JPH04199680A - Optical semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable light to travel effectively by a method wherein a first and a second waveguide layer larger than a substrate in refractive index and an upper layer whose refractive index is smaller than that of the substrate are provided, and the thickness ratio of the first waveguide layer to the second waveguide layer is specified. CONSTITUTION:A guide layer 11 formed of GaInAsP 3.2 in refractive index, 0.15mum in thickness, and 1.1mum in PL emission wavelength, a stop layer 12 formed of InP 200Angstrom in thickness, an active layer 14 formed of GaInAsP 3.5 in refractive index, 0.15mum in thickness (T1), and 1.55mum in PL emission wavelength, and an absorbing layer 15 formed of GaInAsP 3.43 in refractive index and 1.43mum in PL emission wavelength adjacent to the active layer 14 are formed on an InP substrate 10. Furthermore, the layers 14 and 15 are covered with an upper layer 16 of InP 3.098 in refractive index. At this point, the thickness t1 of the active layer 14 to the thickness t2 of the absorbing layer or the thickness ratio t2/t1 is 1:1/3-3. By this setup, light can be lessened in reflection at a joint between the waveguide layers of optical semiconductor elements, and in result light can be effectively transmitted.

Description

[Detailed Description of the Invention] [Table of Contents] ・Overview, Field of Industrial Use, Conventional Technology (Figure 4) ・Problem to be solved by the invention, Means and operation for solving the problem (Figure 3)・Example (FIGS. 1 and 2) ・Effects of the invention [Summary] Regarding an optical semiconductor device and its manufacturing method, more specifically, an optical semiconductor device in which a plurality of optical semiconductor elements are integrated on the same substrate and its manufacturing method. Regarding the manufacturing method, the purpose is to provide an optical semiconductor device and its manufacturing method that can reduce the reflection of light at the junction between the waveguide layers of each optical semiconductor element and efficiently propagate light. The device includes first and second waveguide layers disposed on a substrate with their ends adjacent to each other and having a refractive index greater than a refractive index of the substrate; and the first and second waveguide layers. and an upper layer having a refractive index smaller than the refractive index of the first and second waveguide layers; The film thickness ratio t 2 /l of the film thickness t2 of the waveguide layer is 1/3 or more and 3 or less.

(Industrial Application Field) The present invention relates to an optical semiconductor device and a method for manufacturing the same, and more specifically, to an optical semiconductor device in which a plurality of optical semiconductor elements are integrated on the same substrate and a method for manufacturing the same.

In recent years, there has been a demand for optical semiconductor devices that include not only a single optical semiconductor element but also a plurality of optical semiconductor elements integrated on the same substrate.

In such optical semiconductor devices, it is necessary to transmit light between elements that have different functions, but in such cases, it is necessary to reduce the reflection of light at the junction between the waveguide layers that transmit light as much as possible. is important.

[Prior Art] FIGS. 4(a) to 4(e) are diagrams illustrating a method of manufacturing a conventional optical semiconductor integrated circuit device.

First, as shown in the same figure (a), a substrate 1 made of InP
Above are a guide layer 2 made of Ga1nAsP, a stop layer 3 made of InP, an active layer 4 made of Ga1nAsP, and InP.
The first upper layer 5 consisting of
E) formed by a method.

Next, as shown in FIG. 4B, the first upper layer 5 and the active layer 4 are selectively etched using a resist pattern (not shown) as a mask until the etching stops at the underlying stop layer 3.

Next, as shown in FIG. 4C, on the exposed stop layer 3 and adjacent to the first upper layer 5a and the active layer 4a, a layer of the same material as the active layer 4a but with a different composition is formed. Ga1nAs
The absorption layer 6 and the second upper layer 7 made of P are formed by selective growth using the LPE method. At this time, due to the nature of selective growth, the absorption layer 6 formed is usually thickest along the side wall surfaces of the adjacent first upper layer 5a and active layer 4a, and gradually increases in thickness as it moves away from the side wall surfaces. When the film thickness decreases beyond a certain distance, the cross-sectional shape becomes such that the film thickness becomes approximately constant.

