JPH11330624A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the quantity of light absorbed by a modulator from increasing so as to prevent a photocurrent from increasing, by a method wherein a waveguide structure is composed of a main waveguide which guides laser beams emitted from a semiconductor laser to a modulator, and an auxiliary wave guide which guides a part of laser beams emitted from a semiconductor laser to a section other than the waveguide. SOLUTION: A semiconductor laser 11 which generates laser beams, and field absorption type optical modulator 12 which modulates the laser beams generated by the semiconductor laser 11, are integrated into a semiconductor device 10, and the semiconductor device 10 is equipped with a waveguide structure 13 which guides laser beams. The waveguide structure 13 is composed of a main waveguide 14 and an auxiliary waveguide 15 which ramifies from the main waveguide 14, laser beams generated by the semiconductor laser 11 are guided to the modulator 12 through the main waveguide 14, and a part of laser beams generated by the semiconductor laser 11 are guided to a part other than the modulator 12 through the auxiliary waveguide 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device used as a light source for optical fiber communication, and more particularly to a modulator integrated semiconductor laser device.

[0002]

2. Description of the Related Art Conventionally, a modulator integrated semiconductor laser device has been used as a light source for optical fiber communication. Such a modulator-integrated semiconductor laser device generally has a structure in which a semiconductor laser having an optical diffraction grating and an electroabsorption optical modulator are integrated. The modulator integrated semiconductor laser device used for optical fiber communication generally has the following requirements.

A relaxation oscillation frequency of a modulator integrated semiconductor laser device is higher than at least a frequency of a voltage for driving an electro-absorption optical modulator.

A modulator integrated semiconductor laser device having a narrow spectral line width. Preferably, it is 10 MHz or less.

A current generated due to the light absorption of the electro-absorption optical modulator (hereinafter, referred to as “photocurrent”)
Is small enough not to adversely affect the electric circuit for driving the electro-absorption optical modulator. Preferably, it is 5 mA or less.

The above and the above requirements can be satisfied by increasing the photon density of the semiconductor laser. However, when the photon density is increased, the amount of light incident on the electroabsorption modulator from the semiconductor laser at the same time is increased. Increases, the amount of light absorbed by the electroabsorption modulator increases,
As a result, the photocurrent increases. For this reason, there is an inconvenience that it is difficult to satisfy the above requirements.

Accordingly, the present invention provides a semiconductor device which satisfies all of the above requirements, has a high relaxation oscillation frequency, has a narrow spectral line width, and has a high performance modulator and a semiconductor laser with a small photocurrent. The purpose is to do.

[0008]

In order to achieve the object of the present invention, a semiconductor device according to claim 1 comprises a semiconductor laser for generating a laser beam, a waveguide structure for guiding the generated laser beam, and a waveguide. A modulator that modulates the laser light to be waved, wherein the waveguide structure includes a main waveguide that guides laser light generated from the semiconductor laser to the modulator side, and a laser light generated from the semiconductor laser. And a sub-waveguide that guides a part to a portion other than the modulator.

According to this configuration, a part of the laser light generated from the semiconductor laser is guided along the sub-waveguide to a part other than the modulator. Therefore, even if the photon density inside the semiconductor laser is increased, a part of the laser light is guided to a part other than the modulator, so that the amount of light incident on the modulator can be suppressed, thereby The amount of light absorbed by the modulator can be suppressed to prevent an increase in photocurrent.

According to a second aspect of the present invention, there is provided a semiconductor device according to the first aspect, wherein a light amount of a laser beam generated from a semiconductor laser is monitored in the sub-waveguide. A light detecting element for performing the operation. And, in particular,
According to a third aspect of the present invention, in the semiconductor device, the light detecting element is a photodiode.

According to this configuration, the same operation as the first aspect of the invention is achieved. In addition, the amount of laser light generated from the semiconductor laser can be monitored by the photodetector (photodiode) formed in the sub-waveguide. Thereby, the output of the semiconductor laser can be monitored, and a stable operation can be realized.

[0012]

Embodiments of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a schematic diagram of a semiconductor device 10 according to the first embodiment of the present invention. Referring to FIG. 1, this semiconductor device 10 is used, for example, as a light source for optical fiber communication. The semiconductor device 10 is configured by integrating a semiconductor laser 11 for generating laser light and an electro-absorption optical modulator (hereinafter, referred to as a “modulator 12”) for modulating the generated laser light. The semiconductor device 10 has a waveguide structure 13 for guiding laser light.
It has.

A feature of this embodiment is that the waveguide structure 13 has a main waveguide 14 and a sub-waveguide 15 branched from the main waveguide 14. That is, the laser light generated from the semiconductor laser 11 is guided to the modulator 12 side by the main waveguide 14, and a part of the laser light generated from the semiconductor laser 11 is The feature is that it is guided to a part.

Next, a method of manufacturing the semiconductor device 10 will be described with reference to FIGS. (1) Referring to FIG. 2, the entire surface of n-InP substrate 21 is
An iO ₂ film 22 is formed. This SiO ₂ film 22 is formed by, for example, a sputtering method. Then, the SiO
₂ The central part of the film 22 is removed. The removal operation of the SiO ₂ film 22 can be performed by, for example, wet etching using hydrofluoric acid. As a result, the selective growth mask 22 made of SiO ₂ is formed at both ends of the n-InP substrate 21.

