KR100265858B1 - Wavelength division multiplexing device with monolithically integrated semiconductor laser and photodiode - Google Patents

Abstract

PURPOSE: A WDM(Wave Division Multiplexing) device for integrating semiconductor laser and photodetector on a single chip is provided to miniaturize the device and improve the transmittance by integrating on a single semiconductor laser for optical data transmission and a photodetector for optical data receiving. CONSTITUTION: The WDM device includes structures of a semiconductor laser(1) and a photodetector(2) both formed on an n-type lnP substrate(7). The semiconductor laser(1) includes an n-type lnP buffer layer(8), an undoped lnGaAsP active layer(99), a p-type lnP buffer layer(17), a p-type lnP clad layer(10), and a p-type lnGaAsP resistant contact layer(11). The photodetector(2) includes a p-type lnGaAsP resistant contact layer(11), an undoped lnP etching stop layer(12), an undoped lnGaAs photo-absorption layer(13) and an n-type lnGaAsP resistant contact layer(14). Here, the laser(1) and photodetector(2) shares a p-type lnGaAsP resistant layer(11) and forms an NPN structure with the n-type lnGaAsP resistant contact layer(14), the p-type lnGaAsP resistant contact layer(11) and the n-type substrate(7).

Description

Wavelength Division Multiplexing with Integrated Semiconductor Laser and Photodetector on a Single Chip

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical device, and more particularly, to an element for wavelength division bidirectional optical communication and a method for manufacturing the same, which simultaneously transmit signals through a single optical fiber using light for transmission and reception.

In general, one of the most important elements in wavelength division multiplexing bidirectional optical communication using a single optical fiber to simultaneously transmit and receive optical signals is a wavelength division multiplexed optical transmission / reception module.

The wavelength division multiplexing optical transmission / reception module includes a wavelength division multiplexing element, a semiconductor laser, and a photodetector element using an optical waveguide that divides one optical path into two different paths depending on the wavelength. In this wavelength division multiplexing device, one common optical waveguide portion is optically coupled to an optical fiber, and two branched optical waveguides are configured to optically couple with a semiconductor laser or a photodetector. The light is optically coupled with the wavelength division multiplexing element and the light travels along the optical waveguide. The light is optically coupled to the optical waveguide, while the light of the receiving wavelength input along the optical fiber is combined and traveled in a common optical waveguide. In the wavelength selection path of the multiplexing device, the optical waveguide travels along the path of the photodetector and is optically coupled to the photodetector to detect a signal.

In the conventional wavelength division multiplexing bidirectional optical communication module, a wavelength division multiplexing device, a semiconductor laser, a photodetector, etc. are fabricated as separate devices and optically integrated in a hybrid form together with an optical fiber. That is, the wavelength division multiplexing element is aligned and fixed so that the semiconductor laser and the photodetector element and two branched optical waveguides are optically aligned, and the common optical waveguide portion of the wavelength division multiplexing element is fixed to be aligned with the optical fiber and manufactured as a module. will be. At this time, the wavelength division multiplexing device is mainly used to change the path according to the wavelength of the light by using the optical waveguide or to change the path of the light according to the wavelength by using the optical branch waveguide and the wavelength selection filter at the same time.

However, according to the wavelength division bidirectional optical communication module, three kinds of optical devices must be manufactured separately, and each of these photonic elements requires a separate precise optical alignment and fixing process, which increases the manufacturing cost of the module. The disadvantage is that the module is difficult to manufacture. In addition, the optical path from semiconductor laser to optical fiber or from optical fiber to photodetector has two or more inter-element optical coupling points and one optical branch point, respectively, which greatly increases the overall insertion loss. This will deteriorate both the light output and the sensitivity of the received light.

