JPH0269703A - Branch type optical waveguide - Google Patents

Abstract

PURPOSE:To eliminate a decrease in propagation efficiency due to scattering loss by forming optical waveguide layers of a II-VI compound semiconductor which has a large refractive index and forming at least one of the layers by selective epitaxial growth. CONSTITUTION:An SiO2 film vapor-deposited on a GaAs substrate 11 and then removed at a part where the optical waveguide is formed by a photolithographic process to form a mask. Then, a lower clad layer 12, an optical waveguide layer 13, and an upper clad layer 14 are grown selectively in order. In this selective growth, the II-VI compound semiconductor is grown selectively epitaxial growth only at the part where the mask of the SiO2 film is not present. Thus, a double hetero joining type optical waveguide structure is grown selectively and then the SiO2 film of the mask is removed to complete the II-VI compound semiconductor branch type optical waveguide. Consequently, the surface roughening etc., of the waveguide area due to etching, etc., is prevented and a decrease in scattering loss is therefore reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compound semiconductor optical waveguide used as a component of an optical integrated circuit or an optoelectronic integrated circuit.

[Conventional technology 1 Conventional optical waveguides (including branched optical waveguides) have a diameter of 1.0 μm.
For the purpose of guiding light in the m and 1.3 μm wavelength bands, AlGaAs/GaAs system or InGaAsP
/InP-based III-V compound semiconductors. Figure 5 shows the applied physics
Letter (Appl, Phys.

Lett, l 47, 186 (19851) In an optical waveguide, a cladding layer (22) made of AI GaAs (22) of high purity GaAs (carrier concentration 10"cm-") (23) was sequentially laminated on a GaAs substrate (21). , forming ribs by etching.High purity of GaAs reduces free carrier absorption, and AlGaAs
This prevents light from leaking to the substrate side, resulting in a low propagation loss value.

[Problems to be Solved by the Invention] However, since the optical waveguide of the above-mentioned prior art is formed of a III-V group compound semiconductor, the energy gap is close to or even greater than that of the crystal forming the optical waveguide layer. When trying to guide light with large photon energy, the absorption loss was large and the propagation efficiency was low.

Furthermore, since the optical waveguide was formed by etching after epitaxially growing the double heterojunction, surface roughness due to etching could not be avoided, resulting in a reduction in propagation efficiency due to scattering loss. Moreover, since the waveguide was formed through a long process, the yield would ultimately be low.

The present invention is intended to solve these problems, and its purpose is to manufacture a branched optical waveguide with low absorption loss through a simple process and with high yield.

[Means for Solving the Problems] The branched optical waveguide of the present invention is a branched optical waveguide in which optical waveguides are branched or merged at one or more force points, and the optical waveguide has at least a group II-VI group on a substrate. It has a cladding layer made of a compound semiconductor and an optical waveguide layer made of a 1l-VI group compound semiconductor having a larger refractive index than the cladding layer,
At least one of the above layers is selectively epitaxially grown.

Embodiment FIG. 1 is a top view and a sectional view of a branched optical waveguide made of a II-VI group compound semiconductor in an embodiment of the present invention.

The difference from the conventional example is that the optical waveguide is made of a II-VI group compound semiconductor.

1 is a GaAs substrate, 2 is a lower cladding layer made of ZnS, 3 is an optical waveguide layer made of Zn5e, and 4 is an upper cladding layer made of ZnS. The refractive indices of Zn5e and ZnS are 2.34 and 2.31, respectively, and light is effectively confined in the direction perpendicular to the interface due to this large refractive index step, and also in the direction parallel to the interface, with a refractive index of 2.34. Since the Zn5e optical waveguide layer is sandwiched between the atmosphere having a refractive index of 1.0, light is sufficiently confined within the waveguide.

Below, the manufacturing process of the branched optical waveguide of the present invention will be explained step by step with reference to FIG.

First, a GaAs substrate (1) is prepared, and a monosilane (Si)
A SiO□ film is deposited on the substrate by a thermal CVD method using Hu) as a raw material.The SiO□ film is then removed by a photolysylgraph process to form a mask. (FIG. 2(a)) Next, the lower cladding layer (2), the optical waveguide layer (3), and the upper cladding layer (4) are selectively grown in this order. ZnS and Z were grown by metal organic chemical vapor deposition (MOCVD) using organic metals such as dimethylzinc (DMZn) as a zinc source, dimethylsulfur (DMS) as a sulfur source, and dimethylselenium (DMSe) as a selenium source as raw materials. The n Se heterojunction is formed by switching the pulps in the dimethyl selenium and dimethyl sulfur gas lines while dimethyl zinc is flowing. The growth conditions are a growth pressure of 100 Torr or less, a growth temperature of 400° C. or more and 700° C. or less, and (2) a raw material supply ratio of iron raw material and Group II raw material of 6 or less. Although the explanation has been made using methyl derivatives such as dimethylzinc as the raw material used, it is also possible to use ethyl derivatives such as diethylzinc and other alkyl metal compounds. In the selective epitaxial growth described above, the SiOg film serves as a mask, there is no deposit on the mask, and the It-VI group compound semiconductor is epitaxially grown selectively only in the areas where there is no mask.

After selectively growing a double heterojunction optical waveguide structure as described above, when the mask SiO□ film is removed, the I
The I-Ml group compound semiconductor branched optical waveguide is completed.

