clad layer 3 are reactive ion etching (RIE: Reactive Ion Etching).
Removed by. As a result, the n-type semiconductor clad layer 3a and the i-type semiconductor active layer 4a are formed on the LD region 1a.
And the p-type semiconductor 1st clad layer 5a and the 1st semiconductor multilayer film 10 which consists of these semiconductor films are formed.

Then, as shown in FIG. 9C, the n-type semiconductor clad layer 12 and the i-type semiconductor active layer 1 are formed on the EA region 1b removed by etching by the MOVPE method.
4 and p-type semiconductor first cladding layer 16 are sequentially epitaxially grown. As a result, the second semiconductor multilayer film 18 made of these semiconductor films is formed. At this time, L
Since the first mask layer 9 is provided in the D region 1a, the semiconductor crystal is not grown on the insulating film mask 9. Further, the above-mentioned etching depth and the thicknesses of the n-type semiconductor layer 12, the active layer 14 and the p-type semiconductor layer 16 are set so that the active layer 4a and the active layer 14 can be optically coupled to each other. To be done. Then, the first mask layer 9 is removed.

Then, as shown in FIG.
The optical waveguide structure 20a on the axis from the region to the EA region,
20b is formed. For this formation, the second mask layer having a stripe-shaped pattern along the above-mentioned axis is formed on the optical waveguide forming regions of the first and second semiconductor multilayer films 10 and 18 based on a normal photolithography technique. 21 is formed. This axis is defined perpendicular or parallel to the orientation flat (OF) of the semiconductor wafer. The second mask layer 21 is composed of a SiN film, but the insulating silicon compound film can be used. Also,
In this embodiment, the width of the optical waveguide determined by the stripe pattern formed by the second mask layer 21 is about 2 μm. Next, based on a normal wet etching method, the first semiconductor multilayer film 10 and the second semiconductor multilayer film 18 exposed from the second mask layer 21 are exposed to about 1.8 μm where the n-type semiconductor substrate 1 is exposed. The bromine-dissolved methanol is removed as an etching solution to the depth of. As a result of this etching, a stripe-shaped optical waveguide structure mesa 20 that functions as an optical waveguide is formed.

Then, as shown in FIG. 10B, the second
The ordinary MOVPE method is performed with the mask layer 21 of
P on the n-type semiconductor substrate 1⁻Type semiconductor layer 23, p⁺
-Type semiconductor layer 25 and n-type semiconductor layer 27 are epitaxial
The current confinement is caused by the successive filling by growth.
Current confinement semiconductor layer 22 is formed. At this time p ⁻
The type semiconductor layer 23 has a stripe-shaped optical waveguide structure mesa 2.
It is formed so as to contact the side surface of 0. Also, this current narrow
When the confined semiconductor layer 22 is grown, the second semiconductor layer 22 is formed on the second mask layer 21.
No semiconductor crystals are grown. This allows the stra
The current confinement half is formed only around the ip-shaped optical waveguide structure mesa 20.
The conductor layer 22 is embedded and planarized. After this,
The second mask layer 21 is removed.

Then, using the usual MOVPE method, p
The second type semiconductor second cladding layer 29 and the p-type contact semiconductor layer 31 are sequentially grown over the entire surfaces of the stripe-shaped optical waveguide structure mesa 20 and the current confinement semiconductor layer 22.

Next, in order to form the contact layer 31a for the LD and the contact layer 31b for the EA type optical modulator, based on the ordinary photolithography technique,
A third mask layer is formed on the upper surface of the contact layer 31.
The third mask layer is composed of a SiN film, but the above-mentioned insulating silicon compound film can be used. On the isolation region 100c, a part of the contact film 31 exposed from the third mask layer in a region extending along the direction intersecting the axis of the stripe-shaped optical waveguide structure mesa 20 is formed by a normal wet etching method. And removed to obtain the structure shown in FIG. 10 (c). As a result, the electrode in the LD region and the electrode in the EA region can be electrically separated.

Thereafter, as shown in FIG. 11A, a trench groove is formed in the current confinement region 8. First, the p-type contact semiconductor layers 31a and 31b and the isolation portion 100c are formed based on a normal photolithography technique.
A fourth mask layer is formed on the region where the trench groove 32 is formed. The fourth mask layer is composed of a SiN film, but the above-mentioned insulating silicon compound film can be used.

