JPS61226729A - Optical element and its production - Google Patents

Abstract

PURPOSE:To improve an extinction ratio, a low operating voltage and a high speed modulating characteristics of the titled element by providing a transparent electrode on a plane meeting at a right angle to a direction of a laminated layer, and by substantially coinciding a resonance wavelength of Fabry-Perot resonator with an optical wavelength which shows the max. optical absorption amount on the prescribed impressed voltage value. CONSTITUTION:An N-type GaAlAs film 13 is formed on a substrate made of N-type GaAs, and a super lattice layer 16 and a P-type GaAlAs film 19 are laminated on the film 13 in order, and then removes the N-type GaAs substrate, thereby controlling a thickness of the N-type GaAlAs film 13. The thickness of the N-type GaAlAs film 13 is reduced to control the thickness of the film so as to approach to the max. optical absorption value. The transparent electrode 20 made of a Cr film and an Au film are formed on the P-type GaAlAs film 19, and the electrode 22 made of the Cr film and the Au film are coated on a part of the electrode 20. The transparent electrode 21 made of the Au film is formed on the N-type GaAlAs film 13. The Au-Ge-Ni-alloy film is coated on a part of the electrode 21, and is heated to stabilize the alloy, thereby obtaining the electrode 23. Therefore, the high speed optical modulating element having a high extinction ratio is obtd.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an optical element that uses a semiconductor multilayer thin film crystal for optical modulation or optical bi-constant operation, and particularly relates to a structure with excellent operating characteristics and a method for manufacturing the same. .

[Background of the invention]

When an electric field is applied to a GaAs/GaAIA+ superlattice multilayer film, the light absorption spectrum of the film changes due to the action of excitons in the film. In other words, the wavelength of light that passes through the film changes. The modulation method is as described by T. Wood et al.
"Fast optical modulation using GaAlAs quantum wells" (Uploaded Physics Letters Vol. 44).

January 1984, pp. 16-18) (T, Woo
d et al.

“H4gh-speed optical module
ation with GaAs/GaAlAs qu
antuae walls in a p-1-nd
iodestructure” (Appl, ph
ys, Lett, VOl, 44. Jan.

1984, ρp16-18)), its structure is shown in FIG. 1, and the experimental results are shown in FIG. It can be seen from FIG. 2 that the amount of light absorbed around 859 nm changes when the applied voltage is ○V and when it is 8V. However, the amount of change in the amount of light absorption is about twice as much, making it difficult to put it into practical use in optical communication technology.

[Purpose of the invention]

The purpose of the present invention is to improve practical performance, especially extinction ratio.

An object of the present invention is to provide an optical semiconductor device with a light modulation function having low operating voltage and high-speed modulation characteristics, and a method for manufacturing the same.

[Summary of the Invention] The present invention will be explained with reference to FIG. 3.The gist of the present invention is to improve the effect of exciton upon voltage application of the superlattice multilayer film 40 and its function as a Fabry-Perot resonator more effectively. In order to achieve this, a transparent electrode 20 is provided on the surface of the superlattice multilayer film 40, and the wavelength and Fabry-Perot resonance are determined at which the amount of light absorbed by the film is maximized when a predetermined voltage is applied to the multilayer film. The aim is to substantially match the peak wavelengths of the instruments.

The transparent electrode is provided to efficiently apply an electric field as uniform as possible to the multilayer film, but depending on the material of the transparent electrode, it can also have the effect of improving the light reflection rate and improving the characteristics of the Fabry-Perot resonator.

In addition, the inventor noticed that the wavelength at which the amount of light absorption of a multilayer film is maximum does not necessarily match the peak wavelength of a Fabry-Perot resonator, and by matching this, practical characteristics can be achieved. It has been found that an optical modulator having the following properties can be obtained. The present inventor also invented a method of adjusting the applied voltage as a method of matching these wavelengths, and also adjusted the film thickness of the multilayer film, particularly the film thickness of the n-type GaAs layer 3 and/or the P-type GaAlAs layer 9. It has been found that matching can be easily achieved by doing this. The easiest way to adjust the film thickness is to form the multilayer film 30, then add the n-type GaAs layer 3 and/or
Alternatively, the p-type GaAlAs layer 9 may be gradually removed to reduce the film thickness. Therefore, as shown in FIG. 4, the multilayer film absorbs light of a predetermined wavelength, and the n-type GaAs layer 3 and/or the p-type GaAlAs layer 9 are gradually removed until the amount of absorbed light reaches a value close to the maximum. do it.

