JPH04331799A - Production of zinc cadmium sulfide mixed crystal - Google Patents

Abstract

PURPOSE:To provide a method of producing thin film of zinc cadmium sulfide mixed crystal, stably controlling intensity of molecular beam, not exerting bad influence on regulation of conduction type, having no admixture of impurities, having excellent adsorption of molecular beam free from reduction in growth rate. CONSTITUTION:A substance obtained by blending a hydrogen sulfide gas 18a1 with dimethyl sulfur gas 18a2 and cracking is used as a sulfur molecular beam 18e, substances heated and evaporated from a crucible 16a and a crucible 17a are used as a cadmium molecular beam 16c and a zinc molecular beam 17c and the surface of a substrate 14 is irradiated with these molecular beams to grow a thin film of zinc cadmium sulfide mixed crystal on the substrate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cadmium zinc sulfide mixed crystal thin film. In particular, the present invention relates to a method for producing a cadmium-zinc sulfide mixed crystal thin film, which is a semiconductor thin film material that can be usefully used in light-emitting devices such as light-emitting diodes, and exhibits particularly good properties as a material for blue light-emitting devices. It is.

0002

[Prior Art] As a method for producing a cadmium zinc sulfide mixed crystal thin film using the molecular beam epitaxy (MBE) method,
Conventionally, the following three methods are known. Below, Figures 3 to 5
A method of manufacturing a conventional cadmium zinc sulfide mixed crystal thin film by molecular beam epitaxy (MBE) will be described with reference to .

3 to 5 show a molecular beam epitaxial apparatus (hereinafter abbreviated as MBE apparatus) in a conventional MBE method.
FIG. Conventional example 1 is M shown in FIG.
Zinc molecular beams 36c, cadmium molecular beams 37c, obtained by heating and evaporating zinc 36a loaded in a crucible, cadmium 37a loaded in the crucible, and sulfur 38a loaded in the crucible in a vacuum container 31 using a BE device, Sulfur molecular beam 3
This is a method of irradiating the substrate surface with 8c.

Note that 32 is an ultra-high pressure vacuum evacuation device. (In other figures, including this figure, the position of the ultra-high pressure vacuum evacuation device is only shown in the figure, and the details are omitted.) Also, 36b, 37b, and 38b are shutters, and 33 is A substrate holder, 34 is a substrate, and 35 is a cadmium zinc sulfide mixed crystal thin film grown on the substrate. Conventional example 2
Using the MBE apparatus shown in FIG. 4, organic zinc 46a vapor, organic cadmium 47a vapor, and hydrogen sulfide gas 48a were
separate gas cracking cells 46c, 47c,
Zinc molecular beam 46e obtained by thermal decomposition in 48c,
This is a method of irradiating the substrate surface with a cadmium molecular beam 47e and a sulfur molecular beam 48e.

In addition, 41 is a vacuum container, 42 is an ultra-high vacuum pumping device, 43 is a substrate holder, 44 is a substrate, 45 is a cadmium sulfide zinc mixed crystal thin film, 46b, 47b, and 48b are gas flow rate regulators, 46d, 47d , 48d indicates a shutter. Conventional Example 3 uses the MBE apparatus shown in FIG. 5 to heat and evaporate zinc 56a loaded in a crucible and cadmium 57a loaded in a crucible to generate zinc molecular beams 56c and cadmium molecular beams 57c, and cadmium molecular beams 57c in a cylinder. Hydrogen sulfide gas 58a
is supplied to the gas cracking cell 58c while controlling the flow rate with the gas flow rate regulator 58b, and is thermally decomposed in the gas cracking cell 58c to obtain the sulfur molecular beam 58e.
This method involves irradiating the surface of the substrate with

In addition, 51 is a vacuum container, 52 is an ultra-high vacuum evacuation device, 53 is a substrate holder, 54 is a substrate, 55 is a cadmium-zinc sulfide mixed crystal thin film grown on the substrate, 56b, 57
b, 58d indicates a shutter.