Next, based on the usual wet etching method,
The p-type contact semiconductor exposed from the fourth mask layer.
Body layers 31a and 31b, p-type semiconductor second cladding layer 29,
And the n-type semiconductor layer 2 constituting the current confinement semiconductor layer 22
7, p⁺Type semiconductor layer 25 and p ⁻The n-type semiconductor layer 23
Etching of HBr system until the semiconductor substrate 1 is exposed
Remove with liquid. Therefore, both sides of the striped mesa
Thus, the trench groove 32 is formed in the current confinement region 8. This
As a result, the trench groove 32 prevents the current confinement region 8 from being blocked.
The required portion is removed, and the capacitance can be reduced.

In the optical integrated device according to the present invention, p
Current confinement semiconductor layer 22 for current confinement composed of ⁻ type semiconductor layer 23, p ⁺ type semiconductor layer 25 and n type semiconductor layer 27
By forming the above structure, the operating speed of the optical integrated device can be increased and the current leakage can be sufficiently prevented. However, by providing the trench groove, the operating speed of the optical integrated device can be further increased. Especially in the EA type optical modulator, the modulation speed is further improved. Further, since the leak current flowing through the current constriction region 8 can be reduced, the characteristics of the integrated device are further improved. In particular, reduction of this leakage current can be expected to improve the luminous efficiency of the LD and operate at high temperatures. Therefore,
By providing the trench groove, the effect of the optical integrated device of the present invention is further exerted, which is suitable as the structure of the optical integrated device.

In order to more effectively reduce the capacitance of the current confinement region 8 and reduce the leak current by providing the trench groove 32, the stripe-shaped optical waveguide structure mesa 20 to the trench groove 32 are used. It is better to keep the distance of as small as possible. On the other hand, the i-type semiconductor active layer 4c,
In order to confine light in 14c and stabilize the transverse mode of the optical waveguide, the side surface of the stripe-shaped optical waveguide structure mesa 20 is made of a material having a refractive index lower than that of the semiconductor material forming the i-type semiconductor active layers 4c and 14c. The width may be 1 μm or more from the side surface of the optical waveguide. Therefore, the distance L from the stripe-shaped optical waveguide structure mesa 20 to the trench groove 32 is L.
It is desirable that t is 1 μm to 4.0 μm. In this example, Lt was 3 μm.

Next, the passivation insulator layer 33 is formed by a conventional plasma-enhanced chemical vapor deposition (CDV) method.
It is formed on each exposed surface of the p-type contact semiconductor layers 31a and 31b, the isolation region 100c, and the trench groove 32 based on the 1 Vapor Deposition method. Passivation insulator layer 33
Is composed of a SiN film, but the above insulating silicon compound film can be used.

Further, a fifth mask layer having a predetermined pattern is formed on the surface of the passivation insulator layer 33 based on the ordinary photolithography technique, and the passivation insulator layer 33 exposed from the fifth mask layer is formed. Remove the inner area. Although not shown in the figure, this removal forms contact window openings for making ohmic contact with the anode electrodes 35a, 35b on the p-type contact semiconductor layers 31a, 31b. Next, an ordinary negative resist is applied, and a sixth pattern of a predetermined pattern is formed on the surface of the negative resist based on the ordinary photolithography technique.
And forming a p-type electrode film on a predetermined region of the window opening of the passivation insulator layer 33 and the p-type contact semiconductor layer 31 exposed from the sixth mask layer based on a normal vacuum deposition method. To form. After that, the metal deposited in the regions other than the regions where the anode electrodes 35a and 35b are formed is removed at the same time when the resist is removed by the normal lift-off method, and is electrically insulated from the LD region 100a and the EA region 100b. Anode electrode pattern 3
5a and 35b are formed.

Next, in order to separate the plurality of optical integrated devices formed on the n-type semiconductor substrate 1 by cleavage, n
The back surface of the mold semiconductor substrate 1 is thinned to about 100 μm by a normal polishing process. After that, the cathode electrode 34 is formed on the entire back surface of the n-type semiconductor substrate 1 based on a normal vacuum deposition method, and the optical integrated device 10 shown in FIG.
0 is completed.