Accordingly, in order to solve the disadvantage of the wavelength division bidirectional optical communication module, a wavelength division multiplexing device, a semiconductor laser, and a photodetector device using an optical waveguide are fabricated on a same chip on the same semiconductor substrate. Such a wavelength division bidirectional optical communication module has many advantages, such as a large number of optical components, a large number of optical coupling points, and an increase in assembly cost and deterioration due to them. Since the three kinds of optical devices having the process of fabrication and fabrication must be integrated in a single chip through the same process, the structure and fabrication process becomes very complicated and it is difficult to optimize the structure so that each device has the maximum characteristics. There is a disadvantage in that deterioration of the characteristics cannot be avoided.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems described above. In the wavelength division multiplexed optical communication in which transmission and reception optical signals are simultaneously transmitted using a single optical fiber, a semiconductor laser for transmitting light and a long wavelength that emit light having a short wavelength are long. It is an object of the present invention to provide a wavelength division bidirectional optical communication device and a method of manufacturing the same, which are implemented by integrating a photodetector device for receiving light of a wavelength into a single chip on the same semiconductor substrate.

1 is a plan view of a wavelength division multiplexing device in which a semiconductor laser and a photodetector are integrated in a single chip according to the present invention.

2 is a cross-sectional view taken along line A-A 'of a wavelength division multiplexing device in which a semiconductor laser and a photodetector are integrated in a single chip according to the present invention;

3A to 3G are cross-sectional views illustrating a method of forming a wavelength division multiplexing device according to the present invention.

4 is a cross-sectional view of a semiconductor laser and a photodetector combining a wavelength division multiplexing device in which a single chip is integrated with an optical fiber;

* Explanation of symbols on the main parts of the drawing

1 semiconductor laser region 2 photodetector region

3: P-type common electrode 4: N-type electrode of photodetector

5: nitride film 6: N-type electrode of semiconductor laser

7: N-type InP substrate 8: N-type InP buffer layer

9: undoped InGaAsP active layer

10: P type InP cladding layer

11: P-type InGaAsP resistive contact layer

12: undoped InP etch stop layer

13: undoped InGaAs light absorption layer

14: N-type InGaAsP resistive contact layer

15: wavelength emitted from a semiconductor laser

16: wavelength incident on the photodetector

17: P-type InP buffer layer 18: etching mask

19: P type InP current blocking layer of semiconductor laser

20: N-type InP current blocking layer of semiconductor laser

21: P type InP current blocking layer of semiconductor laser

22 silicon substrate 23 V-groove

24: metal reflective film 25: optical fiber

26: fiber core

In order to achieve the above object, the wavelength division bidirectional optical communication device of the present invention, the first conductive semiconductor substrate; A semiconductor laser including a first conductive buffer layer, an active layer, a second conductive buffer layer, and a second conductive wavelength filter layer positioned on the semiconductor substrate; A photodetector comprising an etch stop layer, a light absorbing layer, and a wavelength filter layer of the first conductive type located in a predetermined region above the wavelength filter layer of the second conductive type; Protective films positioned on the semiconductor laser and the photodetector, respectively; And a light absorption window made to expose a portion of the surface of the wavelength filter layer of the first conductive type.

In addition, the method for fabricating a wavelength division bidirectional optical communication device according to the present invention includes a first step of preparing a semiconductor substrate of a first conductivity type; A second step of sequentially forming a first conductive buffer layer, an active layer, and a second conductive buffer layer on the semiconductor substrate, and forming an etching mask pattern defining a semiconductor laser region; A third step of wet etching the second conductive buffer layer, the active layer, and the first conductive buffer layer by an etching process using the etching mask pattern; A fourth step of forming a current blocking layer insulating the semiconductor laser region on the resultant of which the third step is completed, but not forming the upper portion of the etch mask pattern; A fifth step of sequentially forming a second conductive wavelength filter layer, an etch stop layer, a light absorption layer, and a first conductive type wavelength filter layer on the resultant of the fourth step; And a sixth step of performing a selective etching process to form a photodetector including a wavelength filter layer, a light absorption layer, and an etch stop layer of the first conductivity type overlapping the semiconductor laser.

