JPH08125267A - Optical semiconductor element and manufacture thereof - Google Patents

Abstract

PURPOSE: To hardly exert etching damage or the like on an optical semiconductor element when both parts of the element formed by integrating a semiconductor laser part and a light modulator part are optically coupled with each other and an electrical separation part for separating electrically the laser and modulator parts from each other is formed by etching. CONSTITUTION: The width of a scheduled formation part of an electrical separation part 39 of a striped semiconductor laser (a mesa structure 33), which is provided in common to a semiconductor laser part 25, a light modulator part 37 and the electrical separation part 39, is made narrow by a wet etching. Provided that parts retreated by a prescribed distance, which is set in consideration of etching damage or the like, is etched from the respective end parts which are located on the sides of the part 39.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical semiconductor element which can be used as a light source for optical communication and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a conventional example of this kind of optical semiconductor device, for example, a document (IEICE Transactions CI, Vol.J77-CI, N
o.5, pp. 268-275 (1994.5)). It is an optical semiconductor device in which a semiconductor laser section and an optical modulator section are monolithically integrated. In this type of device, it is necessary to electrically separate the semiconductor laser section and the optical modulator section while ensuring optical coupling between them. Therefore, in the optical semiconductor element disclosed in this document, stripe-shaped In
While each part of the GaAsP-based MQW layer is used as part of each of the constituent elements of the semiconductor laser section and the optical modulator section, both parts of the MQW layer are optically used by utilizing the MQW layer part between both parts. It was coupled and electrically isolated. Specifically, the semiconductor laser unit and the optical modulator unit have separate electrodes, and M is the distance between the semiconductor laser unit and the optical modulator unit.
The contact layer is removed on the QW layer portion (electrical isolation portion), and this electrical isolation portion has its width reduced to some extent and its length increased to some extent in order to increase electric resistance. It was Specifically, in the above document, the widths of the stripe-shaped semiconductor layers (such as the MQW layer and the upper clad layer) in the electrical separation section and the optical modulator section are both set to about 2.5 to 3 μm. This semiconductor layer is processed by active etching. Further, the length of the electrical isolation portion is set to about 50 μm.

[0003]

However, in the conventional optical semiconductor device, since the width of both the electrical isolation portion and the optical modulator portion is the same, if the width is narrowed in order to increase the electrical resistance of the electrical isolation portion, the light It may deteriorate the characteristics of the modulator.

Further, when forming an optical modulator portion and an electrical separation portion in a conventional optical semiconductor element, if the optical modulator portion and the electrical isolation portion are formed by the RIE method, there is a risk that etching damage may affect the optical modulator portion and the like, so the device life is reduced. There is a risk of deterioration. Further, when the optical modulator section and the separation section are formed by the wet etching method, there is a risk of etching the modulator section and the semiconductor laser section due to poor controllability.

[0005]

Therefore, according to the first invention of this application, a semiconductor laser portion including a part of a stripe-shaped semiconductor layer as an element constituent element and another part of the stripe-shaped semiconductor layer are provided. An optical modulator portion included as an element constituent element, and a portion of the stripe-shaped semiconductor layer between the semiconductor laser portion and the optical modulator portion optically couples the two but electrically separates them. In the optical semiconductor element serving as the electrical isolation portion, the width of the stripe-shaped semiconductor layer in the electrical isolation portion is set to a predetermined width narrower than other portions.

According to the second invention of this application, a semiconductor laser section including a part of a stripe-shaped semiconductor layer as an element constituent element, and an optical modulation including another part of the stripe-shaped semiconductor layer as an element constituent element. And a portion between the semiconductor laser portion and the optical modulator portion of the stripe-shaped semiconductor layer is an electrical separating portion that optically couples the two and electrically separates them. In forming an optical semiconductor element in which the width of the stripe-shaped semiconductor layer in the electrical isolation portion is a predetermined width narrower than other portions, formation of the electrical isolation portion is performed. Is performed by etching a portion of the striped semiconductor layer where the electrical isolation portion is to be formed to have the predetermined width. Moreover, this etching is performed at a distance from the end of each of the semiconductor laser section and the optical modulator section on the side of the electrical isolation section in consideration of etching damage and / or etching accuracy for the semiconductor laser section and the optical modulator section. It is characterized in that it is performed only for the part that has been evacuated.

In the first and second inventions, the predetermined width of the electrical isolation portion is determined according to the design of the optical semiconductor element, and is, for example, the optical distance between the semiconductor laser portion and the optical modulator portion. The width can be determined in consideration of a width suitable for both stable coupling and electrical separation.

