JPH04202098A - Method for producing cubic cadmium zinc sulfide mixed crystal thin film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing semiconductor thin film materials used in light emitting devices such as light emitting diodes, and in particular, cubic sulfide which exhibits good properties as a material for blue light emitting devices. The present invention relates to a method for producing a cadmium-zinc mixed crystal thin film.

[Prior Art] As a conventional method for manufacturing a cubic cadmium zinc sulfide mixed crystal thin film, a molecular beam epitaxy apparatus as shown in FIG. A method is known in which a cadmium raw material 26a and a zinc sulfide raw material 27a loaded in a crucible 27 are heated and evaporated to form a cubic cadmium zinc sulfide mixed crystal thin film 25 on the surface of the substrate 24.

[Problem to be solved by the invention] However, in the conventional method as described above, the adhesion coefficient of cadmium sulfide flying onto the substrate surface is low, so cadmium sulfide is desorbed from the state of physical adsorption on the substrate surface, and mixed crystals are formed. It was difficult to form a mixed crystal thin film in a region with a high cadmium composition ratio. Another possibility is to lower the substrate temperature to suppress the desorption of cadmium sulfide, but if the substrate temperature is too low (too low), the physically adsorbed molecules will not have enough energy to migrate, resulting in structural defects. There were problems such as the occurrence of

SUMMARY OF THE INVENTION In order to solve the problems of the prior art, it is an object of the present invention to provide a method for manufacturing a cubic cadmium zinc sulfide mixed crystal thin film that is structurally free from defects.

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing a cubic cadmium zinc sulfide mixed crystal thin film of the present invention includes a method for producing a cubic cadmium zinc sulfide mixed crystal thin film, in which sulfur molecular beams, cadmium molecular beams, and zinc molecules are formed on the surface of a substrate in vacuum. In the method of manufacturing a thin film by irradiating a sulfur molecular beam with a radical sulfur molecular beam obtained by thermally decomposing hydrogen sulfide, the cadmium molecular beam is a radical sulfur molecular beam obtained by thermally decomposing hydrogen sulfide, and the cadmium molecular beam is a radical sulfur molecular beam obtained by thermally evaporating metallic cadmium or an organic cadmium compound. A molecular beam obtained by thermally decomposing a gas is used, and a molecular beam obtained by thermally evaporating metallic zinc or thermally decomposing a gas of an organic zinc compound is used as the zinc molecular beam. do.

In the above configuration, it is preferable to use a single crystal of gallium arsenide, gallium phosphide, or indium phosphide as the substrate.

In addition, in the above configuration, the substrate temperature is set at 200°C or more.
The temperature is preferably 00°C or lower.

[Function] According to the configuration of the present invention, sulfur can be effectively incorporated into the thin film by using a highly reactive radical sulfur molecular beam, and the constituent elements (sulfur, cadmium,
Desorption of cadmium sulfide molecules can be suppressed by individually supplying cadmium sulfide (zinc). As a result, a highly efficient blue light emitting element with few structural defects can be obtained.

By using radicals, it is possible to reduce the pressure during growth, which reduces the incorporation of impurities, and because the substrate temperature during growth can be kept in a temperature energy range sufficient for surface molecules to migrate. This has the effect of reducing the occurrence of structural defects.

In addition, as described above, gallium arsenide, gallium phosphorus,
According to the preferred configuration of the present invention in which a single crystal of indium phosphorous is used, it is possible to have a lattice constant close to that possible for cubic cadmium zinc sulfide, and furthermore, it is possible to reduce structural defects. can.

Further, according to the above-described preferred configuration of the present invention in which the substrate temperature is set to 200° C. or more and 500° C. or less, it is possible to form a thin film favorably.

"Example code" EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples.

FIG. 1 is a schematic diagram showing the structure of a molecular beam epitaxy apparatus used in an embodiment of the manufacturing method of the present invention. In the same figure, 16 and 17 are ordinary evaporation crucibles, and metal cadmium 16a and metal zinc 17 are raw materials, respectively.
A is loaded and heated to evaporate to form a cadmium molecular beam 1.
6c and zinc molecular beam 17c are obtained.

Further, 18 is a gas decomposition cell in which the gas introduced from the hydrogen sulfide gas container 18a is converted into radicals by a radical generator using thermal energy, resulting in radical sulfur molecular beams 18.
get c.

Here, the reason why hydrogen sulfide gas is used as the raw material for the sulfur molecular beam is that elemental sulfur (solid) has a fairly high vapor pressure even at room temperature, so the heating and degassing treatment of the vacuum vessel 11 is essential for obtaining a high vacuum. This is because it evaporates during the process, making it impractical.

Actual thin film growth is performed in the following steps. First, the substrate 14 whose surface has been cleaned is mounted on the substrate holder 13. As the substrate material, single crystals such as gallium arsenide, gallium phosphide, and indium phosphide, which have lattice constants close to those of cubic cadmium zinc sulfide, have been preferred. Next, the vacuum container 11 is evacuated to about 10'Tott or less. Thereafter, the crucibles 16 and 17 are heated to, for example, 400°C.
The cadmium molecular beam 16c and the zinc molecular beam 17c are heated to a certain degree so as to obtain a cadmium molecular beam 16c and a zinc molecular beam 17c of appropriate strength.