In such a manufacturing process, the semiconductor material forming the current confinement semiconductor layer 22 for the current confinement is a stripe including the active layers 4c and 14c in the LD region and the EA region shown in FIGS. Impurities that can be made substantially the same as the semiconductor material forming the optical waveguide structures 6 and 7 and that are doped into the semiconductor material forming the current confining semiconductor layer 22 also form the optical waveguide structures 6 and 7. The same impurities as p-type or n-type conductivity type impurities doped in the semiconductor material are used. Therefore, there is no deterioration in device characteristics due to diffusion of impurities into the active layer, which is a concern in the structure in which the current confinement region is formed of a semi-insulating semiconductor layer doped with Fe impurities. Further, since impurities such as Fe impurities which become non-emissive centers are not used, the influence of contamination of the growth device by impurities is small, and the production of the optical waveguide structure including the active layer and the production of the current confinement semiconductor layer are performed by one device. Can be done at.

Next, the operation of the optical integrated device 100 will be described. In this optical integrated device 100, a reverse bias is applied in order to operate the EA type optical modulator which is the first semiconductor optical device. In this state, in the current confinement region 8 of the EA region 100b, p
Since the type semiconductor layer is separated into two layers, the p ⁻ type semiconductor layer 23 that is lightly doped and the p ⁺ type semiconductor layer 25 that is heavily doped, the depletion layer is the n-type semiconductor substrate 1.
And the p ⁻ type semiconductor layer 23 spread to the interface, and the p ⁻ type semiconductor layer 23 is depleted. Therefore, the capacitance C _BL of the current confinement region 8 is determined by the depletion layer capacitance proportional to the carrier concentration of the p ⁻ type semiconductor layer 23. The p ^- impurity concentration type semiconductor layer 23 by a low concentration of 2 × ^{10 1} 7 ^{cm -3} or less, the capacitance of the EA region 100b C
It is possible to reduce the electrostatic capacitance C _BL of the current constriction region 8 that occupies most of the component of _EA . Since the operating speed of the EA type optical modulator is determined by the electrostatic capacitance C _EA of the EA region 100b, the operating speed of the EA type optical modulator is reduced by reducing the electrostatic capacitance C _BL of the current constriction region 8. Can be improved. Actually, as a result of performing a modulation experiment using the optical integrated device 100 of the first embodiment shown in FIG. 1, good modulation characteristics were obtained even at high speed modulation of 10 Gb / s.

In addition, the current confinement region 8 in the EA region 100b
In the p-type semiconductor layer separated into two layers, the highly-doped p ⁺ -type semiconductor layer 25 functions as a large barrier height (potential barrier) for blocking the leak current, so that the current confinement region 8 is formed. Current leakage to the
An electric field can be effectively applied to the stripe-shaped optical waveguide structure 7 including the EA type optical modulator.

On the other hand, in the LD region 100a, in order to operate the semiconductor laser which is the second semiconductor optical device,
Forward bias is applied. At this time, since the semiconductor laser is used only for the purpose of emitting laser light having a single wavelength, it is used in direct current (DC) operation,
The modulated electrical signal is not superimposed.

A semiconductor laser is formed in the LD region 100a.
Effective current to stripe optical waveguide structure 6 including
To concentrate and reduce the leakage current to the current confinement region 8.
Is important, but in the present embodiment, there are the following two effects.
Leakage current to the current confinement region 8 can be reduced.
It (1) Striped optical waveguide structure including a semiconductor laser
6 in contact with 6 mesa 20a⁻Impurities in the semiconductor layer 23
By doping to a low concentration, p⁻Of the type semiconductor layer 23
Due to the increased electrical resistance, stripe-shaped light
Mesa 20a to p of the waveguide structure 6⁻Through the type semiconductor layer 23
Leakage current can be reduced. (2) In the current confinement region 8, the n-type semiconductor substrate 1-p
⁻Type semiconductor layer 23 / p ⁺Type semiconductor layer 25-n type semiconductor layer
Npnp comprising 27-p type semiconductor second cladding layer 29
A die thyristor structure is formed. This thyristor structure
In construction, p ⁻Type semiconductor layer 23 / p⁺Type semiconductor layer 25
The p-type semiconductor layer composed of is used as the base layer of the thyristor element.
Functioning. The base layer is heavily doped with p
⁺By providing the semiconductor layer 25 of the type,
The current amplification factor of the thyristor element with respect to the input current can be reduced.
Therefore, the ON voltage of the thyristor can be increased.
Therefore, in this current confinement region, the n-type semiconductor substrate is
Board 1-p⁻Type semiconductor layer 23 / p⁺Type semiconductor layer 25-n type
Through the semiconductor layer 27-p-type semiconductor second cladding layer 29
The leak current flowing can be reduced.