Further, in the second invention, the specific value of the distance considering both or one of the etching damage and the etching accuracy is also determined according to the design of the optical semiconductor element. For example, the etching method, its condition, the element It can be a value that takes into consideration the dimensions. Further, in the second invention, the end on the side of the electrical isolation portion in the semiconductor laser section means, for example, the end of the active layer of the semiconductor laser, and the end on the side of the electrical isolation portion in the optical modulator section. The term, for example, means a portion corresponding to an end of an electrode for a light modulator.

[0009]

According to the first invention of this application, the width of the electrical isolation portion can be adjusted independently.

According to the second invention of this application, each of the semiconductor laser section and the optical modulator section is etched due to poor etching controllability, and each of the semiconductor laser section and the optical modulator section is etched. The electrical isolation portion can be formed while avoiding damage.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the first and second inventions of this application will be described below with reference to the drawings. It should be noted that the drawings used for the description schematically show the dimensions, shapes, and positional relationships of the respective constituents to the extent that these inventions can be understood. Further, in each of the drawings used for description, the same components are denoted by the same reference numerals.

First, in this embodiment, the n-type InP substrate 1 is used as a base on which the semiconductor laser section and the optical modulator section are integrated.
Prepare 1. On this n-type InP substrate 11, an InGaAsP-based semiconductor layer 13 having a multiple quantum well (MQW) structure in this embodiment is used as a semiconductor layer used as an element constituent element in each of the semiconductor laser section and the optical modulator section. Are epitaxially grown. Furthermore, this M
On the InGaAsP-based semiconductor layer 13 having the QW structure,
An InP layer 15 (details will be described later) for etching stop is grown, and then a semiconductor layer for forming a waveguide layer (for example, InGaAsP layer) is formed on the InP layer 15 as a semiconductor layer for forming a semiconductor laser portion. 17, an active layer forming semiconductor layer (here, an InGaAsP-based semiconductor layer having an MQW structure) 19 and a diffraction grating forming semiconductor layer (for example, a p-type InGaAs layer) 21 are grown in this order (FIG. 1).
(A), FIG. 1 (B)). Note that FIG. 1A is a cross-sectional view of the sample in which the formation up to the semiconductor layer 21 is completed, and FIG. 1B is a plan view of the sample as seen from the semiconductor layer 21 side. The cross section taken along the line I-I of FIG. 1B corresponds to FIG.

The semiconductor laser section may not have the MQW structure or may have no diffraction grating. In that case, the configurations of the semiconductor layers 17 and 19 are changed accordingly.

Next, as shown in the sectional view of FIG. 2, a diffraction grating 21a is formed on the p-type InGaAsP layer 21 by a known method. This is to obtain a distributed feedback semiconductor laser. Specifically, the surface of the p-type InGaAsP layer 21 is processed into a waveform having a predetermined pitch to obtain this diffraction grating 21a. Next, the p-type InGaAsP layer 21, the active layer forming semiconductor layer 19, and the waveguide layer forming semiconductor layer, which are present on the regions where the optical modulator portion and the electrical isolation portion of the InGaAsP-based semiconductor layer 13 are to be formed, are formed. Each part of 17 is selectively removed. This removal can be performed using, for example, hydrofluoric acid, which is a selective etching solution for InGaAaP. During this etching, the InGaAsP-based semiconductor layer 13 is protected by the InP etching stop layer 15 thereabove. After that, the p-InP clad layer 2 is formed on the entire surface of this sample.
Grow 3

Next, as shown in the top view of FIG. 3, the p-type InGaAsP layer 21, the active layer forming semiconductor layer 19, and the waveguide layer forming semiconductor layer 17 are left in order to define the semiconductor laser portion 25. The portion is processed by a known fine processing technique so that the width W ₁ becomes a mesa structure 25a having a width of about 1.5 μm. In addition, the InP etching stop layer 15 and In
The GaAsP-based semiconductor layer 13 is processed by a known fine processing technique so as to have a stripe-shaped mesa structure 27 having a width W ₂ of about 20 μm. Next, since both sides of the mesa structure 25a of the semiconductor laser section 25 are filled with the current blocking layer, the p-type InP current blocking layer and the n-type InP current blocking layer are formed on the sample on which the mesa structure 25a and the mesa structure 27 have been formed. Grow in this order (not shown in FIG. 3).