Next, the first upper layer 5a, the active layer 4a, the adjacent absorption layer 6, and the second upper layer 7 are patterned to have a width of approximately 1.5 cm.
A subsequent waveguide layer is formed consisting of an active layer 4b, an absorption layer 6a and a second upper layer 7a. Next, the same figure (d
), the remaining first upper layer 5b, active layer 4b, absorption layer 6a, and second upper layer 7a are covered with a high-resistance buried layer made of InP by selective growth using the LPE method. A mixed layer 7b is formed. Note that the first and second upper layers 5b and 7a constitute one upper layer 8.

Thereafter, when electrodes are formed on the surface of the second upper layer 7a on the active layer 4b and on the surface of the second upper layer 7a on the absorption layer 6a, a light generation part including the active layer 4b and a light modulation part including the absorption layer 6a are formed. A section is formed. Note that (e) in the same figure is a top view of (d) in the same figure.

In such an optical semiconductor integrated circuit device, the light generated in the active layer 4b of the light generation section is transmitted to the light modulation section, and
A signal is loaded by changing the intensity of light passing through the absorption layer 6a by applying a voltage to the light modulation section.

[Problem to be solved by the invention]

However, in the optical semiconductor device created in this way, the intensity of light that enters the absorption layer 6a from the active layer 4b, is transmitted through the absorption layer 6a, and comes out may be extremely reduced.
This has become a problem.

The reason for this is: (1) As shown in FIG. 4(d), the adjacent first upper layer 5
Since the absorbing layer 6a is formed thickly on the side wall surfaces of the active layer 4b and the active layer 4b, the upper part of the absorbing layer 6a comes into contact with the first upper layer 5b having a different refractive index from that of the absorbing layer 6a. on the other hand,
The light passing through the active layer 4b spreads to some extent and also spreads to the first upper layer 5b. Therefore, when light enters the absorption layer 6a from the active layer 4b, reflection occurs at a constant rate.

■Also, the light incident on the absorption layer 6a from the active layer 1i4b spreads as the thickness of the absorption layer 6a increases, but due to the shape of the absorption layer 6a, whose thickness gradually decreases as it moves away from the side wall surface, it passes through the absorption layer 6a. The light is transmitted through the absorption layer 6a and the second
Reflection occurs at the interface with the upper layer 7a.

etc. are possible.

The present invention has been made in view of such conventional problems, and is an optical semiconductor device capable of efficiently transmitting light by reducing reflection of light at junctions between waveguide layers of each optical semiconductor element. The object of the present invention is to provide a method for producing the same.

Means for Solving Section C] The above problem is firstly achieved by firstly providing first and second guides whose end faces are adjacent to each other on a substrate and having a refractive index larger than the refractive index of the substrate. a waveguide layer; and an upper layer that covers the first and second waveguide layers and has a refractive index smaller than the refractive index of the first and second waveguide layers; The thickness ratio t2/t1 of the thickness t2 of the second waveguide layer to the Wi and thickness Ll of the first waveguide layer is 1/3 or more,
and 3 or less, and secondly, a first waveguide layer having a refractive index larger than the refractive index of the substrate on the substrate; forming a first upper layer having a refractive index smaller than that of the waveguide layer, and selectively removing the first upper layer and the first waveguide layer to remove the substrate. a second layer having a refractive index larger than the refractive index of the substrate, on the exposed substrate and adjacent to the remaining first upper layer and the first waveguide layer; The thickness ratio t 2/l 1 of the thickness t2 of the second waveguide layer to the thickness L1 of the first waveguide layer in the adjacent portion is 1/3 or more, and 3
a step of forming the first upper layer as follows;
forming a second upper layer having a refractive index smaller than the refractive index of the first and second waveguide layers so as to cover the first and second waveguide layers. This is achieved by a method of manufacturing the device.

[Effect]

FIGS. 3(a) and 3(b) are diagrams showing the analysis results obtained from the inventor's considerations to explain the effects of the present invention.

The adjacent portion between the waveguide layers used as a model for this analysis has a configuration as shown in FIG. 3(b).