Therefore, in the LD region 100a, the leakage current to the current confinement region can be reduced, so that the emission efficiency of the semiconductor laser can be improved, the threshold current and the operating current can be reduced, and the high temperature operation can be performed. Become.

As described above, in the optical integrated device 100 in which the EA type optical modulator and the semiconductor laser are integrated, as compared with the conventional optical integrated device as shown in FIG.
00b and LD region 100a are both current confinement regions 8
It is possible to reduce the leak current flowing in the. In addition, the EA area 10
At 0b, the capacitance is reduced to 10 Gb.
Even during high-speed modulation of / s, good modulation characteristics can be obtained and element characteristics can be improved.

(Second Embodiment) Next, a second embodiment of the waveguide type optical element according to the present invention will be described. Second
As the waveguide type optical element according to the embodiment of the
50 is a distributed feedback semiconductor laser (DFB-LD) and EA
Integrated optical modulator. FIG. 5 is a sectional view of the optical integrated device 150 taken along the stripe direction of the optical waveguide structure. The integrated optical device 150 includes a region (hereinafter referred to as a DFB-LD region) 150a including a distributed feedback semiconductor laser and a region (hereinafter referred to as “E”) including an EA type optical modulator.
150b), and an isolation region 150 for electrically insulating the two optical devices.
with c. The semiconductor layer and the structure shown in FIG. 5 are formed in substantially the same manner as the manufacturing process shown in the first embodiment.

The DFB-LD region 150a includes the Si-doped InP layer 41, the n-type GaInAsP-SCH layer 43, and G.
aInAsP / GaInAsP multiple quantum well structure layer 4
5, p-type GaInAsP-SCH layer 47, p-type InP first cladding layer 49, p-type InP second cladding layer 29, and p-type GaInAs contact layer 31a. These layers are sequentially arranged on the InP semiconductor substrate 1. Further, the DFB-LD region 150a includes an electrode 35a provided so as to give a potential to the anode, and an electrode 34 provided so as to give a potential to the cathode.
The diffraction grating 6 is formed on the P-type GaInAsP-SCH film 47.
1 is formed. The diffraction grating is Si-doped In
It may be formed on the P layer 41.

The EA region 150b includes the Si-doped InP layer 51, the n-type GaInAsP-SCH layer 53, and GaInA.
sP / GaInAsP multiple quantum well structure layer 55, p-type G
aInAsP-SCH layer 57, p-type InP first cladding layer 59, p-type InP second cladding layer 29, and p-type Ga
The InAs contact layer 31b is provided.

A p ^-- type InP semiconductor layer 23, ap ⁺ -type InP semiconductor layer 25, and an n-type InP semiconductor layer 27 are formed on both sides of each stripe-shaped optical waveguide structure over the DFB-LD region 150a and the EA region 150b. It is buried by epitaxial growth to form a current confinement region.

Further, the EA region 150b includes an electrode 35b provided so as to give a potential to the anode, and an electrode 34 provided so as to give a potential to the cathode.

On the other hand, the DFB-LD region 150a includes an electrode 35a provided so as to give a potential to the anode, and an electrode 34 provided so as to give a potential to the cathode.

Also in the second embodiment in which the EA type optical modulator and the DFB-LD are integrated, as in the first embodiment, compared with the conventional optical integrated device as shown in FIG. , EA region 150b and DFB-LD region 150a
In both cases, the leak current flowing in the current constriction region can be reduced. Further, in the EA region 150b, since the electrostatic capacity is reduced, even at the time of high speed modulation of 10 Gb / s,
Good modulation characteristics can be obtained, and device characteristics can be improved.

(Third Embodiment) Next, a third embodiment of the waveguide type optical element according to the present invention will be described. Figure 6
As shown in FIG.
Are configured almost in the same manner as the optical integrated device 100 of the first embodiment. However, the optical integrated device 200 is
It is an optical integrated device in which a waveguide type light receiving element and a semiconductor laser are integrated.

