JPS604961B2 - optical waveguide device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical waveguide device in an optical integrated circuit, etc.
An oxide single crystal with an AB04-type regular crystal structure such as Mo04 is used as a substrate, and a low group cubic compound semiconductor thin film such as ZnTe, ZnSe, or a mixed crystal thereof is bonded to the substrate to form an optical waveguide. The purpose of this invention is to form an optical waveguide device for use in various optical integrated circuit functional elements.

Future high-capacity optical communication systems will include a variety of active and passive integrated optical circuit devices capable of guiding and processing information-carrying light waves.

Recently, various thin film optical waveguides and optical integrated circuits have been studied for this purpose.

Based on research in this field to date, the success of such optical systems depends on the development of thin film materials with suitable light transmission properties and suitable for the fabrication of devices with waveguide processing.
Currently, single-crystal thin film materials generally have low optical waveguide loss, are easy and inexpensive to manufacture with desired properties and shapes, and are well suited for the production of active devices. For example, Lj
Nb03, GaAs-GaAIAs, various garnet thin film single crystals, etc. have been studied, and devices such as thin film optical switches, modulators, and lasers have been reported. However, despite these recent developments and studies, single crystal materials suitable for optical thin film devices are rare in terms of optical loss, modulation, etc. Therefore, there is an increasing demand today for new single crystal materials suitable for the fabrication of many types of active and passive components in said optical systems. By the way, Rhoch group compound semiconductors have a large electro-optic effect among semiconductors, and there are reports of optical modulators using single crystal plates of ZnSe and ZnTe.

However, there are no examples of thin film single crystals, and it is simply ZnTe-G.
There is only one example of a single crystal thin film being created as a semiconductor heterojunction, such as in the A ship, and this ZnTe-GaAS is
ZnT is suitable for optical devices because its refractive index is higher than that of AS.
It is not possible to trap light in the e-crystal, and it cannot be used as an optical waveguide device. Therefore, the present invention is based on the boss ZnSe.
, ZnTe, etc. are used, and this single crystal thin film is generally of the AB04 type (where A is Pb, Ca, Sr, B
One selected from a, B is Mo, one selected from W)
Excellent optical transmission characteristics can be obtained by forming an optical waveguide on a single crystal thin film formed on a single crystal substrate with a tetragonal horizontal structure. That is, PbM
AB04 with a tetragonal structure such as o04 and CaW04
Until now, oxides of this type have been treated in the form of single crystals or powders, and have been studied as acousto-optic devices and as base materials for crab optics and lasers. This AB04 type crystal has a light refractive index smaller than that of low group compound semiconductors such as ZnTe and ZnSe, and when the above 01 group compound semiconductor single crystal thin film is grown on this A804 type crystal substrate, this thin film It is possible to obtain an excellent optical waveguide in which light is effectively confined, the electro-optic effect is large, and the loss is small. Now, A
The following table shows the crystallographic properties of B04 type crystals and low-choice group semiconductor crystals such as ZnSe, ZnTe, and ZnS. From this table, looking at the junction between the 0- group semiconductor crystal and the A804 type striped crystal, the degree of lattice constant deviation is about 14% or less, which is within the range where epitaxial growth is possible, and in terms of the crystal structure. (001) plane of AB04 type crystal and {1 of semiconductor crystal
00} plane, the best epitaxial growth can be obtained.

Furthermore, the difference in coefficient of thermal expansion of the low W group semiconductor-A804 crystal is smaller than that of Si on sapphire, which is currently successful in epitaxial formation, and the thermal strain due to cooling is small. From the refractive index comparison in the table above, the low W group semiconductor crystal has a higher refractive index than the A804 crystal, and the thickness of the semiconductor crystal thin film is on the order of approximately close to the wavelength of light propagating in the thin film in the guided mode parallel to its plane. When the thickness is large enough, an optical waveguide device for high-quality optical waveguide can be constructed. Originally, a thin film for an optical waveguide only needs to have a thickness on the order of the wavelength of the light propagating therein, and the thickness of the thin film can range from 0.1 of the optical wavelength to ION sound. The wavelength range of 1 to 1 digit is good.

Optical waveguide experiments are carried out by introducing laser light into a thin film using a well-known prism optical coupler as shown in FIG. In FIG. 1, 1 is a substrate, 2 is an epitaxial thin film for optical waveguide, 3 and 3' are prism couplers, and 4 is a laser beam. By this method, it is possible to determine the value of optical loss and determine the quality of the thin film. Now, an embodiment of the present invention will be described in which a rho group semiconductor crystal thin film is obtained by epitaxial growth on the AB04 type crystal.

{1'PbMo04, ZnSe deposition on European W04P
Vapor deposition was performed using the (001) plane of bMo04 as a substrate and a ZnSe single crystal as an evaporation source.