[0007]

[Problems to be Solved by the Invention] However, the conventional methods described above have the following problems. In the case of the ordinary MBE method of Conventional Example 1, the vapor pressure of sulfur is very high, so the practical molecular beam intensity (1 × 10-6 To
rr), the temperature of the crucible must be controlled at a low temperature of 100°C or less. Typically, M.B.E.
The device's crucible is designed to generate molecular beams by heating at high temperatures, and the crucible's large heat capacity makes temperature control extremely difficult, leading to problems with unstable molecular beam intensity.

In the case of the MBE method using organic metals in Conventional Example 2, halides are mixed as impurities in the manufacturing process of the organic metal raw materials, and halogens are mixed into the film as donors, making it difficult to control the conductivity type. There was a problem that it became difficult to remove. In the case of Conventional Example 3, in order to overcome the problems of Conventional Examples 1 and 2, hydrogen sulfide and metal vapor were used as raw materials to stabilize the molecular beam intensity of sulfur and maintain high raw material purity. When hydrogen sulfide gas is cracked, a thermal decomposition reaction as shown in (Chemical formula 1) occurs and a large amount of hydrogen is generated.

[0009]

[Chemical formula 1]

[0010] This hydrogen adsorbs to the surface of the grown film to form a hydrogenated film, which inhibits the adsorption of the next incoming molecular beam, resulting in an extremely low growth rate. Ta. In view of these points, the present invention has been developed to provide a sulfurized resin that enables stable control of the intensity of molecular beams, does not contain impurities that adversely affect control of conductivity, has good adsorption of molecular beams, and does not reduce the growth rate. The object of the present invention is to provide a method for producing a cadmium-zinc mixed crystal thin film.

[0011]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a first method for producing a cadmium-zinc sulfide mixed crystal thin film, in which sulfur molecular beams and cadmium are applied to the surface of a substrate in vacuum. In a method of manufacturing a thin film by a molecular beam epitaxy method of irradiating a molecular beam and a zinc molecular beam,
A sulfur molecular beam obtained by thermally decomposing a mixed gas of hydrogen sulfide and dialkyl sulfur is used as the sulfur molecular beam, a molecular beam obtained by heating and vaporizing cadmium is used as the cadmium molecular beam, and a zinc molecular beam is used as the zinc molecular beam. It is characterized by using molecular beams obtained by heating and evaporating.

[0012] Furthermore, in the above structure, it is preferable that the dialkyl sulfur is at least one gas selected from dimethyl sulfur and diethyl sulfur. Further, in the above configuration, it is preferable that the substrate is made of a single crystal of gallium arsenide, gallium phosphorus, or indium phosphorus. Furthermore, in the above configuration, the substrate temperature is 20
The temperature is preferably 0°C or higher and 500°C or lower.

Next, the second method of manufacturing a cadmium-zinc sulfide mixed crystal thin film of the present invention is to form a thin film using a molecular beam epitaxy method in which the surface of a substrate is irradiated with a sulfur molecular beam, a cadmium molecular beam, and a zinc molecular beam in a vacuum. In the method for producing a sulfur molecular beam, a sulfur molecular beam obtained by thermally decomposing hydrogen sulfide is used as the sulfur molecular beam, a molecular beam obtained by heating evaporation of cadmium is used as the cadmium molecular beam, and a zinc molecular beam is used as the zinc molecular beam. The method is characterized in that a molecular beam obtained by heating and evaporating is used, and the surface of the substrate is further irradiated with an unsaturated hydrocarbon molecular beam.

[0014] In the second production method, the unsaturated hydrocarbon is preferably at least one selected from the group consisting of ethylene, propylene, and acetylene.

[0015]

[Operation] The invention of the first manufacturing method includes the above means, namely,
By mixing hydrogen sulfide gas and dialkyl sulfur gas and cracking to obtain a sulfur molecular beam, (Chemical formula 2)
This is based on the action of causing a chemical reaction as shown in Figure 2, suppressing hydrogen generation during thermal decomposition and removing factors that inhibit growth.

[0016]

[Case 2] (R: alkyl group)

[0017] In the first production method, by using a preferable embodiment in which the dialkyl sulfur is at least one gas selected from dimethyl sulfur and diethyl sulfur, the vapor pressure becomes relatively high and a large gas flow rate can be obtained. This makes manufacturing easier.