That is, 11 is formed on the substrate 10 made of InP and has a refractive index of 3.2. M thickness 0. L5ttm, PL emission wavelength 1
．． A guide layer made of Ga1nAsP with a thickness of 1 pm, and a stop layer 12 made of InP with a refractive index of 3, 5, . Film thickness (t
1) 0.15μm, PL emission wavelength 1.55μm
an active layer 14 made of Ga1nAsP of m
Adjacent to refractive index 3.43. PL emission wavelength 1.43
An absorption layer I5 made of Ga1nAsP with a thickness of μm is formed. Furthermore, these layers 14.15 have a refractive index of 3.098.
It is covered with an upper layer I6 consisting of rnP. Here, the absorption layer I5 has a width of about I in contact with the side wall surface of the active layer 14.
The film thickness is the thickest in the adjacent part of 0 μm, gradually decreases as it moves away from the side wall surface, and becomes constant again at a film thickness of 0.15 μm beyond about 50 μm from the side wall surface.

The analysis is based on the change in the thickness ratio t2/l1 of the thickness L2 of the absorption layer 15 to the thickness t1 of the active layer 14 on the side wall surface in such a configuration. We investigated the proportion of light with a wavelength of 1.55 μm that is reflected and no longer transmitted.

According to the analysis results, as shown in Figure 3(a), the reflection rate begins to increase rapidly when the film thickness ratio exceeds 2.8, and becomes considerably large at over 6X10-' when the film thickness ratio exceeds 3. Become.

From the above results, light can be efficiently transmitted if the thickness ratio of the absorbing layer 15 to the active layer 14 is set within three times.

It hit me. It is thought that this result can be similarly applied to the connection between the first and second waveguide layers, which transmits light in a -C manner and has a film thickness comparable to that of the analytical model. If the film thickness ratio t2/t1 of the connection part between the connection part film thickness tl) and the second waveguide layer (connection part film thickness 12) is kept in the range of 1/3 to 3, light can be efficiently It will be possible to convey the following.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(d) is a cross-sectional view of the configuration of an optical semiconductor integrated circuit device according to a first embodiment of the present invention, and FIG.
A top view of the configuration is shown.

In FIG. 1(e), 27 is a light generating section formed on the common substrate 20, 28 is a light modulating section provided adjacent to the light generating section 27, and 26a is an active layer of the light generating section 27. 21b
One electrode is used to supply current to the active layer 21b, and the supplied current can generate laser light from the active layer 21b. Reference numeral 26b denotes one electrode of the light modulation section 28 for applying a voltage to the absorption layer 23a, and the applied voltage can tilt the energy band of the absorption layer 23a and change the light absorption rate. ing.

Note that a common electrode 30 is provided on the back surface of the common substrate 20 as the other electrode.

In FIG. 1(d), 17 is a common substrate made of InP, and 18 is a substrate with a refractive index of 3.2.
19 is a guide layer 18 made of common Ga1nAsP with a film thickness of 0.15 μm and a PL emission wavelength of 1.1 μm.
The guide layer 19 and the stop layer 19 constitute a common substrate 20, which is a stop layer made of InP with a film thickness of about 200 nm for stopping etching during the fabrication of the device. Moreover, 21b is selectively provided on the stop layer 19 and has a refractive index of 3.5. Film thickness: 0.15 μm, PL emission wavelength: 1.55.
The active layer (first waveguide layer) made of c+m Ga1nAsP, 22b is the first upper layer made of InP with a refractive index of 3.098 and a film thickness of 1〃m, which is overlaid on the active layer 21b. , the active layer 21b and the first upper layer 22b have one continuous sidewall surface.

Furthermore, 23a is provided adjacent to the side wall surfaces of the active layer 21b and the first upper layer 22b, and has a refractive index of 3.43. P
An absorption layer (second waveguide layer) made of Ga1nAsP with an L emission wavelength of 1.43 μm, 24a has a refractive index of 3.0 and covers the active layer 21b, first upper layer 22b, and absorption layer 23a.
98 second upper layer. Note that the first and second upper layers 22b and 24a constitute one upper layer 25.

Here, it is ideal that the thickness of the absorption layer 23a is made to completely match the thickness (tl) of the active layer 21b while maintaining a uniform thickness. Control is difficult due to the manufacturing method of forming a film by phase epitaxy (MOCVD).