The wavelength division multiplexing device in which the semiconductor laser and the photodetector of the present invention are integrated into a single chip (hereinafter referred to as a device chip) first forms a semiconductor laser structure that emits light of a short wavelength on an N-type semiconductor substrate, and then It has a vertically integrated structure that forms a photodetector structure that absorbs light of a long wavelength, and the stacked semiconductor laser and the photodetector share a P-type semiconductor layer with each other, thereby forming a vertically formed NPN structure. The P-type semiconductor layer of the NPN structure and the N-type semiconductor layer positioned on the photodetector absorb the short wavelength transmission light emitted from the semiconductor laser and pass the long wavelength reception light absorbed by the photodetector. It is composed of a material having an energy band gap to act as a wavelength filter. Therefore, when the device chip of this structure is optically coupled with one strand of optical fiber, the light of short wavelength from the semiconductor laser of the device chip is coupled to the optical fiber and transmitted, and the light of long wavelength from the optical fiber is coupled to the photodetector of the device chip. Is received. At this time, the light emitted from the semiconductor laser is reflected by the optical fiber cross-section and directed toward the photodetector, so the light is filtered by the common P-type semiconductor layer and the N-type semiconductor layer of the photodetector, and thus is not absorbed by the absorption layer of the photodetector and is not converted into photocurrent. .

Hereinafter, the wavelength division multiplexing device in which the semiconductor laser and the photodetector are integrated into a single chip include a planar buried heterojunction structure semiconductor laser (PBH-LD) and a 1.55 wavelength of 1.3 μm. A case in which InGaAs PIN-PD (PIN Photodiode, hereinafter referred to as a photodetector) having a 탆 wavelength is integrated will be described in detail with reference to the accompanying drawings.

1 is a plan view of a wavelength division multiplexing device in which a semiconductor laser and a photodetector are integrated into a single chip, and FIG. 2 is a wavelength division multiplexing device in which a semiconductor laser and a photodetector are integrated into a single chip according to the present invention. The structure of a wavelength division multiplexing element is demonstrated with reference to this as sectional drawing of BB '.

First, as shown in FIG. 2, an N-type InP buffer layer 8, an undoped InGaAsP active layer (hereinafter referred to as an active layer) 9, a P-type InP buffer layer 17, and the like on the N-type InP substrate 7 P-type InP cladding layer (hereinafter referred to as cladding layer) 10, P-type InGaAsP resistive contact layer 11, P-type InGaAsP resistive contact layer 11, undoped InP etch stop The layer 12, the undoped InGaAs light absorbing layer (hereinafter referred to as the light absorbing layer) 13, and the N-type InGaAsP resistive contact layer 14 have a structure in which the photodetectors 2 are sequentially stacked.

Here, the semiconductor laser 1 and the photodetector 2 share a P-type InGaAsP resistive contact layer 11 with each other, and an N-type InGaAsP resistive contact layer 14, a P-type InGaAsP resistive contact layer 11, and an N-type substrate. It is provided with (7) to form a vertically formed NPN structure. In such a vertically integrated structure, the active layer 9 of the semiconductor laser 1 and the light absorbing layer 13 of the photodetector 2 are located very close to each other within 2 µm to 3 µm so that the same optical fiber (" Optical coupling to " 25 " is facilitated for both of these devices to improve optical transmission and reception characteristics.

Further, an N-type InGaAsP resistive contact layer 14 positioned at the upper and lower portions of the photodetector 2, and a P-type InGaAsP resistive contact making ohmic contact with the N-type electrode 4 and the P-type common electrode 3 of the photodetector. The layer 11 is composed of a material having an energy band gap which absorbs light 15 of the wavelength of transmission from the semiconductor laser and passes light 16 of the wavelength of reception, which enters the photodetector, thereby acting as a selective filter of the wavelength. This minimizes the interference between the transmission and reception signals.

Next, the wavelength division multiplexing device according to the present invention will be described in detail with respect to the process steps with reference to FIGS. 3A to 3G.

As shown in FIG. 3A, an N-type InP buffer layer 8 and an active layer having a wavelength of 1.3 mu m are formed by an epitaxial crystal growth method such as MOCVD (Metal-Organic Chemical Vapor Deposition) on the N-type InP substrate 7. ), And the P-type InP buffer layer 17 is sequentially grown. In this case, the active layer 9 may be formed in a multilayer structure such as a simple InGaAsP single layer or a multi quantum well (MQW) structure.