Further, according to a preferred embodiment of the present invention in which a substrate is made of a single crystal of gallium arsenide, gallium phosphide, or indium phosphide, the lattice constant of these substrates is the same as that of a cadmium zinc sulfide mixture grown on the substrate. Because the lattice constant is similar to that of crystalline thin films, pure single crystals are easy to grow. Further, according to a preferred embodiment of the present invention in which the substrate temperature is set to 200° C. or more and 500° C. or less, the atoms constituting the grown thin film are sufficiently migrated, and each atom is stably arranged at an accurate lattice position. Further, since the defect of atomic vacancies caused by excessive re-evaporation of atoms is suppressed, more perfect crystals can be obtained.

In addition, the invention of the second manufacturing method dissociates multiple bonds between carbon atoms on the surface of the grown film as shown in (Chemical formula 3) by irradiating the unsaturated hydrocarbon molecular beam. This is based on the action of removing hydrogen adsorbed on the surface.

[0020]

[Chemical formula 3] (When ethylene is used as the unsaturated hydrocarbon)

00
[21] Furthermore, in the invention of the second production method, by using a preferable embodiment of using at least one member selected from the group consisting of ethylene, propylene, and acetylene as the unsaturated hydrocarbon, these unsaturated hydrocarbons can be The high vapor pressure makes it easy to control the process, and the impurities that are mixed in do not have a large adverse effect on the properties of the cadmium zinc sulfide mixed crystal thin film.

[0022]

[Examples] The present invention will be explained in detail below with reference to Examples. Example 1 FIG. 1 shows M used in an example of the manufacturing method of the first invention.
FIG. 2 is a schematic diagram showing the structure of a BE device. In the same figure, 16
Metal cadmium and metal zinc are respectively placed in a normal evaporation crucible and evaporated by heating to obtain a cadmium molecular beam 16c and a zinc molecular beam 17c. A gas cracking cell 18c thermally decomposes a mixture of hydrogen sulfide gas introduced from a hydrogen sulfide gas container 18a1 and vaporized dimethyl sulfur 18a2 in the gas cracking cell 18c to obtain sulfur molecular beams 18e.

The 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 made of, for example, molybdenum. Gallium arsenide single crystal, which has a lattice constant close to that of cadmium zinc sulfide, was used as the substrate material. Next, the vacuum container 11 is evacuated to an ultra-high vacuum of about 10 -9 Torr or less by the ultra-vacuum exhaust device 12 . Thereafter, the crucibles 16a and 17a are heated to, for example, about 120° C. and 240° C., so that cadmium molecular beams 16c and zinc molecular beams 17c with appropriate strength (about 1×10 −6 Torr) are obtained. Also, hydrogen sulfide gas 18a1 and dimethyl sulfur gas 1
8a2 are separate gas flow rate regulators 18b1 and 18b, respectively.
After adjusting the flow rate in Step 2, mix and mix to an appropriate strength (approximately 1 x 10
-6 Torr) to obtain the sulfur molecular beam 18e. When the temperature of the gas cracking cell 18c was 400° C. or higher, the hydrogen sulfide/dimethyl sulfur mixed gas could be cracked almost completely.

Next, the substrate 14 is heated to about 600° C. to remove the surface oxide film. Thereafter, the substrate 14 is lowered to a temperature suitable for crystal growth. In this case, the temperature was, for example, 300°C. After this, the shutters 16b, 17b, and 18d are simultaneously opened to perform crystal growth. The cadmium-zinc sulfide mixed crystal thin film 15 formed by the method described above is cracked by mixing hydrogen sulfide and dimethyl sulfur, thereby suppressing the generation of hydrogen and reducing the adhesion coefficient to approximately 1, resulting in a high growth rate. Ta. Here, the adhesion coefficient refers to the ratio of the number of atoms attached and grown on the substrate to the number of atoms supplied as molecular beams.

[0025] It was also clear from hydrogen concentration measurement using a quadrupole mass spectrometer that hydrogen generation was suppressed. Also, the mixing ratio of hydrogen sulfide and dimethyl sulfur is 1:
The cadmium sulfide mixed crystal thin film produced in Example 1 had the best crystallinity. In addition, although dimethyl sulfur was used as the dialkyl sulfur compound in the above-mentioned example, the same effect was obtained even if diethyl sulfur was used. Here, dimethyl sulfur was used as the dialkyl sulfur because dimethyl sulfur has a higher vapor pressure than diethyl sulfur, so a larger gas flow rate can be obtained.