Next, a p-type InP clad layer 29 and a contact layer 31 are grown in this order on this sample, as shown in the sectional view of FIG. Next, in order to reduce the electrostatic capacitance in the optical semiconductor element, the contact layer 31, the p-type InP clad layer 29, the current block layer, I
The nP etching stop layer 15 and the InGaAsP-based semiconductor layer 13 are formed into a well-known fine structure 33 having a width W ₃ (see FIG. 3) of about 10 μm and having the mesa structure 25 a and the mesa structure 27 at the center. Process with processing technology. In this example, the mesa structure 33 is obtained by forming grooves reaching the substrate 11 on both sides of the portion of the sample where the mesa structure is to be formed. In this embodiment, the mesa structure 33 corresponds to the stripe-shaped semiconductor layer in the present invention. FIG. 4B is a diagram showing a sample on which the mesa structure 33 has been formed, just as a cross section taken along line III-III in FIG. In FIG. 4 (B), 3
3a is a groove formed to obtain the mesa structure 33, and 35
Symbols a and 35b are remnants of n and p InP layers formed to form the p-type current blocking layer and the n-type current blocking layer of the semiconductor laser section 25 (see FIG. 3).

Next, as shown in the top view of FIG. 5, the semiconductor laser section 25 and the optical modulator section 37 are optically coupled to each other but electrically separated from each other in this mesa structure 33. The electrically isolated portion 39 is formed (see FIG. 5).
Therefore, specifically, the contact layer 31 in the portion of the mesa structure 33 where the electrical isolation portion 39 is to be formed is removed, and
The portion of the mesa structure 33 corresponding to the region where the electrical isolation portion 39 is to be formed is etched so that the width thereof becomes a predetermined width W ₄ narrower than other portions. In this case, this etching was performed with a bromine-based etchant. However, this etching is performed by the semiconductor laser portion 25 in the mesa structure 33.
And the electrical separating section 3 of the portion that constitutes the optical modulator section 37.
It is performed on a portion retracted from the end portion on the 9 side by distances t ₁ and t ₂ (see FIG. 5) in consideration of etching damage and / or etching accuracy with respect to the semiconductor laser portion 25 and the optical modulator portion 37. This has the advantage that the etching does not reach the semiconductor laser portion 25 and the optical modulator portion 37 even if an etching method having a problem of controllability such as wet etching is used. In addition, since wet etching can be positively used, the damage of the crystal due to etching is RI.
The advantage is that it is less than when using dry etching such as E. Further, even when dry etching is used, there is an advantage that the influence of etching damage on the semiconductor laser section and the optical modulator section is reduced.

Note that these t ₁ and t ₂ are determined according to the design. Of course, there may be a case where t ₁ = t ₂ .
In the case of this embodiment, t ₁ is a predetermined distance of 5 μm or more from the end of the electrode for the optical modulator section 37 (the one provided on the contact layer of the optical modulator section (not shown)), and t ₂ is a predetermined distance of 5 μm or more from the end of the mesa structure 25 a of the semiconductor laser section 25. In addition, in this embodiment, the width W ₄ of the electrical separating portion 39 is about 3 μm and the length X (see FIG. 5) is about 50 μm. The unnecessary portion of the mesa structure 33 is etched so as to have a substantially rectangular shape. Next, one electrode is formed on the back surface of the substrate 11 and the other electrode is formed on each of the semiconductor laser section 25 and the optical modulator section 37 by a known method. Then, the optical semiconductor element 41 (see FIG. 5) of the embodiment is divided from the wafer by a suitable method such as cleavage. In this embodiment, each of the semiconductor laser section 25 and the optical modulator section 37 of the optical semiconductor element 41 has a length of about 250 μm.

In order to deepen the understanding of the present invention, the operation of the optical semiconductor element 41 of the embodiment will be briefly described.

Laser oscillation occurs here when a forward current is applied to the semiconductor laser section 25. Further, by applying a reverse bias voltage to the optical modulator section 37, the optical absorption coefficient here changes. The light emitted from the semiconductor laser portion 25 is coupled to the InGaAsP-based semiconductor layer 13 having the MQW structure, and further reaches the optical modulator portion 37 through a portion corresponding to the electrical separating portion 39 of the semiconductor layer 13. Here, the light absorption coefficient is modulated by modulating the voltage application of the optical modulator section 37, and as a result, the laser light which passes through the optical modulator section and emerges is in a modulated form. The electrical isolation portion 39 has a high electrical resistance because it has a narrow width and no contact layer is provided thereon. Suppression of electric signal leakage between the modulator units.