In addition, the flow rate control valve 18d is opened to allow hydrogen sulfide gas to flow into the radical generator, and the radical sulfur molecular beam 18 has an appropriate strength.
so that c can be obtained. The temperature of the radical generator is
At 700°C or higher, hydrogen sulfide gas could be almost completely radicalized.

Next, the substrate 14 is heated to about 600° C. to further clean the surface. The substrate is then lowered to a temperature suitable for crystal growth.

In this case, the temperature is, for example, 300°C.

After this, the shutters 16b, 17b, and 18b are opened simultaneously to perform crystal growth.

In the cubic cadmium zinc sulfide mixed crystal thin film formed by the method described above, the reactivity of sulfur molecular beams was increased due to the use of radicals, and the rate of sulfur incorporation was increased. As a result, the amount of hydrogen sulfide gas to be supplied was small, which suppressed the amount of impurities incorporated into the film and reduced the carrier density of the undoped sample. In addition, since the desorption of cadmium sulfide molecules from the substrate surface is suppressed, the substrate temperature during growth can be raised to allow crystal growth in a temperature range where sufficient migration of atoms on the substrate surface occurs, resulting in lattice defects. As for the optical properties, the emission from deep levels decreased and the half-value width of the emission peak became narrower.

In the above example, metal cadmium was used as the raw material for the cadmium molecular beam, and metal zinc was used as the raw material for the zinc molecular beam. Similar effects were obtained using compound gas.

Also, the substrate temperature during thin film formation is 200'C or more and 50'C.
C or less was suitable. At temperatures below 200'C, the migration of atoms on the substrate surface is not sufficient, so each atom is not stabilized at a precise lattice position, and at temperatures above 500'C, there is excessive re-evaporation of atoms, creating atomic vacancies. Therefore, perfect crystals cannot be obtained in either case.

As explained above, in this example, the elements constituting the cadmium-zinc sulfide mixed crystal (sulfur, cadmium, zinc) are individually supplied, and a highly reactive radical sulfur molecular beam is used as the sulfur source. By improving the incorporation rate of cadmium sulfide and suppressing the desorption of cadmium sulfide, it is possible to form a cubic cadmium zinc sulfide mixed crystal thin film with excellent quality in terms of crystal purity and structure. the result,
This will lead to the realization of highly efficient blue light emitting devices, and its practical effects will be significant.

[Effects of the Invention] As explained above, according to the invention in which a cubic cadmium zinc sulfide mixed crystal thin film is obtained by irradiating a substrate surface with a radical sulfur molecular beam, a cadmium molecular beam, and a zinc molecular beam in a vacuum, By improving the sulfur incorporation rate and suppressing the desorption of cadmium sulfide, it is possible to form a cubic cadmium zinc sulfide mixed crystal thin film with excellent quality in terms of crystal purity and structure.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of a molecular beam epitaxy apparatus for producing a cubic cadmium zinc sulfide mixed crystal thin film in the first embodiment of the present invention, and FIG. 2 is a schematic diagram showing the structure of a molecular beam epitaxy apparatus used in a conventional example. It is a schematic diagram showing a structure. 11... Vacuum container, 12... Ultra-high vacuum exhaust device, 1
3... Substrate holder, 14... Substrate, 15... Cadmium zinc sulfide mixed crystal thin film, 16... Crucible for cadmium, 16a... Metal cadmium, 16b... Shutter, 16c... Cadmium Molecular beam, 17... Zinc crucible, 17a... Metal zinc, 17b... Shutter, 17c... Zinc molecular beam, 18... Radical generator, 1-8a... Hydrogen sulfide gas container , 18b・
...Shutter, 18C...Radical sulfur molecular beam, 1
8d... Gas flow rate control valve, 21... Vacuum container, 22
...Ultra-high vacuum exhaust system, 23...Substrate holder, 2
4... Substrate, 25... Cadmium zinc sulfide mixed crystal thin film, 26... Crucible for cadmium sulfide, 26a... Cadmium sulfide, 26b... Shutter, 26c...
Cadmium sulfide molecular beam, 27... crucible for zinc sulfide,
27a...Zinc sulfide, 27b...Shutter, 27
c...Zinc sulfide molecular beam. Name of agent: Patent attorney Hiroyuki Ikeuchi Haka 1 person 11...
Vacuum container 12...ultra-high vacuum exhaust device

Claims (3)

[Claims] (1) In a method of manufacturing a thin film by irradiating a substrate surface with a sulfur molecular beam, a cadmium molecular beam, and a zinc molecular beam in a vacuum, the sulfur molecular beam is a radical sulfur molecule obtained by thermally decomposing hydrogen sulfide. using a molecular beam obtained by heating and evaporating metal cadmium or thermally decomposing a gas of an organic cadmium compound as the cadmium molecular beam,
A method for producing a cubic cadmium zinc sulfide mixed crystal thin film, characterized in that the zinc molecular beam is a molecular beam obtained by heating and evaporating metallic zinc or thermally decomposing a gas of an organic zinc compound. (2) The method for producing a cubic cadmium zinc sulfide mixed crystal thin film according to claim 1, wherein a single crystal of gallium arsenide, gallium phosphorus, or indium phosphorus is used as the substrate. (3) The method for producing a cubic cadmium zinc sulfide mixed crystal thin film according to claim 1 or 2, wherein the substrate temperature is 200°C or more and 500°C or less.