Furthermore, the reason why metals are used as zinc and cadmium raw materials and organic metal raw materials are not used is that organic metals have poorer chemical purity and are more likely to be contaminated with components that have an adverse effect as impurities. In particular, halogen is likely to be mixed in, and if halogen is mixed in, the degree of freedom in controlling the conduction type will be inhibited, which is not preferable. In addition, the substrate temperature during thin film formation is such that sufficient migration of the thin film forming atoms on the substrate surface occurs, each atom is easily stabilized at a precise lattice position, and re-evaporation of atoms does not become excessive, leaving atomic vacancies. 2. Because there is less possibility of forming pores and it is easier to obtain perfect crystals.
A temperature of 00°C or more and 500°C or less was suitable.

Furthermore, substantially the same results were obtained when a substrate made of a single crystal of gallium phosphide or indium phosphorus was used instead of a substrate made of a single crystal of gallium arsenide.

Example 2 FIG. 2 shows an M used in an example of the manufacturing method of the second invention.
FIG. 2 is a schematic diagram showing the structure of a BE device. In the same figure, 26
Metal cadmium and metal zinc are respectively placed in a normal evaporation crucible and evaporated by heating to obtain a cadmium molecular beam 26c and a zinc molecular beam 27c. 2
8c is a gas cracking cell that thermally decomposes hydrogen sulfide gas 28a introduced from a hydrogen sulfide gas container to obtain sulfur molecular beams 28e. Further, 29a is ethylene gas, which is supplied to the surface of the substrate 24 from the gas introduction port 29c.

The actual thin film growth is carried out in the following manner. First, the substrate 24 whose surface has been cleaned is mounted on the substrate holder 23 made of, for example, molybdenum. As the substrate material, we used a single crystal of gallium arsenide, which has a lattice constant close to that of cadmium zinc sulfide. Next, the vacuum container 21 is heated to 10-9 Torr using an ultra-high vacuum evacuation device 22.
Evacuate to an ultra-high vacuum of the following level. Thereafter, the crucibles 26a and 27a are heated to, for example, about 120° C. and 240° C. to obtain cadmium molecular beams 26c and zinc molecular beams 27c with appropriate strength (about 1×10 −6 Torr). The flow rate of hydrogen sulfide is adjusted by a gas flow rate regulator 28b so that a sulfur molecular beam 28e of appropriate strength (approximately 1×10 −6 Torr) is obtained. gas cracking cell 2
If the temperature of 8c was 700°C or higher, hydrogen sulfide gas could be almost completely cracked. The flow rate of ethylene gas 29a as a dehydrogenating agent was controlled by a gas flow rate regulator 29b (eg, 50 sccm in this case), and the substrate was directly irradiated with it as an ethylene molecular beam 29e.

Next, the substrate 24 is heated to about 600° C. to remove the surface oxide film. The substrate is then lowered to a temperature suitable for crystal growth. In this case, the temperature was, for example, 300°C. After that, the shutters 26b, 27b, 28d, and 29d are simultaneously opened to perform crystal growth. The cadmium zinc sulfide mixed crystal thin film 25 formed by the method described above can be grown by supplying ethylene, which is an unsaturated hydrocarbon, to efficiently desorb hydrogen attached to the surface of the grown film. An increase in velocity was observed and the sticking coefficient was approximately 0.5. The higher the flow rate of ethylene gas, the greater the dehydrogenation effect, but if the flow rate is too high, the pressure inside the vacuum vessel 21 will increase, making it impossible to obtain a molecular beam, which is one of the advantages of the MBE method. In this case, it was preferable to set the flow rate to 100 sccm or less, since in-situ observation devices such as a quadrupole mass spectrometer and a reflection high-speed electron diffraction device become unusable.

[0031] Although ethylene was used as the unsaturated hydrocarbon in the above-mentioned examples, similar effects could be obtained by using propylene or acetylene. Furthermore, substantially the same results were obtained when a substrate made of a single crystal of gallium phosphorus or indium phosphorus was used instead of a substrate made of a single crystal of gallium arsenide.