1. The wavelength at which the multilayer film has the maximum light absorption rate and the peak wavelength of the Fabry-Perot cavity do not necessarily have to match perfectly, and the extinction ratio (different applied voltages) of the optical modulator does not necessarily have to match perfectly. Needless to say, it is only necessary that the ratio of the amount of absorbed light in

In the present invention, an extremely high-speed optical modulation element is possible by using GaAs, InP, or the like, which have high carrier mobility, as the semiconductor material. Also, an excellent Fabry
Since a Perot resonator is constructed, a highly reliable optical bistable device is possible.

It goes without saying that these optical elements can be used to perform high-speed optical processing such as two-dimensional image processing and parallel logic processing.

[Embodiments of the invention]

The present invention will be explained in detail below.

Example 1 This will be explained using FIGS. 3 to 8.

First, the manufacturing process of the device will be explained using FIG.

An n-type GaAlAs film 13 with a thickness of 2 μm is formed on an n-type GaAs substrate, and a superlattice layer (II thickness of 8O
16 was formed by the molecular beam epitaxial method, in which 50 layers each of the GaAs film A and the GaAlAs film having a film thickness of 12 OA were laminated alternately. Next, p-type GaAlA is applied on top of it.
After forming the S film 19 to a thickness of 2 μm, the n-type GaAs substrate was removed by mechanochemical and dry etching using CCI, F, and gas. Next, the thickness of the n-type GaAlAs film 13 was adjusted by dry etching using CCQ4 gas. The film thickness was adjusted using the apparatus shown in FIG.

That is, the light source 51, the photoelectric conversion element 52, and the voltmeter 5
3 is used to measure the amount of light absorption of the sample 54, and this amount of light absorption changes periodically as the film thickness of the sample 54 changes.

Therefore, the thickness of the n-type GaAlAs film 13 was reduced by etching to adjust the thickness to a value close to the maximum amount of light absorption.

Next, on the p-type GaAlAs film 19, a Cr film with a thickness of 20A is applied.
A transparent electrode 20 made of an Au film with a thickness of 300 A is formed by vapor deposition, and a C film with a thickness of 300 A is formed on a part of the transparent electrode 20 made of an Au film with a thickness of 300 A.
An electrode 22 made of an r film and an Au film with a thickness of 1 μm was deposited by vapor deposition. Also, an Au film with a thickness of 300 A was formed as a transparent electrode 21 on the n-type GaAlAs film 13.
On a part of it, a film thickness of 1 μm A u -G a -N
i Deposit the alloy film, perform heat treatment to stabilize the alloy,
This was used as the electrode 23.

In addition, device samples were prepared with and without transparent electrodes O and 21, and the characteristics of each device were measured. By adjusting the voltage applied to the electrodes 22 and 23, the amount of light absorbed by the sample can be maximized.

The measurement results will be explained using FIGS. 5 and 6.

Curves 24, 26, 27 and 29 in FIGS. 5 and 6 show the light absorption of the device, and curves 25 and 28 show the light absorption of the device as a Fabry-Perot resonator.

Curves 24 and 29 are for samples in which no transparent electrode is formed, and the applied voltages are 6 V and Ov, respectively. Therefore, the extinction ratio (denoted as data ■) as a light modulation element is the ratio of the light absorption amount at point A of curve 24 and point B of curve 27. The extinction ratio (denoted as data ■) is the ratio of the light absorption amount at point 0 of curve 26 and point D of curve 29, which is much better than data I. Note that the peak of the first curve 28 and the peak of the curve 25 are shifted because the refractive index of the multilayer film changes due to voltage application.

Example 2 - An element having a known structure shown in FIG. 1 was manufactured by applying the present invention.

First, a film with a thickness of 30 mm was formed as a transparent electrode on an n-type InP substrate 1.
A 0A Au film is deposited, a buffer layer 2 of n-InGaAs with a thickness of 0.5 μm is formed on it, an n-type InP layer 3 with a thickness of 1 μm, and an n-type 1n layer with a film thickness Q of 3 pm are formed.
A superlattice buffer layer 4 made of P and InGaAs and a superlattice buffer layer 5 made of InP and InGaAs with a film thickness of 0.3 μm were formed.