[0015] Thereafter, on the n-InP substrate 21, nI
nP buffer layer 23, n-InGaAsP light confinement layer 2
4, MQW layer 25 in which thin films of InGaAs and InGaAsP are laminated, p-InGaAsP light confinement layer 26, p
-InP first cladding layer 27 and p-InGaAsP
The light guide layers 28 are sequentially laminated. Each of these layers is selectively grown using, for example, the MOCVD method.

In this embodiment, the thickness of each layer is
The n-InP buffer layer 23 is 100 nm, n-InGa
AsP light confinement layer 24 is 50 nm, InGaAs and I
Each film of nGaAsP is 3 to 10 nm, p-InGaAs
The P light confinement layer 26 is 50 nm, the p-InP first cladding layer 27 is 150 nm, and the p-InGaAsP light guide layer 28
Is set to 30 nm.

(2) Referring to FIG. 3, p-InGaAsP
A mask (not shown) is formed on the light guide layer 28 using an interference exposure method. Then, using this mask, p
-The InGaAsP light guide layer 28 is removed by etching. As a result, a diffraction grating 29 made of p-InGaAsP is formed in a portion where the semiconductor laser 11 is formed.

(3) Referring to FIG. 4, p-type
The InP second cladding layer 30 is formed. This p-InP
As the second cladding layer 30, a p-InP layer is selectively grown by using, for example, the MOCVD method. At this time, p-InP
The thickness of the second cladding layer 30 can be set to, for example, 700 nm, whereby the diffraction grating 29 is embedded.

(4) Referring to FIG. 5, next, p-InP
Forming an SiO ₂ film 31 on the upper surface of the second cladding layer 30;
The ridge-type waveguide structure 13 is formed by removing each of the above layers using this as a mask.

Specifically, the SiO ₂ film 31 is made of p-In
A substantially Y-shape is formed on the upper surface of the P second cladding layer 30. Then, the ridge-type waveguide structure 13 is formed by wet etching using, for example, CH ₃ Br. At this time,
Since the SiO ₂ film 31 is formed in a Y-shape, as shown in FIG. 6, the waveguide structure 13 includes a portion where the semiconductor laser 11 is formed and a portion where the modulator 12 is formed when viewed from above. It has a shape branched between.

That is, the waveguide structure 13 is composed of the main waveguide 14
And a sub-waveguide 15 branched therefrom.
Sub-waveguide 15 is formed so as to be retracted from the portion where 2 is formed.

(5) Referring to FIG. 7, a semi-insulating InP layer 31 is formed from this state. This semi-insulating InP layer 31
Is buried by MOCVD, for example.

(6) Referring to FIG. 8, the above SiO ₂ film 31
Is removed, and a p-InP third cladding layer 32 and a p-InGaAs contact layer 33 are sequentially formed on the entire surface. In the present embodiment, the p-InP third cladding layer 32 has a thickness of 2.
5 μm, p-InGaAs contact layer 32 is 10 μm
Can be set to

(7) Referring to FIG. 9, a groove 34 is formed between the modulator 12 and the semiconductor laser 11 in order to electrically separate them. This groove 18 is made of, for example, HC
1 is formed by etching.

(8) Referring to FIG. 10, p-InGaAs
An SiO ₂ insulating film 35 is formed on the entire upper surface of the contact layer 33. This SiO ₂ insulating film 35 is formed by, for example, a sputtering method. Then, an opening for an electrode is provided in a portion where the electrodes of the semiconductor laser 11 and the modulator 12 are formed. This opening is formed by, for example, wet etching with hydrofluoric acid. Cr / A
The u electrodes 36 and 37 are formed by, for example, a sputtering method. Thereafter, Au plating layers 38 and 39 are formed. The thickness of the Au plating layers 38 and 39 is, for example, 2 to 3 μm.
Can be set to Further, the n-InP substrate 21
AuGe / Ni / Ti / Pt / Ti / Pt
After forming the Au electrode 40 by vapor deposition, the Au plating layer 41 is patterned.

Thereafter, the wafer thus formed is cleaved into a bar shape, and the end face of the modulator 12 is coated with low reflection, and the end face of the semiconductor laser is coated with high reflection.

Incidentally, such a semiconductor device 10 has the following properties. First, the relaxation oscillation frequency fr of the semiconductor laser 11 is calculated by using Sp as the photon density.

[0028]

(Equation 1)

There is the following relationship. The spectral line width Δν of the semiconductor laser 11 is:

[0030]

(Equation 2)

There is the following relationship. Therefore, if the photon density Sp can be increased, there is a property that fr can be increased and Δν can be reduced.