However, the film thickness (L2) of the absorption layer 23b along the side wall surfaces of the active layer 21b and the first upper layer 22b is reduced to a film thickness ratio of L2/11.
By adjusting the ratio to 1/3 to 3, Figure 3 (a
According to the inventor's considerations shown in ), it is possible to gradually reduce the reflection of incident light at the adjacent portion.

In the case of the example, for example, the absorption layer 23b has a film thickness [t2] of about 0.4 μm along the side wall surface, and the film thickness gradually decreases as it moves away from the side wall surface, and the thickness [t2] from the side wall surface is about 50 μm.
The film thickness is constant at 0.13 μm beyond m.

Next, a method for manufacturing such an optical semiconductor integrated circuit device will be described with reference to FIGS. 1(a) to 1(e).

FIGS. 1(a) to 1(e) are cross-sectional views illustrating a method for manufacturing an optical semiconductor device according to a second embodiment of the present invention.

First, as shown in the same figure (a), a base 1 made of rnP
7 with a refractive index of 3.2. Film thickness: 0.15 μm.

A guide layer 18 made of Ga1nAsP with a PL emission wavelength of 1.1 μm, a stop layer 19 made of InP with a refractive index of 3.098 and a film thickness of about 200 μm, and a refractive index of 3.5, ll.
Thickness (tl) approximately 0.15 μm, P L emission wavelength 1.
An active layer (first waveguide layer) 21 made of Ga1nAsP with a thickness of 55 μm and an In layer with a refractive index of 3.098 and a film thickness of 1 μm.
The first upper layer 22 made of P is formed by liquid phase epitaxial (
LPE) method. Note that the base body 17. Guide layer 18 and stop layer 19 constitute a common substrate 20 .

Next, as shown in FIG. 6B, the first upper layer 22 is etched with hydrochloric acid using a resist pattern (not shown) as a mask, and then the etching is stopped at the underlying stop layer 19 using the same resist pattern as a mask. The active layer 21 is heated to H2S until
Selective etching is performed using a mixed solution of o, /H, and O□/H2O, respectively.

Next, the film thickness (t2) on the side wall surface of the absorbing layer formed along the side wall surfaces of the active layer 21a and the first upper layer 22a is adjusted such that the film thickness ratio t2/l1 is 1/3 to 3. At the same time, in order to prevent the thickness of the absorption layer from becoming too thin away from the side wall surface, as shown in the top view of FIG. The groove 32 in the SiO2 film 31 is formed so that the width of the plane region where the layer is to be formed becomes narrower as it goes away from the side wall surface.

Next, as shown in FIG. 1(c), the first layer is grown on the exposed stop layer 19 by selective growth using the LPE method.
The active layer 2 is adjacent to the upper layer 22a and the active layer 21a.
The same material as 1a, but a different composition with a refractive index of 3.434,
An absorption layer (second waveguide layer) 23 made of GaTnAsP with a P L emission wavelength of 1.43 μm is formed. At this time, the absorption layer 23 formed by the grooves 32 of the SiO□ film 31 is formed thinner than usual at 0.3 μm in film thickness along the side wall surfaces of the first upper layer 22a and the active layer 21a.
The film thickness gradually decreases as it moves away from the side wall surface, and the cross-sectional shape becomes such that the film thickness is approximately constant at 0.15 μm beyond about 40 μm.

Next, after removing the Sing film 31, a second upper layer 24 made of InP forms the active layer 21a and the first upper layer 22.
Next, as shown in the top view of FIG. 2(b), the active layer 21a and the adjacent absorbent layer 23 are buttered together with the first upper layer 22a and the second upper layer 24. , forming successive waveguide layers approximately 1.5 μm wide with different compositions.

Next, by selective growth using the LPE method, a high-resistance buried layer 24b made of InP is formed by covering the first upper layer 22b, the active layer 21b, the absorption layer 23a, and the second upper layer 24a. . After that, the second layer on the active layer 21b
When electrodes 26a and 26b are formed on the surface of the upper layer 24a and the surface of the second upper layer 24a on the absorption layer 23a, a light generation section 27 including the active layer 21b and a light modulation section 28 including the absorption layer 23b are formed. Optical semiconductor integrated circuit device is completed (
Figure (d)).