The substrate temperature was varied from 200oo to 600qo, and the deposition temperature was from 800°C to 1000o. A fairly good epitaxial film can be obtained at a substrate temperature of 400 to 500 pm, and the loss is small in the optical waveguide test, and almost the same results can be obtained with Iso W04.

(2) Growth of ZnTe on PbMo04 Using the (001) plane of PbMo04 as a substrate, vapor phase growth was performed using the growth apparatus shown in FIG.

In the quartz tube 6 in the heating furnace 5, the temperature on the side of the Zn and Te raw materials 7 and 8 is kept constant at 49,000, and the supply amount of the Zn and Te gases is controlled by changing the gas flow rate twice a day. PbMo04 substrate 9 temperature 720°C, main H2 flow rate 200cc'min,
When this was carried out at a carrier gas flow rate of 50 cc'min for Zn and Te, a grown layer with a thickness of several thousand amps to about 100 amps was obtained.
The grown layer was confirmed to be a single crystal thin film by X-ray and electron diffraction, and it was confirmed that it was a PbMo04 crystal (001
) ZnTe (100) was grown on the surface. The optical waveguide test also performed well. [3l Vapor deposition of ZnSe, NTex (0<x<1) on PbMo04
Using the (001) plane of ZnSeo.4 as a substrate, ZnSeo. 5Teo.
5 was used as the evaporation material.

The conditions were almost the same as in Example {1--, and the obtained film was partially single crystallized, and the optical waveguide test showed a slightly larger loss than in {1}. The range value of x is ZnSe,
- The same value as the xTex mixed crystal single crystal production example can be obtained. Z
In addition to nSe and ZnTe, PbW04, SrW04, and Sr
Epitaxial formation on Mo04 and mother W04 was confirmed by X-ray and electron diffraction. The present invention is not limited to the epitaxial method of the above-mentioned embodiments, but can also be applied to liquid phase, gas phase, molecular beam epitaxial, vacuum evaporation methods, and the like.

The optical waveguide device of the present invention uses the characteristics of D-W group compound semiconductors, that is, the optical modulator, optical switch, or photoconductivity shown in FIGS. 3 and 4 that uses the generally well-known electro-optic effect. A photodetector such as that shown in FIGS. 5 and 6 can be constructed.

In Figures 3 and 4, 9 is an AB04 type single crystal substrate, 10
A low group semiconductor single crystal thin film grown on a substrate 9;
Optical waveguides 13, 14 and 15 formed by diffusing impurities into this thin film are electrodes 11 and 12, and this electrode 14
A voltage is applied from a power supply 16 to the optical modulator shown in FIGS. 3 and 4, and the thin films 11 and 12 form a directional optical coupler.

That is, the light 17 incident on the semi-waveguide 11 is modulated by the voltage applied to the electrodes and output from the waveguide. 6th, 6th
In the figure, numerals 9, 10, and 11 are the same as in FIG. 3, and the thin film 11 and electrodes 20 and 21 constitute a Schottky barrier photodiode section.

22 and 23 are lead wires.

This device detects light passing through the thin film 11 using the photodiode section. As described above, the present invention enables the creation of an optical waveguide device for optical waveguide by forming a thin film of a rho group compound semiconductor on an AB04 type tetragonal crystal insulator substrate. By this process, a thin film single crystal with few defects and good crystallinity can be produced, thereby making possible a good thin film optical waveguide device.

In other words, the high electro-optic effect of D-W group crystals makes it possible to fabricate optical modulators and optical switches, as well as Schottky barrier photodetectors and heterojunction photodiodes on the same substrate, making it possible for optical communication. The present invention provides a device useful as a signal processing component for a computer.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the structure of a prism optical coupler for optical waveguide experiments.
FIG. 2 is a schematic configuration diagram of a vapor phase growth apparatus used in an embodiment of the present invention, FIG. 3 is a plan view of an optical modulator to which the present invention is applied, and FIG. 4 is a line m-m' in FIG. 5 is a sectional view of a main part of a photodetector to which the present invention is applied, and FIG. 6 is a sectional view taken along the line V-V' in FIG. 9...AB04 type single crystal substrate, 1 0, 1 1
...Rhocho group compound semiconductor single crystal thin film. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1 ABO_4 type (A: Pb, Ca, Sr, B
A group II-VI cubic compound having a larger optical refractive index than the substrate is placed on a tetragonal oxide substrate (one selected from the group a, B is one selected from the group of Mo and W). An optical waveguide device characterized in that a semiconductor single crystal thin film is formed and an optical waveguide is formed in a predetermined portion of this thin film. 2. The optical waveguide device according to claim 1, wherein the {100} plane of the compound semiconductor is epitaxially grown on the (001) plane of the ABO_4 type crystal. 3 The above compound semiconductor is ZnSe, ZnTe, ZnSe
_1_-_xTe_x (0<x<1), the optical waveguide device according to claim 1, characterized in that it is made of ZnS.