Then, the semiconductor device 1 according to the present embodiment
According to 0, the laser light generated from the semiconductor laser 11 is guided to the modulator 12 side along the main waveguide 14 of the waveguide structure 13, and the intensity and phase of the light are modulated in the modulator 12. However, part of this laser light is
Are guided to portions other than the modulator 12 along the axis. That is, a part of the laser light is discarded outside the modulator 12. Therefore, even if the photon density of the semiconductor laser 11 is increased, a part of the laser
By guiding the light to other parts, the amount of light incident on the modulator 12 can be suppressed. This makes it possible to suppress the amount of light absorbed by the modulator 12 and prevent an increase in photocurrent. That is, by increasing the photon density of the semiconductor laser 11, a high relaxation oscillation frequency and a narrow spectral line width can be realized, and the modulator 12 can be favorably driven while suppressing an increase in photocurrent.

Embodiment 2 FIG. Next, a second embodiment of the present invention will be described. FIG. 11 shows Embodiment 2 of the present invention.
FIG.

Referring to FIG. 10, the present embodiment is different from the first embodiment in that the sub-waveguide 15 in the first embodiment is different from the first embodiment.
The difference is that a monitor photodiode 51 as a photodetector is provided above. That is, the present embodiment is characterized in that a waveguide monitor photodiode structure is formed on the sub-waveguide 15. Other structures are the same as in the first embodiment.

The monitor photodiode 51 is formed by forming a waveguide type monitor photodiode structure on the sub-waveguide 15. Therefore,
The structure of the monitor photodiode 51 is the same as the structure where the modulator 12 is formed, and can be formed by the manufacturing process shown in FIGS. However,
Although it is necessary to provide the monitor photodiode 51 with the electrode 52, this electrode 52 can be formed by the process shown in FIG.

The modulator 12 employed in the first embodiment and the present embodiment is an electro-absorption type optical modulator,
By applying a reverse bias voltage to the pn junction, the modulator 12 shifts the absorption light spectrum to the longer wavelength side and absorbs the light generated by the semiconductor laser 11. At this time, a photocurrent is generated. By monitoring this current, the modulator is connected to the monitor photodiode 5.
It can be used as 1.

According to the present embodiment, the same functions and effects as those of semiconductor device 10 according to the first embodiment can be obtained. in addition,
The monitor photodiode 51 allows the semiconductor laser 11
Since the light amount of the laser light generated from can be monitored, the output of the semiconductor laser 11 can be monitored,
There is an advantage that a stable operation can be realized. In addition, in particular, since the monitor photodiode 51 is formed as a photodetector, there is an advantage that the semiconductor device 10 can be easily formed in the same process as the conventional process in the manufacturing process.

[0038]

According to the first aspect of the present invention, a part of the laser light is guided to a portion other than the modulator along the sub-waveguide. The amount of light incident on the container can be suppressed to suppress an increase in photocurrent. In other words, by increasing the photon density of a semiconductor laser, a high relaxation oscillation frequency and a narrow spectral line width are realized, and a high-performance semiconductor device capable of favorably driving a modulator while suppressing an increase in photocurrent. Can be provided.

According to the second aspect of the invention, the same effects as those of the first aspect of the invention can be obtained. In addition, by monitoring the amount of laser light generated from the semiconductor laser by the photodetector photodiode formed in the sub-waveguide, stable operation of the semiconductor laser can be realized, thereby improving the performance of the entire semiconductor device. Can be. In particular, in the invention according to claim 3, since a photodiode is employed as the photodetector, there is an advantage that the photodetector can be easily configured.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a schematic configuration of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 2 (a) is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

FIG. 3 is a cross-sectional view showing a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 3 (a) is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

4A and 4B are cross-sectional views showing a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 4A is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

FIG. 5 is a cross-sectional view showing a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 5 (a) is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

FIG. 6 is a perspective view showing a waveguide structure of the semiconductor device according to the first embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 7 (a) is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

8A and 8B are cross-sectional views illustrating a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 8A is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

FIG. 9 is a cross-sectional view showing a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 9 (a) is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

FIGS. 10A and 10B are cross-sectional views showing a part of the manufacturing process of the semiconductor device according to the first embodiment of the present invention, wherein FIG. 10A is a cross-sectional view as viewed from the front side, and FIG. It is sectional drawing of the state seen from the side surface side.

FIG. 11 is a perspective view schematically showing a schematic configuration of a semiconductor device according to a second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 10 semiconductor device, 11 semiconductor laser, 12 modulator, 13 waveguide structure, 14 main waveguide, 15 sub-waveguide, 50 semiconductor device, 51 photodiode.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI H04B 10/06 10/28 10/02

Claims (3)

[Claims] 1. A semiconductor device including a semiconductor laser that generates laser light, a waveguide structure that guides the generated laser light, and a modulator that modulates the guided laser light, wherein the waveguide structure is A main waveguide for guiding the laser light generated from the semiconductor laser to the modulator side, and a sub-waveguide for guiding a part of the laser light generated from the semiconductor laser to parts other than the modulator. Characteristic semiconductor device. 2. The semiconductor device according to claim 1, wherein a light detecting element for monitoring the amount of laser light generated from the semiconductor laser is formed in the sub-waveguide. . 3. The semiconductor device according to claim 2, wherein said photodetector is a photodiode.