As shown in FIG. 3B, a nitride film 18 is formed on the P-type InP buffer layer 17 as an etching mask layer for defining a region of the semiconductor laser 1, and an etching process is performed. As the layer, a dielectric insulating film such as nitride film 18 may be used, and the etching depth is etched to the N-type InP buffer layer 8 or the N-type InP substrate 7.

As shown in FIG. 3C, an epitaxial crystal growth method such as MOCVD is performed while leaving the nitride film 18 used as an etching mask after the above-described etching process. The epitaxial layer grown here is a P-type InP layer 19, an N-type InP layer 20, and a P-type InP layer 21 so that crystal growth may be performed only in a region where the nitride film 18 is not present. 1) It acts as a current blocking layer that induces current to flow through only the region.

As shown in FIG. 3D, after removing the nitride film 18 used as the etching mask, the P-type cladding layer 10, P-type InGaAsP resistive contact layer 11 having a wavelength between 1.3 mu m and 1.55 mu m is disposed thereon. , An undoped InP etch stop layer 12, a light absorbing layer 13, and an N-type InGaAsP resistive contact layer 14 having the same wavelength as the P-type InGaAsP resistive contact layer 11 are sequentially formed. Here, the P-type cladding layer 10 becomes a P-side cladding layer of the semiconductor laser 1, and the P-type InGaAsP resistive contact layer 11 emits light having a wavelength of 1.3 μm emitted from the semiconductor laser 1. Absorption of (15) serves as a wavelength filter that prevents a portion of the light 15 having a wavelength of 1.3 mu m from entering the light absorbing layer 13 of the photodetector even when reflected from a cross section of the optical fiber, and undoped InP etching stop. The layer 12 serves as an etch stop layer for selective etching when defining the photodetector 2 region by a subsequent etching process. The light absorbing layer 13 becomes a light absorbing layer of the photodetector 2 with respect to light 16 having a wavelength of 1.55 µm emitted from the optical fiber, and the N-type InGaAsP resistive contact layer 14 emits from the semiconductor laser 1. A portion of the light 15 having a wavelength of 1.3 μm is prevented from entering the light absorbing layer 13 of the photodetector even if it is reflected from the end face of the optical fiber, that is, the transmitting semiconductor laser light 15 absorbs the number of the wavelength of 1.55 μm. The credit light 16 acts as a wavelength filter for passing.

As shown in FIG. 3E, a wet etching method selectively etches an N-type InGaAsP resistive contact layer 14, a light absorbing layer 13, and an undoped InP etch stop layer 12 to define a photodetector 2 region. The etchant is used to etch the N-type InGaAsP resistive contact layer 14, the light absorbing layer 13, and the undoped InP etch stop layer 12 in the remaining portions except for the photodetector region.

As shown in FIG. 3F, a nitride film 5 is formed on the entire structure by a deposition method such as PECVD (Plasma Enhanced Chemical Vapor Deposition), and then subjected to selective etching to perform an N-type InGaAsP resistive contact layer 14 and The P-type InGaAsP resistive contact layer 11 is exposed.

Here, the exposure of the N-type InGaAsP resistive contact layer 14 is for forming a light absorption window portion of the photodetector 2, and the exposure of the P-type InGaAsP resistive contact layer 11 is an N-type InGaAsP resistive contact layer 14. ) And P-type InGaAsP resistive contact layer 11 to form a resistive contact window.

As shown in Fig. 3G, the N-type electrode 4 of the photodetector, the P-type common electrode 3 of the photodetector 2 and the semiconductor laser 1 are formed, respectively, and the N-type InGaAsP resistive contact layer 14, respectively. ) And metal contacted with the P-type InGaAsP resistive contact layer 11 are formed by a lift-off method and heat-treated using a Rapid Thermal Annealing (RTA) device. Then, the back surface of the wafer is polished to a predetermined thickness, and metals in ohmic contact with the N-type InP substrate 7 are deposited to form the N-type electrode 6 of the semiconductor laser, and then heat-treated using an RTA apparatus.