Although the embodiments of the first and second inventions of the present application have been described above, the inventions are not limited to the above-mentioned embodiments.

For example, the planar shape of the electrical isolation portion 39 is not limited to the rectangular shape, but may be any shape according to the design. For example, as shown in FIG. 6, the electrical separating portion 39 has a predetermined width because the width becomes narrower from the semiconductor laser portion 25 side and the optical modulator portion 37 side toward the center of the electrical separating portion 39. W ₄ and may be a shape such that. When the portion of the mesa structure 33 where the electrical separation portion 39 is to be formed is formed by the wet etching method, it is considered that etching traces often become as shown in FIG. 6 due to the characteristics of the crystal. This is an advantage when discussing the long-term device life because the crystal plane is exposed.

The material and conductivity type of the optical semiconductor element are not limited to the above examples. The present invention can be applied to an optical semiconductor element made of another material and an optical semiconductor element having a conductivity type opposite to that of the embodiment.

[0024]

As is apparent from the above description, according to the first invention of this application, the width of the electrical isolation portion can be adjusted independently, so that the electrical isolation portion can be easily optimized.

Further, according to the second invention of this application, the etching of the semiconductor layer at the time of forming the electrical isolation portion is performed in a state of being retracted from the respective end portions of the semiconductor laser portion and the optical modulator portion by a predetermined distance. Therefore, each of the semiconductor laser section and the optical modulator section is etched due to poor etching controllability, and each of the semiconductor laser section and the optical modulator section is prevented from being damaged by etching, and the electrical isolation section is prevented. Can be formed. Therefore, it is possible to suppress deterioration of element characteristics due to poor etching controllability during formation of the electrical isolation portion and etching damage, as compared with the related art.

[Brief description of drawings]

FIG. 1A and FIG. 1B are diagrams for explaining an example.

FIG. 2 is a view following FIG. 1 for explaining the embodiment.

FIG. 3 is a view following FIG. 2 for explaining the embodiment.

4A and 4B are views following FIG. 3 for explaining the embodiment.

FIG. 5 is a view following FIG. 4 for explaining the embodiment.

FIG. 6 is a diagram for explaining another embodiment.

[Explanation of symbols]

11: Base (n-type InP substrate) 13: Semiconductor laser section and optical modulator section that are element components (InGaAs semiconductor layer of MQW structure) 15: Etching stop layer (InP layer) 17: Waveguide Layer forming semiconductor layer (InGaAsP layer) 19: Active layer forming semiconductor layer 21: Diffraction grating forming semiconductor layer 21a: Diffraction grating 23: Cladding element 25: Semiconductor laser section 25a: Mesa structure 27: Mesa structure 33: Mesa structure (Striped Semiconductor Layer According to the Present Invention) 33a: Groove 37: Optical Modulator Section 39: Electrical Separation Section 41: Optical Semiconductor Element of Example

Claims (2)

[Claims] 1. A semiconductor laser section including a part of a stripe-shaped semiconductor layer as an element constituent element, and an optical modulator section including another part of the stripe-shaped semiconductor layer as an element constituent element, the stripe shape In the optical semiconductor element, a portion of the semiconductor layer between the semiconductor laser portion and the optical modulator portion is an electrical separating portion that optically couples the two, but electrically separates them. An optical semiconductor element, wherein the width of the semiconductor layer of the semiconductor layer in the electrical isolation portion is a predetermined width narrower than other portions. 2. A semiconductor laser section including a part of a stripe-shaped semiconductor layer as an element constituent element, and an optical modulator section including another part of the stripe-shaped semiconductor layer as an element constituent element, the stripe shape In the semiconductor layer, a portion between the semiconductor laser portion and the optical modulator portion is an optical semiconductor element which is an electrical separating portion that optically couples the two, but electrically separates them. In manufacturing an optical semiconductor element in which the width of the stripe-shaped semiconductor layer in the electrical isolation portion is a predetermined width narrower than other portions, formation of the electrical isolation portion is performed by forming the electrical isolation portion of the stripe-shaped semiconductor layer. The portion where the electrical separation portion is to be formed is etched to have the predetermined width, and the etching is performed by the semiconductor laser portion and the optical modulator portion. Method for manufacturing an optical semiconductor device and performing the end side with respect to the semiconductor laser portion and both the etching damage and etching accuracy of the optical modulator unit or only the saved partial distance in consideration of one.