In the branched optical waveguide of the present invention, the optical waveguide is made of an H-VI group compound semiconductor having a large energy gap. Therefore, absorption and loss during waveguiding can be kept small. Further, since the SiOx of the mask is only removed after epitaxial growth of the waveguide layer, surface roughness caused by etching of the waveguide region can be prevented, which greatly contributes to reducing scattering loss.

In addition, in the description of the embodiment, it has a double heterojunction structure of a lower cladding layer, an optical waveguide layer, and an upper cladding layer, and a refractive index step is obtained by sandwiching the optical waveguide layer in the atmosphere in the direction parallel to the interface. Although the description has been made using a branched optical waveguide having a structure as shown in FIG. 1, the branched optical waveguide of the present invention can also be realized by a waveguide structure as shown in FIG.

(a) is a simpler type in which the upper cladding layer is omitted, and (b) is a type in which the side surfaces of the optical waveguide layer are embedded with ZnS, which requires more steps but exposes the side surfaces of the waveguide to the air. The width of the waveguide at which the first mode of the guided light is cut off can be made wider than in the case where the first mode of the guided light is cut off, and the workability of the process is improved. (C) uses a 5ift insulating film instead of a compound semiconductor as the constituent material of the upper cladding layer, and has a refractive index of 5iO = (1,4) and a Zn5
Light is confined due to the difference in refractive index of e.

In addition, as a combination of optical waveguide layer and cladding layer, Z
Optical waveguides can be formed using not only the n5e-ZnS system but also the combinations shown in the table below. The formation method is based on the MOCVD method using an organic compound of the relevant element.

FIG. 4 shows an application example of the optical waveguide of the present invention. In Figure 1, the angle θ of the branching of the output side waveguide was kept the same (θ1=
02), in this case, assuming that there is no propagation loss, for an input light of 1, the output light of each waveguide is both 0 and 5.
Met. However, if 01≠02 as shown in FIG. 4(a), the ratio of the output lights of the two output waveguides is no longer l. By changing the values of θ3 and θ2, the ratio of the output from one waveguide to the input light can be set to any value between 0 and 1. Furthermore, if only one output side waveguide is used, it functions as an optical filter.

Figure 4(b) shows a combination of two or more branched optical waveguides according to the present invention, in which the input lights ■, ■, ■ are repeatedly separated and combined in the optical waveguide, and the output lights ■, ■, ■. This is a schematic representation of what can be obtained.

[Effects of the Invention] As described above, the branched optical waveguide of the present invention has the following effects.

(1) II-V optical waveguide with large energy gap
Since it is formed of a T group compound semiconductor layer, it is possible to shorten the wavelength of guided light. Furthermore, due to the wide energy gap of II-VI compound semiconductors, even when light in the same wavelength range as conventional ones (1 μm band, 1.3 μm band) is guided, the absorption loss in the optical waveguide is significantly lower than that of conventional ones ( Being held down.

The branched optical waveguide of the present invention can guide even light with a short wavelength of 600 nm with extremely low propagation loss.

(2) Since the optical waveguide is formed by selective growth, there is no need to perform processes such as etching or diffusion after growth.
This can prevent deterioration in film quality or surface roughness in subsequent steps, and as a result, it is possible to reduce scattering loss.

(3) By changing the angle of the output side optical waveguide, the incident light can be split into two or more directions at an arbitrary ratio.

Also, if only one side of the output waveguide is used, it becomes an optical filter.

(4) Since the MOCVD method is used as a means for growing the optical waveguide, control of film thickness and reproducibility are improved.

Furthermore, compared to other growth methods, it is possible to increase the area of the wafer, making it suitable for mass production.

(5) Since the process is extremely simple and short, the yield is improved. In particular, when forming a monolithic array on the same substrate as other devices such as a semiconductor laser, a simple process and high yield are advantageous conditions, and this indicates that it has high potential for monolithic fabrication.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are top and cross-sectional views of a branched optical waveguide showing an embodiment of the present invention. FIGS. 2(a) to 2(c) are cross-sectional views showing the manufacturing process of the present invention. FIGS. 3(a) to 3(c) are sectional views showing other embodiments of the present invention. FIGS. 4(a) and 4(b) are top views showing an application example of the present invention. FIGS. 5(a) and 5(b) are a top view and a sectional view of a branched optical waveguide showing a conventional example. 23...GaAa optical waveguide layer 24...Input light 25...Output light Applicant Seiko Epson Co., Ltd. agent Patent attorney Masayoshi Kamiyanagi (1 other person), substrate, lower cladding layer, optical waveguide layer・Upper cladding layer・Mask (S i Ox film) ・Upper cladding layer (SiO− ・GaAs substrate ・AlGaAs cladding layer film) (ku) Ha′ (υ) (b) (b) A′ (C/) (to (lx,) (ω (ku) (1o)

Claims (1)

[Claims] In a branched optical waveguide in which optical waveguides branch or merge at one or more locations, the optical waveguide has at least II-
It has a cladding layer made of a group VI compound semiconductor, and an optical waveguide layer made of a group II-VI compound semiconductor having a higher refractive index than the cladding layer, and at least one of the layers is selectively epitaxially grown. Branch type optical waveguide.