The wavelength division multiplexing element in which the process according to the above-described process sequence is completed may be formed by cleaving the resonator of the semiconductor laser 1 and separating it into chips.

Next, referring to FIG. 4, the principle of optically coupling an element chip in which the semiconductor laser 1 and the photodetector 2 are integrated with an optical fiber is based on a V-grooveed silicon substrate 22. The case where the element chip and the optical fiber 25 are fixed and optically coupled is described.

The device chip is flipped so that the photodetector 2 of the above-described device chip faces toward the V-groove 23 where the optical fiber 25 is to be located and flip chip bonding at a predetermined position of the silicon substrate 22. The optical fiber 25 is fixed in the V-groove 23. The position of the flip chip bonding pad on the silicon substrate 22 and the width of the V-groove 23 are determined according to the degree of alignment of the semiconductor laser active layer 9 and the core 26 of the optical fiber. The position of the flip chip bonding pad and the width of the V-groove 23 should be designed so that the semiconductor laser active layer 9 and the core 26 of the optical fiber are aligned in a line.

After the flip chip bonding is finished, the semiconductor laser 1 is oscillated by applying a current to the P-type common electrode 3 and the N-type electrode 6 of the semiconductor laser. Light 15 is emitted and light 1.3 having a wavelength of 1.3 탆 is optically coupled to the fiber core 26 and transmitted through the optical fiber. On the other hand, the light 16 having a wavelength of 1.55 μm transmitted from the optical fiber 25 is emitted from the optical fiber core 26 toward the device chip, and the light component which is directed downward from the light 16 having the wavelength of 1.55 μm is emitted. It is absorbed into the absorption layer 13 of the photodetector through the device chip cross section or the photodetector absorption window and converted into current. This current component is detected by an external circuit through the P-side common electrode 3 subjected to the reverse bias voltage and the N-type electrode 4 of the photodetector.

At this time, in order for the light 16 incident on the photodetector to be effectively focused on the light absorption window, the metal reflective film 24 is coated on the inclined surface of the silicon substrate V-groove 23 so that the light directed toward the bottom of the chip is seen in FIG. As described above, the metal film 24 is absorbed toward the photodetector after reflection to improve the reception sensitivity of the photodetector.

Also, among the light 15 having a wavelength of 1.3 탆 emitted from the semiconductor laser 1, the light component returned to the device chip by reflecting light at the cross section of the optical fiber 25 is a region of the photodetector 2 which is a structural feature of the present invention. It is absorbed by the N-type InGaAsP resistive contact layer 14 and the P-type InGaAsP resistive contact layer 11 serving as a filter for light having a wavelength of 1.3 μm located above and below the transmission optical signal for the received optical signal 16. The interference of (15) can be minimized.

As described above, the optical device according to the present invention is a wavelength division bidirectional optical communication module for simultaneously transmitting a short wavelength transmission and a long wavelength reception optical signal using a single optical fiber, wherein the wavelength division in the form of a separate optical waveguide is performed. Without the multiplexing device, the semiconductor laser for transmitting light and the photodetecting device for photoreceiving are vertically integrated on the same semiconductor substrate, so that the active area of the semiconductor laser and the light absorbing area of the photodetector element are located very close together and at the top and bottom of the photodetector. By combining a material with an energy band gap that absorbs the shorter wavelengths of light coming in and enters the photodetectors, the optical coupling with the same optical fiber is facilitated for both of these devices. Also minimizes interference between received signals Can achieve effects such as miniaturization, cost reduction and improved production characteristics of the wavelength division two-way optical communication optical module according to the number of parts reduced, and optical packaging process simplified.

