JPH0677596A - Optical functional element - Google Patents

Abstract

PURPOSE:To provide an element having a laminated waveguide structure which is used for an optical functional element having a filter, a plurality of optical waveguides such as a filter and a demultiplexer. CONSTITUTION:A plurality of waveguides 103, 106 having quantum well structures are formed perpendicularly on a semiconductor substrate 101. The waveguides 103, 106 are laterally confined by diffusing an impurity, implanting impurity ions and heat treating to crystal-mix a clad part extended in parallel direction with the substrate 101. Semiconductor materials 109 having different impurity diffusing speeds are selectively disposed in parallel with the substrate 101, thereby forming the plurality of the waveguides 103, 106 with high degree of designing freedoms.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical functional device having a laminated optical waveguide structure used for an optical functional device having a plurality of optical waveguides such as filters and demultiplexers.

[0002]

2. Description of the Related Art Conventionally, it is widely known that a low-loss waveguide can be realized by using a quantum well structure for an optical waveguide. It is also known to form a flat waveguide by utilizing the fact that the quantum well structure is disordered by impurity diffusion or heat treatment.

On the other hand, when arranging optical functional elements such as a filter, a laser and an amplifier on the same substrate, it is obvious that high integration can be achieved by arranging them three-dimensionally. As a method of manufacturing a three-dimensional waveguide, there is a method of manufacturing a ridge type or a buried type waveguide.

[0004]

However, in the ridge type of the three-dimensional waveguide, the wafer surface becomes considerably uneven, and the pattern may be disturbed when an electrode or the like is formed after the waveguide is formed. Further, the embedded type requires a selective growth technique, and its characteristics may impose design restrictions in terms of the mask portion area and the like.

Furthermore, a method has been proposed in which a waveguide is formed by a quantum well structure and lateral confinement of the waveguide is made by mixed crystal. When this method is used, the wafer surface is flat, but the laminated waveguide is used. When forming the structure, the other waveguide on the back surface side of the substrate can be formed only at the position where the waveguide is formed on the front surface side of the substrate, and the degree of freedom in designing the laminated waveguide structure is poor.

Therefore, an object of the present invention is to provide an optical functional element which can realize a flat laminated waveguide structure having a high degree of design freedom in order to solve the above problems.

[0007]

According to the present invention for achieving the above object, a plurality of waveguides are provided in a direction vertical to a substrate, and the waveguides have a quantum well structure. A waveguide in which lateral confinement is performed by the mixed crystal of the clad portion extending in the parallel direction by impurity diffusion (or by impurity ion implantation and heat treatment),
By selectively arranging materials with different impurity diffusion rates in the direction parallel to the substrate, the diffusion region is controlled, and a flat waveguide having a high degree of freedom in designing the waveguide is formed. Here, materials having different impurity diffusion rates may be arranged between a plurality of waveguides existing in the direction perpendicular to the substrate. Further, materials having different impurity diffusion rates are Al _x Ga _1-x As (x <0.
2) and Al _x Ga _1-x As (x> 0.4), and the impurity may be Zn. Further, the substrate and the waveguide may be a III-V group compound semiconductor.

More generally, in the optical functional device according to the present invention which achieves the above object, a plurality of waveguides having a quantum well structure arranged in a direction perpendicular to the substrate and a mixed crystal for laterally confining the waveguides. And a portion formed by selectively arranging a semiconductor material having a different impurity diffusion rate in a direction parallel to the substrate and selectively disposing the semiconductor material portion having a different impurity diffusion rate. Thus, the mixed crystal portion is formed in a desired shape, and the plurality of waveguides are formed in a desired arrangement.

[0009]

By using the above means, a flat waveguide can be formed. Further, in addition to the position where the substrate front surface side waveguide is formed, the substrate rear surface side waveguide can be formed at a position protected by a material having a low impurity diffusion rate, which increases the design freedom of the waveguide.