The structure of the optical integrated device 200 is almost the same as that of the optical integrated device of the first embodiment, but the connection method with an external circuit is different.

Similar to the optical integrated device of the first embodiment described above, a forward bias is applied to the pn junction in the LD region 200a including the semiconductor laser and a current is injected to perform a laser oscillation operation and receive light. Element area (hereinafter PD area)
On the contrary, a reverse bias is applied to 200b to perform the operation of receiving and detecting laser light.
However, as shown in FIG. 6, an external load circuit 63 is connected to the PD region in order to take out an electric signal accompanying the photoelectric conversion to the outside.

In the stripe-shaped optical waveguide structure of the PD region 200b, the second semiconductor multilayer film composed of the Si-doped InP layer 74, the i-type GaInAsP active layer 75, and the p-type InP first cladding layer 76 is LD region 2
The striped optical waveguide structure of 00a may be formed in the same manner as the first semiconductor multilayer film including the Si-doped InP layer 64, the i-type GaInAsP active layer 65, and the p-type InP first cladding layer 66. At this time, this semiconductor multilayer film is formed by one-time multilayer epitaxial growth.

LD region 200a and PD region 200b
The p ⁻ -type InP semiconductor layer 23, the p ⁺ -type InP semiconductor layer 25, and the n-type InP semiconductor layer 27 are buried by epitaxial growth on both sides of each stripe-shaped optical waveguide structure to form a current constriction region. There is.

In the third embodiment in which the waveguide type light receiving element and the semiconductor laser are integrated, as in the first embodiment, as compared with the conventional optical integrated element as shown in FIG. Both the PD region 200b and the LD region 200a,
The leak current flowing in the current constriction region can be reduced. Also,
In the PD region 200b, the response speed of the PD element is improved by reducing the capacitance.

(Fourth Embodiment) Next, a fourth embodiment of the waveguide type optical element according to the present invention will be described. Figure 7
As shown in FIG. 4, in the EA type optical modulator device 300 as a waveguide type optical element, a single EA type optical modulator is formed in the optical waveguide structure formed in a stripe shape, and a current constriction region is formed in the vicinity of n. It is formed and formed on the mold semiconductor substrate 1.

The EA type optical modulator device 300 includes the Si-doped InP layer 83 and the n-type GaInAsP-SCH layer 8.
4, GaInAsP / GaInAsP multiple quantum well structure layer 85, p-type GaInAsP-SCH layer 86, p-type In
P first clad layer 87, p-type InP second clad layer 29
And a p-type GaInAs contact layer 31.

The p ⁻ type InP semiconductor layer 23 and p ⁺ are provided around the stripe-shaped optical waveguide structure including the EA type optical modulator.
The type InP semiconductor layer 25 and the n-type InP semiconductor layer 27 are buried by growth to form a current confinement region.

Further, the EA type optical modulator device 300 is
An electrode 35 provided so as to give a potential to the anode, and an electrode 34 provided so as to give a potential to the cathode
Equipped with.

Also in the EA type optical modulator device 300, as compared with the conventional EA type modulator device, the leakage current flowing in the current confinement region can be reduced and the capacitance can be reduced, so that 10 Gb / s can be obtained. Even at the time of high speed modulation, good modulation characteristics can be obtained, and the element characteristics can be improved.

(Fifth Embodiment) Next, a fifth embodiment of the waveguide type optical element according to the present invention will be described. Figure 8
As shown in FIG. 5, in the EA type optical modulator device 400 as a waveguide type optical element, a single EA type optical modulator is formed in a stripe-shaped optical waveguide structure, and a current constriction region is formed around it. Has been configured.

In the EA type optical modulator device 400,
The optical waveguide structure formed in a stripe shape has an n-type InP structure.
On the semiconductor substrate 1, an n-type InP semiconductor clad layer 112 as a first semiconductor layer, an i-type GaInAsP semiconductor active layer 114 not intentionally doped with impurities as a second semiconductor layer, and a p-type semiconductor layer as a third semiconductor layer. The first InP semiconductor first cladding layer 116 is sequentially stacked.
The n-type InP semiconductor cladding layer 112 is doped with Si as an impurity at a relatively low concentration of about 2 × 10 ¹⁷ cm ⁻³ , and its layer thickness is about 0.3 μm. In addition, i-type GaI
The thickness of the nAsP semiconductor active layer 114 is about 300 nm, p
The impurity concentration and the thickness of the first InP semiconductor first cladding layer 116 are about 1.0 × 10 ¹⁸ cm ⁻³ (impurity:
Zn) and about 400 nm.