[0032] Also in the second invention, the substrate temperature during thin film formation was preferably 200°C or more and 500°C or less. It should be noted that the dialkyl sulfur used in the present invention has a higher vapor pressure when the alkyl group has a smaller number of carbon atoms.
It is preferable from the viewpoint of reducing the amount of impurities after decomposition, and those in which the number of carbon atoms in the alkyl group is 3 or less, particularly 2 or less are preferable.

[0033] For the same reason, unsaturated hydrocarbons are preferably unsaturated hydrocarbons having 2 to 4 carbon atoms.
In particular, unsaturated hydrocarbons having 2 to 3 carbon atoms are preferred. Also,
The degree of vacuum in the vacuum chamber varies depending on the distance between the molecular beam source and the substrate and the type of molecular beam source used, but the vacuum is such that the distance between the molecular beam source and the substrate is within the mean free path of the molecular beam. It is preferable that the pressure is usually 10 −5 Torr or less,
The higher the vacuum, the more preferable it is.

[0034]

Effects of the Invention In the first manufacturing method, the intensity of the molecular beam can be stably controlled, there is no contamination of impurities that would adversely affect the control of the conductivity type, and hydrogen generation due to gas cracking is prevented. It is possible to provide a method for producing a cadmium zinc sulfide mixed crystal thin film that can suppress the formation of a hydrogen film on the surface, has good molecular beam adsorption, and does not reduce the growth rate.

[0035] Furthermore, by adopting a preferable embodiment in which at least one gas selected from dimethyl sulfur and diethyl sulfur is used as the dialkyl sulfur, the vapor pressure becomes relatively high and a large gas flow rate can be obtained, making the production easier. becomes easier. Further, in a preferred embodiment, a substrate made of a single crystal of gallium arsenide, gallium phosphorus, or indium phosphorus is used as the substrate, making it easier to obtain a pure single crystal.

[0036] Furthermore, by setting the substrate temperature to 200° C. or more and 500° C. or less, the atoms constituting the grown thin film are sufficiently migrated, and each atom is stably arranged at an accurate lattice position. Further, since the defect of atomic vacancies caused by excessive re-evaporation of atoms is suppressed, more perfect crystals can be obtained. Second
In the invention of the manufacturing method, it is possible to stably control the intensity of the molecular beam, there is no contamination of impurities that would adversely affect the control of the conductivity type, and it is possible to desorb hydrogen attached to the surface of the grown film. It is possible to form a cadmium zinc sulfide mixed crystal thin film without inhibiting growth.

[0037] Furthermore, in the invention of the second production method, in a preferred embodiment, at least one selected from the group consisting of ethylene, propylene, and acetylene is used as the unsaturated hydrocarbon. Since the vapor pressure is high, the process can be easily controlled, and the impurities mixed in do not have a large adverse effect on the properties of the produced cadmium zinc sulfide mixed crystal thin film.

As a result of the above, it is possible to grow a high-quality cadmium-zinc sulfide mixed crystal thin film, and in turn, it is possible to provide a method for producing a cadmium zinc sulfide mixed crystal thin film that can be applied to high-efficiency blue light-emitting devices.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of an MBE apparatus for producing a cadmium zinc sulfide mixed crystal thin film in an embodiment of the first invention.

FIG. 2 is a schematic diagram showing the structure of an MBE apparatus for producing a cadmium zinc sulfide mixed crystal thin film in an embodiment of the second invention.

FIG. 3 is a schematic diagram showing the structure of an MBE device used in Conventional Example 1.

FIG. 4 is a schematic diagram showing the structure of an MBE device used in Conventional Example 2.

FIG. 5 is a schematic diagram showing the structure of an MBE device used in Conventional Example 3.