The present invention utilizes the following principles. For example, G
Al _x Ga _1-x As on the aAs substrate using MOCVD
(X = 0.0, 0.2, 0.4, 0.6, 0.8) was deposited. Next, ZnO is deposited on the surface of the substrate, and 60
It heated at 0 degreeC for 1 hour, and measured the density | concentration of Zn by SIMS (secondary ion mass spectrometry). The depth at which the Zn concentration is 1 × 10 ¹⁹ or more is defined as the Zn diffusion depth. Al _x
FIG. 2 shows the relationship between the Zn diffusion rate and the Ga _1-x As composition ratio x. Thus, the diffusion rate becomes faster as the composition ratio x becomes larger. Therefore, the Al composition ratio x
Is used as the diffusion control layer, the mixed crystal aspect of the waveguide portion of the quantum well structure can be controlled with a high degree of freedom, and a plurality of types of waveguide structure regions can be created with a high degree of design freedom.

[0011]

[Embodiment 1] Hereinafter, with reference to FIG. 1, a description will be given of a manufacturing process of an embodiment 1 of an optical functional element having a laminated waveguide structure manufactured according to the present invention.

In FIG. 1, on a GaAs substrate 101,
A cladding layer (A1 _0.5 Ga _0.5 As) 102, a first waveguide layer (which is an MQW (multiple quantum well) layer) 103, a cladding layer (A1 _0.5 Ga _0.5 As) 104, a diffusion control layer (Ga).
As) 109 is deposited, and the diffusion control layer 10 is formed only in the region 1.
9 is left, and the diffusion control layer in the other region is removed. Next, the cladding layer (A1 _0.5 Ga _0.5 As) 105, the second waveguide layer (MQW) 106, the cladding layer (A1 _0.5 Ga _0.5 As)
Deposition is performed in the order of 107 using the MOCVD method. And
The SiN _x 110 is deposited as a mask on it, as shown in FIG. 1, removing the SiN _x 110 other than the region 3. After that, ZnO 108 is deposited as a diffusion source.

The wafer thus produced is heated in an Ar atmosphere to form a Zn diffusion region 301 as shown in FIG. 3, and the MQW portions 103 and 106 other than the mask portion are mixed crystallized.

In the region 1, there can be a waveguide below the diffusion control layer 1.9, in region 2 no waveguide, and in region 3 there can be an upper and lower waveguide below the SiN _x mask 110. As described above, according to the present invention, three types of waveguide structure regions can be created with a high degree of freedom in design.

[0015]

Second Embodiment Next, with reference to FIG. 4, a laminated directional coupler manufactured according to the present invention will be described.

In FIG. 4, on the GaAs substrate 401,
There is a first MQW waveguide 403 sandwiched between two A1 _0.5 Ga _0.5 As clads 402 and 404, and a second MQW waveguide 407 sandwiched between the other two A1 _0.5 Ga _0.5 As clads 406 and 408. There is a certain B region and an A region on the diffusion control layer 411 that is mixed crystallized. In the B area,
The grating section 4 is provided between the MQW waveguides 403 and 407.
05 is formed.

Here, the light incident from FIG. 4 is split into a TE wave propagating in the MQW waveguide 403 and a TM wave radiating to the mixed crystal region in the A region, and then in the B region, the grating portion. The wavelengths coupled to the second MQW waveguide 407, which are determined by the structure 405, are output to and the light of other wavelengths are output to.

In this way, a flat laminated directional coupler can be produced by growing the entire surface twice. In addition, in FIG.
Reference numeral 409 is a SiN _x diffusion mask, and 410 is a diffusion region.

[0019]

Third Embodiment Next, with reference to FIG. 5, a semiconductor laser produced by the present invention will be described.

In FIG. 5, n-A1 _0.45 Ga _0.55 As cladding 502, A1 is formed on an n-GaAs substrate 501.
_0.1 Ga _0.9 As active layer 503, p-A1 _0.45 Ga _0.55 A
s504, GaAs cap layers 505 and 506 are deposited, and the GaAs cap layer 50 other than the active region is deposited.
Remove 5,506. Next, the GaAs cap layer 5
The diffusion control layers 05 and 506 were used to diffuse Zn over the entire surface to form a diffusion region 508 and a low resistance diffusion region 506. In addition, 507 and 509 are electrodes. The oscillation of the semiconductor laser produced as described above was confirmed.

As described above, a flat low resistance semiconductor laser could be formed by one-time whole surface growth and one-time whole surface diffusion.

[0022]

[Embodiment 4] A waveguide prepared according to the present invention will be described below with reference to FIG.