Claims (15)

A first conductive semiconductor substrate; A semiconductor laser including a first conductive buffer layer, an active layer, a second conductive buffer layer, and a second conductive wavelength filter layer positioned on the semiconductor substrate; A photodetector comprising an etch stop layer, a light absorbing layer, and a wavelength filter layer of the first conductive type located in a predetermined region above the wavelength filter layer of the second conductive type; Protective films positioned on the semiconductor laser and the photodetector, respectively; And A light absorption window is formed to expose a portion of the surface of the first conductive type wavelength filter layer. Wavelength division bidirectional optical communication device comprising a. The method of claim 1, The wavelength division bidirectional optical communication device, A first electrode of the photodetector contacting the first conductive wavelength filter layer through the light absorption window; A second electrode of the photodetector and a first electrode of the semiconductor laser contacted to the wavelength filter of the second conductive type through a contact window formed by an etching process of a protective film positioned on the wavelength filter of the second conductive type; Common electrode used as; And A second electrode of the semiconductor laser positioned under the semiconductor substrate Wavelength division bidirectional optical communication device further comprising. The method of claim 2, And a second electrode of the photodetector is formed on the exposed wavelength filter layer of the first conductive type so that two electrodes of the photodetector and the semiconductor laser are formed, respectively. The method of claim 1, The active layer of the semiconductor laser device for wavelength division bidirectional optical communication that emits light of the first wavelength. The method of claim 1, And a light absorbing layer of the photodetector absorbs light of a second wavelength having a wavelength larger than that of the first wavelength. The method of claim 1, The wavelength filter layer of the first and second conductive type is a wavelength division bidirectional optical communication device to absorb the light of the first wavelength. The method of claim 1, And the semiconductor substrate, the first and second conductive buffer layers, and the etch stop layer are formed using an InP film. The method of claim 1, The active layer, the wavelength filter layer of the first and second conductive type is made of InGaAsP film, and the light absorption layer is made of InGaAs film for wavelength division bidirectional optical communication device. The method of claim 6, The wavelength filter layer of the first and second conductive type is a wavelength division bidirectional optical communication device for passing the light of the second wavelength. A first step of preparing a first conductive semiconductor substrate; A second step of sequentially forming a first conductive buffer layer, an active layer, and a second conductive buffer layer on the semiconductor substrate, and forming an etching mask pattern defining a semiconductor laser region; A third step of wet etching the second conductive buffer layer, the active layer, and the first conductive buffer layer by an etching process using the etching mask pattern; A fourth step of forming a current blocking layer insulating the semiconductor laser region on the resultant of which the third step is completed, but not forming the upper portion of the etch mask pattern; A fifth step of sequentially forming a second conductive wavelength filter layer, an etch stop layer, a light absorption layer, and a first conductive type wavelength filter layer on the resultant of the fourth step; And A sixth step of forming a photodetector comprising a wavelength filter layer, a light absorption layer, and an etch stop layer of a first conductivity type overlapping the semiconductor laser by performing a selective etching process; A method of manufacturing a wavelength division bidirectional optical communication device comprising a. The method of claim 10, After the sixth step A seventh step of forming a protective film on the resultant of the sixth step is completed; An eighth step of exposing the second conductive wavelength filter layer by selective etching of the passivation layer to form a light absorption window and exposing the first conductive wavelength filter layer; A ninth step of forming the photodetector first electrode in contact with the first conductive wavelength filter layer through the light absorption window; A second electrode of the photodetector and a first electrode of the semiconductor laser contacted to the wavelength filter of the second conductive type through a contact window formed by an etching process of a protective film positioned on the wavelength filter of the second conductive type; Forming a tenth step; And An eleventh step of forming a second electrode of the semiconductor laser under the semiconductor substrate A method of manufacturing a wavelength division bidirectional optical communication device comprising a. The method of claim 10, The active layer of the semiconductor laser is a method of manufacturing a device for wavelength division bidirectional optical communication that emits light of a first wavelength. The method of claim 10, And a light absorption layer of the photodetector absorbs light of a second wavelength having a wavelength larger than that of the first wavelength. The method of claim 10, And the wavelength filter layers of the first and second conductive types absorb the light of the first wavelength. The method of claim 10, And the wavelength filter layers of the first and second conductive types allow the light of the second wavelength to pass through.

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