A p ⁻ type InP semiconductor layer 23 and p ⁺ are provided around the stripe optical waveguide structure including the EA type optical modulator.
The type InP semiconductor layer 25 and the n-type InP semiconductor layer 27 are
It is sequentially buried by epitaxial growth to form a current confinement region. In particular, the p ⁻ type InP semiconductor layer 23 is
It is formed so as to contact the side surface of the stripe-shaped optical waveguide structure mesa.

The stripe-shaped optical waveguide structure is composed of n-type In
The p-type InP semiconductor clad layer 112 and the p ⁻ -type InP semiconductor clad layer 112 of the current constriction layer formed by etching until the P semiconductor clad layer 112 is exposed are formed into a mesa shape and then formed by burying growth. Form a bond. The thickness of the first semiconductor layer flat portion in the current confinement region after the mesa formation is 0.2 μm. p ^- type In
The impurity concentration of the P semiconductor layer 23 is about 2.0 × 10 ¹⁷ cm
^-3 , the thickness is about 0.5 μm. Further, the EA type optical modulator device 400 includes an electrode 35 provided so as to give a potential to the anode, and an electrode 34 provided so as to give a potential to the cathode.

When a reverse bias is applied to the EA type optical modulator 400 to operate it, the above-mentioned p
^The pn junction formed at the interface between the ⁻ type InP semiconductor layer 23 and the n type InP semiconductor cladding layer 112 is reverse biased. As a result, current leakage to the periphery of the stripe-shaped optical waveguide structure is prevented, and the electric field is concentrated on the optical waveguide structure including the EA type optical modulator. At this time, p ⁻ type InP
The semiconductor layer 23 and the n-type InP semiconductor clad layer 112, both the opposite conductivity type impurity of about 2 × ^{10 1} 7 cm
^-3 , the depletion layer at the time of reverse bias is similar to the p ⁻ -type InP semiconductor layer 23 and the n-type InP semiconductor clad layer 112, since the depletion layer has a thickness of 0.1 μm or more. Since the thickness of the depletion layer can be increased, the junction capacitance in the current constriction region can be reduced more effectively. Therefore, even during high-speed modulation of 10 Gb / s, good modulation characteristics can be obtained and the element characteristics can be improved.

(Sixth Embodiment) Next, a sixth embodiment of the waveguide type optical element according to the present invention will be described. A semiconductor laser as a waveguide type optical element is configured substantially the same as the waveguide type optical element of the fourth embodiment. However, a single semiconductor laser element is formed in the optical waveguide structure formed in a stripe shape, and a current confinement region is formed in the periphery of the single semiconductor laser element.
It is formed and formed on the mold semiconductor substrate 1.

Also in the semiconductor laser according to the sixth embodiment, the leakage current flowing in the current confinement region can be reduced as compared with the conventional buried type semiconductor laser.
The device characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a waveguide type optical element according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a structure of the waveguide type optical element according to the first embodiment of the present invention, taken along line I-I in FIG.

FIG. 3 is a cross-sectional view showing a structure taken along line II-II of FIG. 1 in the waveguide type optical element according to the first embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a structure of the waveguide type optical device according to the first embodiment of the present invention, taken along line III-III in FIG. 1.

FIG. 5 is a sectional view showing the structure of a waveguide type optical element according to a second embodiment of the present invention.

FIG. 6 is a sectional view showing a structure of a waveguide type optical element according to a third embodiment of the present invention.

FIG. 7 is a sectional view showing a structure of a waveguide type optical device according to a fourth embodiment of the present invention.

FIG. 8 is a sectional view showing a structure of a waveguide type optical device according to a fifth embodiment of the present invention.

9A to 9C are process diagrams sequentially showing a manufacturing process in the waveguide type optical element of FIG.

FIG. 10 is a process chart sequentially showing the manufacturing process subsequent to FIG. 9 in the waveguide type optical device of FIG.