Subsequently, a superlattice layer 6 was formed by alternately laminating 50 layers each of InGaAs with a thickness of 150A and InP with a thickness of 120A, and buffer layers 7 and 8 were formed thereon in the same manner as buffer layers 5 and 4. First, a p-type InP film 9 having a film thickness of approximately 1 μm was provided. At this time, the thickness of the film 9 was adjusted in the same manner as in Example 1. On top of that, Cr1l with a film thickness of 20A is used as a transparent electrode.
ll and an Au film with a thickness of 300 Å was deposited. Next, board 1
The central part of the substrate 1 is selectively removed by etching, and then the substrate 1 is etched.
Example 1: An electrode 11 is placed on a part of the upper part, and a p-type InP film 9 is placed on the upper part of the electrode 11.
The fabrication of the sample was completed in the same manner as above. In this case, as in Example 1, samples were prepared with and without transparent electrodes.

6. Curves 30 and 33 are for the case where there is no transparent electrode.

The extinction ratio (denoted as data ■) is the ratio of the light absorption amount at point E of curve 30 and point F of curve 33.

In addition, the light absorption amount of the sample with a transparent electrode is curve 32 and curve 35, and the extinction ratio (data ■) in this case is data ■
Much better.

Note that modulation of 10 GHz was stably realized using the sample of this example.

In this example, the applied voltage was adjusted so that the amount of light absorbed by the sample was maximized. However, in applications that do not require a large extinction ratio, the applied voltage is not necessarily adjusted so that the amount of light absorbed by the sample is maximized. It goes without saying that there is no need to adjust.

It goes without saying that the measurement of the amount of light absorption of the film shown in FIG. 4 can also be carried out in a device for adjusting the film thickness, such as a dry etching device.

Example 3 An optical device was manufactured using the same process as in Example 1.

However, the thickness of the n-type GaAlAs film was not adjusted.

This sample has a wavelength μ! when the applied voltage is 2.5V. The amount of light absorption for light of n was the minimum and maximum at 8.5V.

〔Effect of the invention〕

According to the present invention, it is possible to realize a high-speed optical modulation element with a large extinction ratio, so that it is possible to improve the performance of light wave technology such as optical communication and optical disks.

Furthermore, the present invention, which suggests the possibility of a practical optical bivalent device, has the effect of becoming a fundamental technology for future pure optical computers.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining the prior art, and 3.
4 is a diagram showing a method of adjusting the film thickness, and FIGS. 5, 6, 7, and 8 are diagrams showing characteristics of samples of Examples 1 and 2. DESCRIPTION OF SYMBOLS 1... Substrate (n-type InP base etc.), 2... Buffer layer, 3... N-type InP film, 4, 8... N-type superlattice buffer layer, 5, 7... Superlattice Buffer layer, 6... superlattice layer. 9-p-type InPaM, 10, 11, 22, 23-electrodes,
13- n-type GaAlAs1i, l 6- superlattice layer,
19''' p-type Ga/Ag film, 20.21''・Transparent electrode, 24° 26.29.30, 33.32.35...Curve showing the light transmittance of the element, 25.28, 31.34・・・
・Curve showing the Fabry-Perot resonance of the element, 40...
- Superlattice multilayer film, 51... Light source, 52... Photoelectric conversion element, 53... Voltmeter, 54... Sample.

Claims (1)

[Claims] 1. A multilayer structure that constitutes a Fabry-Perot resonator and has at least one pair of electrodes, and the wavelength of light at which the amount of light absorption reaches a maximum value changes depending on the voltage applied to the electrodes. In an optical element having a film structure, the multilayer film has a transparent electrode on a surface perpendicular to the direction in which the multilayer films are laminated, and a certain applied voltage value (
The wavelength of light at which the amount of light absorption of the multilayer film is at its maximum value when the amount of light absorbed (including zero) is substantially the same as the resonant wavelength (including harmonics) of the multilayer film as a Fabry-Perot resonator. An optical element characterized in that it is configured as follows. 2. A method for manufacturing an optical device that includes a step of configuring a multilayer film that forms a Fabry-Perot resonator and whose wavelength distribution of light absorption changes depending on the applied voltage value, in which a transparent electrode is formed on the multilayer film. process, and the wavelength of light at which the amount of light absorption of the multilayer film reaches its maximum value at a certain applied voltage value (including zero), and the resonant wavelength (including harmonics) of the multilayer film as a Fabry-Perot resonator. 1. A method for manufacturing an optical device, comprising the step of adjusting the thickness of the multilayer film so that the thicknesses of the multilayer film are substantially the same.