In FIG. 6, the first waveguide 60 in plan view is shown.
The first, second, and third waveguides 602 and 603 are arranged (FIG. 6A), and the second waveguide 602 and the third waveguide 603 are laminated and arranged in a sectional view (FIG. 6A). 6 (b)).
6B, 604, 608, 609, 6
10 is the diffusion region 301, layers 108, 109, and
Each waveguide 60 is a part that performs the same function as 110.
1, 602 and 603 are sandwiched by clad layers.
Here, the lights incident from the waveguides 601 and 602 side are demultiplexed into the first waveguide 601 and the second waveguide 602, respectively. Next, the specific wavelength of the light branched to the second waveguide 602 is coupled to the third waveguide 603 (this portion is a laminated directional coupler) and emitted from the side.

As described above, according to the present invention, it is possible to form a flat three-dimensionally arranged waveguide.

[0025]

According to the present invention, a flat laminated waveguide having a high degree of design freedom can be produced. Further, the present invention has the following effects. 1) Since the laminated waveguide can be formed with a high degree of freedom, filters, amplifiers, and detectors can be formed three-dimensionally on the same substrate, and high integration is possible. 2) The waveguide shape can be designed relatively freely regardless of crystal anisotropy. 3) Since the lateral confinement of light is not as strong as in the embedded type (the lateral confinement is performed in the diffusion region), the loss is small. 4) Since the state of confinement differs depending on the TE and TM waves, it can have a function as a polarization mode filter.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a diffusion control layer arrangement according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an experimental result regarding the principle of the present invention.

FIG. 3 is an explanatory diagram showing a waveguide arrangement according to the first embodiment of the present invention.

FIG. 4 is a configuration diagram of a laminated directional coupler that is Embodiment 2 of the present invention.

FIG. 5 is a configuration diagram of a semiconductor laser that is Embodiment 3 of the present invention.

FIG. 6 is a configuration diagram of a duplexer that is Embodiment 4 of the present invention.

[Explanation of symbols]

101 GaAs substrate 102 Cladding layer 103 First waveguide layer 104 Cladding layer 105 Cladding layer 106 Second waveguide layer 107 Cladding layer 108,608 ZnO 109,609 Diffusion control layer 110,610 SiN _x 301 Diffusion region 401 GaAs substrate 402 Cladding Layer 403 First waveguide 404 Cladding layer 405 Grating portion 406 Cladding layer 407 Second waveguide 408 Cladding layer 409 SiN _x diffusion mask 410 Diffusion region 411 Diffusion control layer 501 n-GaAs substrate 502 Cladding layer 503 Active layer 504 Cladding layer 505 Cap layer 506 Low resistance layer (cap layer diffusion region) 507 Electrode 508 Diffusion region 509 Electrode 601 First waveguide 602 Second waveguide 603 Third waveguide 604 Diffusion region

Claims (6)

[Claims] 1. A plurality of waveguides are provided in a direction perpendicular to a substrate,
The waveguide has a quantum well structure, and the waveguide is laterally confined by clad portions extending in a direction parallel to the substrate being crystallized by impurity diffusion or impurity ion implantation and heat treatment. A semiconductor material having different impurity diffusion rates is extended in a direction parallel to the substrate and selectively arranged to form the mixed crystallized portion in a desired form to form a plurality of waveguides in a desired arrangement. Optical function element to be. 2. The optical functional element according to claim 1, wherein the materials having different impurity diffusion rates are arranged between a plurality of waveguides existing in a direction perpendicular to the substrate. 3. The optical functional device according to claim 1, wherein the impurity is Zn or Si. 4. The optical functional device according to claim 1, wherein the substrate and the waveguide are III-V group compound semiconductors. 5. The quantum well structure is GaAs or A
The semiconductor materials composed of ₁ GaAs and having different impurity diffusion rates are Al _x Ga _1-x As (x <0.2) and Al _x Ga _1-x As (x> 0.4). The optical function element according to claim 1. 6. A plurality of waveguides arranged in a direction perpendicular to a substrate and having a quantum well structure, a mixed crystallized portion for lateral confinement of the waveguides, and a semiconductor material having different impurity diffusion rates in a direction parallel to the substrate. And a portion formed by selectively arranging the semiconductor material portions having different impurity diffusion rates, and by appropriately arranging the semiconductor material portions having different impurity diffusion rates, the mixed crystal portion is formed in a desired form. The optical functional element is characterized in that the waveguide is formed in a desired arrangement.