11 is a process diagram sequentially showing the manufacturing process subsequent to FIG. 10 in the waveguide type optical device of FIG. 1. FIG.

FIG. 12 is a diagram showing an energy band diagram of a current confinement region of a waveguide type optical element.

FIG. 13 is a cross-sectional view showing the structure of a waveguide type optical element of a first conventional example.

FIG. 14 is a cross-sectional view showing a structure of a second conventional waveguide type optical element.

[Explanation of symbols]

100, 150, 200, 300, 400 ... Waveguide type optical element 1 ... Semiconductor substrates 3c, 12c ... N-type semiconductor clad layers 4c, 14c ... i-type semiconductor active layers 5c, 16c ... P-type first semiconductor clad layer 23 ... p ^-- type buried layer 25 ... p ⁺ type buried layer 27 ... n type buried layer 29 ... p type second semiconductor cladding layers 31a, 31b ... p type contact layer 32 ... trench groove 33 ... insulating film 34 ... cathode electrodes 35a, 35b. ... Anode electrode

Continued front page    F-term (reference) 2H079 AA02 AA13 BA01 CA04 DA16                       DA25 EA07 EA08 HA15 KA18                 5F073 AA09 AA11 AA22 AA64 BA02                       CA12 CB02 EA14 EA23

Claims (13)

[Claims] 1. A semiconductor substrate having a first conductivity type, a first semiconductor layer having a first conductivity type on the semiconductor substrate, and a second semiconductor layer having a refractive index larger than that of the first semiconductor layer. And a third semiconductor layer having a second conductivity type different from the first conductivity type and having a refractive index smaller than that of the second semiconductor layer are sequentially stacked. A buried-structured waveguide type optical device in which a current confinement semiconductor layer is embedded around the structure, wherein the current confinement semiconductor layer is lightly doped with the second conductivity type impurity. A layer, a fifth semiconductor layer on which the impurity of the second conductivity type is doped at a higher concentration than the fourth semiconductor layer, a layer on the fourth semiconductor layer, and a layer on the fifth semiconductor layer And a sixth semiconductor layer doped with impurities of the first conductivity type. Waveguide type optical element. 2. The impurity concentration of the first semiconductor layer is doped to be lower than the impurity concentration of the semiconductor substrate, and the fourth semiconductor layer and the first semiconductor layer in the current confining semiconductor layer. The waveguide type optical element according to claim 1, wherein and are in direct contact with each other. 3. The current confinement semiconductor layer, wherein the impurity concentration of the fourth semiconductor layer is 2 × 10 ¹⁷ cm ⁻³ or less and the thickness thereof is 0.3 μm or more. Alternatively, the waveguide type optical element according to claim 2. 4. The current confinement semiconductor layer according to claim 1, wherein the impurity concentration of the fifth semiconductor layer is 1 × 10 ¹⁸ cm ⁻³ or more. Waveguide optical device. 5. A trench groove reaching the semiconductor substrate is provided in the current confinement semiconductor layer composed of the fourth to sixth semiconductor layers. The waveguide type optical element described. 6. The waveguide type optical device according to claim 5, wherein a distance Lt from the end of the optical waveguide structure to the end of the trench groove is in a range of 1.0 μm ≦ Lt ≦ 4.0 μm. 7. The waveguide according to claim 1, wherein the material of the semiconductor substrate is InP, and the material forming the current confining semiconductor layer is InP which is the same as that of the semiconductor substrate. Type optical element. 8. The waveguide type optical device according to claim 1, wherein the first conductivity type is n-type and the second conductivity type is p-type. 9. The waveguide type optical device according to claim 1, wherein the optical waveguide structure includes an electro-absorption (EA type) optical modulator for applying a reverse bias. 10. The waveguide type optical element according to claim 1, wherein the optical waveguide structure is an optical integrated element including at least two or more semiconductor optical devices. 11. The waveguide type optical element according to claim 10, wherein a semiconductor optical device operating with a forward bias and a semiconductor optical device operating with a reverse bias are integrated in the integrated optical element. 12. A waveguide type optical element module, wherein the waveguide type optical element according to claim 1 is optically coupled to an optical fiber. 13. An optical communication system using the waveguide type optical element according to any one of claims 1 to 11 or the waveguide type optical element module according to claim 12.