[Explanation of symbols]

11 Vacuum container 12 Ultra-high vacuum evacuation device 13 Substrate holder 14 Substrate 15 Cadmium-zinc sulfide mixed crystal thin film 16a Metal cadmium 16b in crucible Shutter 16c Cadmium molecular beam 17a Metal zinc 17b in crucible Shutter 17c Zinc molecular beam 18a1 Hydrogen sulfide Gas 18b1 Gas flow rate regulator 18a2 Dimethyl sulfur 18b2 Gas flow rate regulator 18c Gas cracking cell 18d Shutter 18e Sulfur molecular beam 21 Vacuum vessel 22 Ultra-high vacuum exhaust device 23 Substrate holder 24 Substrate 25 Cadmium-zinc sulfide mixed crystal thin film 26a Entered the crucible Metal cadmium 26b Shutter 26c Cadmium molecular beam 27a Metal zinc 27b in crucible Shutter 27c Zinc molecular beam 28a Hydrogen sulfide gas 28b Gas flow rate regulator 28c Gas cracking cell 28d Shutter 28e Sulfur molecular beam 29a Ethylene gas 29b Gas flow rate regulator 29c Gas Introduction port 29d Shutter 29e Ethylene molecular beam 31 Vacuum vessel 32 Ultra-high vacuum exhaust device 33 Substrate holder 34 Substrate 35 Cadmium zinc sulfide mixed crystal thin film 36a Metal zinc 36b in crucible Shutter 36c Zinc molecular beam 37a Metal cadmium 37b in crucible Shutter 37c Cadmium molecular beam 38a Sulfur 38b in the crucible Shutter 38c Sulfur molecular beam 41 Vacuum vessel 42 Ultra-high vacuum exhaust device 43 Substrate holder 44 Substrate 45 Cadmium zinc sulfide mixed crystal thin film 46a Organic zinc 46b Gas flow regulator 46c Gas cracking cell 46d Shutter 46e Zinc molecular beam 47a Organic cadmium 47b Gas flow rate regulator 47c Gas cracking cell 47d Shutter 47e Cadmium molecular beam 48a Hydrogen sulfide gas 48b Gas flow rate regulator 48c Gas cracking cell 48d Shutter 48e Sulfur molecular beam 51 Vacuum vessel 52 Ultra-high vacuum Exhaust device 53 Substrate holder 54 Substrate 55 Cadmium zinc sulfide mixed crystal thin film 56a Metal zinc 56b in crucible Shutter 56c Zinc molecular beam 57a Metal cadmium 57b in crucible Shutter 57c Cadmium molecular beam 58a Hydrogen sulfide gas 58b Gas flow rate regulator 58c Gas cracking cell 58d Shutter 58e Sulfur molecular beam

Claims (6)

[Claims] 1. A method for manufacturing a thin film by a molecular beam epitaxy method in which a substrate surface is irradiated with a sulfur molecular beam, a cadmium molecular beam, and a zinc molecular beam in a vacuum, wherein the sulfur molecular beams include hydrogen sulfide and dialkyl sulfur. A sulfur molecular beam obtained by thermally decomposing a mixed gas is used, a molecular beam obtained by heating and evaporating cadmium is used as the cadmium molecular beam, and a molecular beam obtained by heating and evaporating zinc is used as the zinc molecular beam. A method for producing a cadmium zinc sulfide mixed crystal thin film, characterized by: 2. The method for producing a cadmium zinc sulfide mixed crystal thin film according to claim 1, wherein the dialkyl sulfur is at least one gas selected from dimethyl sulfur and diethyl sulfur. 3. The method for producing a cadmium zinc sulfide mixed crystal thin film according to claim 1, wherein the substrate is a single crystal of gallium arsenide, gallium phosphide, or indium phosphide. 4. The method for producing a cadmium zinc sulfide mixed crystal thin film according to claim 1, wherein the substrate temperature is 200° C. or more and 500° C. or less. 5. A method for manufacturing a thin film by a molecular beam epitaxy method in which a substrate surface is irradiated with a sulfur molecular beam, a cadmium molecular beam, and a zinc molecular beam in a vacuum, wherein hydrogen sulfide is thermally decomposed as the sulfur molecular beam. Using a sulfur molecular beam obtained by heating and evaporating cadmium as the cadmium molecular beam, using a molecular beam obtained by heating and evaporating zinc as the zinc molecular beam, A method for producing a cadmium zinc sulfide mixed crystal thin film, which comprises irradiating a substrate surface with a hydrogen molecular beam. 6. The unsaturated hydrocarbon is at least one selected from the group consisting of ethylene, propylene, and acetylene.
The method for producing a cadmium zinc sulfide mixed crystal thin film according to claim 5, wherein the cadmium zinc sulfide mixed crystal thin film is a seed.