In the optical semiconductor integrated circuit device thus produced, the absorption edge wavelength of the absorption layer 23a, 1.43 μm, is shorter than the absorption edge wavelength of the active layer 21b, 1.55 μm. Therefore, when a current is injected into the light generating section 27 to cause light with uniform intensity to be incident on the absorption layer 23a of the light modulation section 28 from the active layer 21b, when no voltage is applied to the absorption layer 23a, the incident light is Light passes through the absorption layer 23a with almost no absorption, but when the voltage applied to the light modulator 28 is changed, the energy band of the absorption layer 23a is tilted and the wavelength of the effective absorption edge changes, which increases the absorption of light. The proportion of

In this way, a signal is generated by changing the intensity of light passing through the absorption layer 23a.

According to the embodiment of the present invention as described above, as shown in FIG. /11 is 1
/3 to 3, the ratio of reflection of light transmitted from the active layer 21b to the absorption layer 23a is reduced to effectively transmit light, as shown in the analysis results in FIG. I can do it.

In the embodiment of the present invention, the active layer 21b of the light generation section 27 and the absorption layer 23a of the light modulation section 28 are used as the first and second waveguide layers, but the present invention is not limited to this. It can also be applied to connections between waveguide layers having different compositions.

In addition, for the connection portion between waveguide layers having different compositions in an optical semiconductor device using semiconductor materials in which the film thickness and refractive index of each layer constituting the optical semiconductor device of the present invention are similar to those of the above embodiments. The present invention can also be applied to.

〔Effect of the invention〕

As described above, according to the optical semiconductor integrated circuit device and the manufacturing method thereof of the present invention, the film thickness ratio at the connection portion of the first and second waveguide layers sandwiched between the layers having a low refractive index is 1/ 3～3
Therefore, the ratio of reflection of light passing between the waveguide layers can be reduced and light can be transmitted effectively.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a method for manufacturing an optical semiconductor integrated circuit device according to an embodiment of the present invention; FIG. 2 is a top view illustrating a method for manufacturing an optical semiconductor integrated circuit device according to an embodiment of the present invention; FIG. 3 is an explanatory diagram of the operation and effect of the present invention, and FIG. 4 is an explanatory diagram of a conventional method of manufacturing an optical semiconductor integrated circuit device. [Explanation of symbols] 1.10.17... Base body, 2.11.18... Guide layer, 3.12.19... Stop layer, 4.4a, 4b... Active layer, 5. 5 a, 5 b, 22.22a, 22b - first upper layer, 6.6a... absorption layer, 7.7a, 24.24a... second upper layer, 7b, 2
4b...High resistance buried layer, 8.16.25... Upper layer, 9a, 9b, 26a, 26b, 30-
Electrode, 13.20...Substrate, 14, 21, 21a, 21b-...Active layer (first
waveguide layer), 15.23.23a... absorption layer (second waveguide layer),
27... Light generation section, 28... Light modulation section, 31... SiO□ film, 32... Groove.

Claims (2)

[Claims] (1) first and second first and second substrates whose ends are adjacent to each other on a substrate and have a refractive index greater than the refractive index of the substrate;
a waveguide layer, and an upper layer covering the first and second waveguide layers and having a refractive index smaller than the refractive index of the first and second waveguide layers; The film thickness t2 of the second waveguide layer with respect to the film thickness t1 of the first waveguide layer at
An optical semiconductor device characterized in that the film thickness ratio t2/t1 is 1/3 or more and 3 or less. (2) on a substrate, a first waveguide layer having a refractive index greater than the refractive index of the substrate; and a first upper layer having a refractive index smaller than the refractive index of the first waveguide layer; selectively removing the first upper layer and the first waveguide layer to expose the substrate; 1 and adjacent to the first waveguide layer, a second waveguide layer having a refractive index larger than the refractive index of the substrate is formed so as to have a film thickness t3 of the first waveguide layer in the adjacent portion. said second for
forming the waveguide layer so that the film thickness ratio t2/t1 of the film thickness t2 is 1/3 or more and 3 or less, the first upper layer, the first and second waveguide layers; forming a second upper layer having a refractive index smaller than the refractive index of the first and second waveguide layers so as to cover the first and second waveguide layers.