JPH05109621A - Method for growing gallium nitride thin film - Google Patents

Abstract

PURPOSE:To obtain a GaN semiconductor thin film which is suitable for optical element at ultraviolet to blue color regions. CONSTITUTION:When producing a GaN semiconductor thin film by the gas source MBE method, a thin film with an improved semiconductor property is obtained by supplying a raw material to a substrate 7 intermittently or alternately or providing a time where no raw materials are supplied, thus enabling flattening property and crystallinity to be improved and obtaining a semiconductor thin film which is optimum for a light-emitting element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride-based thin film which can be used particularly for displays, ultraviolet to blue light emitting diodes, laser diodes, etc., which are optimal for optical communication.

[0002]

2. Description of the Related Art Semiconductor devices, particularly visible light emitting diodes (LEDs), are used as display devices in a wide range of fields, but ultraviolet to blue light emitting diodes and laser diodes have not been put into practical use. Development is urgently needed for displays that require three primary colors. Ultraviolet to blue light emitting diodes and laser diodes using ZnSe, ZnS, GaN, SiC or the like have been reported.

Gallium nitride (GaN) is often
The MOCVD method using trimethylgallium or triethylgallium as a raw material or the VPE method is used to continuously supply the raw material onto the sapphire substrate to form a film [J.
ournal of Applied Physics, 56 P.2367-2368 (198
Four)]. In these methods, it is necessary to raise the reaction temperature, which makes production difficult, and since nitrogen is insufficient, the carrier density becomes extremely large, and good semiconductor characteristics cannot be obtained. Further, since it is necessary to use a raw material containing carbon and the pressure during film formation is relatively high, carbon is often incorporated as an impurity in the thin film, and thus GaN having low characteristics is used.
Only thin films can be obtained.

Further, since the GaN-based thin film does not have a GaN single crystal substrate, there is a problem that the thin film growth must be performed by the heteroepitaxy method. for that reason,
Conventionally, a sapphire substrate is used and G is grown thereon.
Ga used as a light-emitting element by increasing the thickness of the aN-based thin film or providing an AlN buffer layer
An N-based thin film was obtained. However, the GaN-based thin film obtained by these methods is still insufficient as a light-emitting element, such as luminescence observed due to impurities and crystal defects, and it is necessary to increase the thickness of the GaN-based thin film. When it is used as a light emitting element, there are drawbacks such as a decrease in light extraction efficiency.

However, it is described in Japanese Patent Application No. 3-179407 that a thin film having good characteristics can be produced by forming a film using the gas source MBE method. In the gas source MBE method, since the film formation is performed in a high vacuum, the mixing of impurities can be suppressed, and since the film formation can be performed at a low temperature, a favorable thin film with few nitrogen vacancies can be formed.

GaN using the conventional gas source MBE method
In the growth method of the system-based thin film, since the raw material is continuously supplied onto the substrate, in order to perform two-dimensional crystal growth, it is necessary to highly control the raw material supply rate to the substrate and the growth temperature. However, it was not sufficient to produce a flat thin film with few defects and high crystallinity with good reproducibility.

[0007]

In order to produce a GaN-based thin film having excellent characteristics as a semiconductor thin film for a light emitting device, the film surface is flat, there are few defects, and the luminescence characteristics are good, and therefore the crystallinity is excellent. Although it is necessary to produce thin films with good reproducibility, the present situation is still unsatisfactory. The present invention solves this problem and can be used for a light emitting device in the visible to ultraviolet region.
It is intended to provide an N-based thin film.

[0008]

The inventors of the present invention have found that a gallium nitride-based thin film grown by intermittently supplying a raw material onto a substrate using a gas source MBE method emits light in the visible to ultraviolet region. As a result of discovering that it has excellent properties as a material and further earnestly researching it, the present invention has been completed.

According to the present invention, the group III element and the group V element are alternately supplied onto the substrate by using the gas source MBE method, or the group III element is intermittently supplied while continuously supplying the group V element. The method is a method for growing a gallium nitride-based thin film, which comprises supplying the material or providing a time during which the material is not supplied to the substrate during the thin film growth. As the Group III element, a gallium metal, alloy or organometallic compound is mainly used, and if necessary, at least one metal, alloy or organometallic compound of In, Al and B can be used together. Examples of alloys include Ga.
Examples include In alloys, In.Al alloys, Ga.Al alloys, and the like. Examples of organometallic compounds include trimethylgallium, triethylgallium, trimethylindium, and trimethylaluminum. Here, the metal and the alloy are supplied from the evaporation crucible, and the organic metal is supplied through the gas cell.

As the group V element, nitrogen is mainly used, and if necessary, at least one of P, As, and Sb can be used in combination. As the nitrogen source, ammonia, hydrazine, trimethylamine, triethylamine, or a mixed gas thereof can be used, and an inert gas may be mixed if necessary. In addition, nitrogen plasma,
Nitrogen trifluoride, a mixed gas of nitrogen trifluoride and nitrogen or helium can be used.

The supply amount of the group V element needs to be larger than the supply amount of the group III element on the surface of the substrate, and when the supply amount of the group V element is smaller than the supply amount of the group III element, a GaN-based thin film is formed. It becomes impossible to obtain a good GaN-based thin film because the escape of nitrogen from the substrate becomes large. Therefore, it is preferable that the beam intensity of the group V element on the surface of the substrate is equal to or higher than the beam intensity of the group III element.

A gas cell may be used as a method for supplying the group V element, and a tube of boron nitride, alumina, quartz, stainless steel or the like is installed in the thin film growth apparatus with the opening facing the substrate surface, and a valve or flow rate is used. By connecting a control device and a pressure control device, the supply amount can be controlled and the supply can be started and stopped. It is also preferable to use a cracking gas cell because the nitrogen source is decomposed and active nitrogen is efficiently supplied to the substrate surface. The cracking gas cell is a cell that heats a nitrogen source in the presence of a catalyst to efficiently generate active nitrogen, and the catalyst is a fibrous or porous ceramic such as alumina, silica, boron nitride, or silicon carbide. It is preferable that the surface area be increased so as to increase the surface area. It is necessary to change the cracking temperature depending on the type of catalyst and the supply amount of nitrogen source.
It is preferable to set in the range of 0 to 600 ° C. P, As and Sb can be supplied as a solid source or a gas source.

The substrate used in the present invention is S
i, Al ₂ O ₃ , ZnO, MgO, SiC, or G
III-V group compounds such as aAs and InAs, ZnSe
A single crystal substrate such as a II-VI group compound or the like, a glass substrate such as quartz glass, MESA glass, or the like is used. Further, as a buffer layer between the substrate and the GaN-based thin film, an amorphous substance such as AlN, GaN, Si, or SiC is used.
Alternatively, as a single crystal substance, for example, AlN, ZnO, S
iC etc. can be provided. Among them, it is preferable to use an R-plane substrate for sapphire (Al ₂ O ₃ ), and its off angle is preferably 0.8 degrees or less in order to obtain a highly oriented GaN thin film. Furthermore, it is also preferable to use a surface obtained by rotating the sapphire R surface by 9.2 degrees about the R surface projection of the sapphire c axis. The substrate is heated in the range of 200 to 900 ° C. by the substrate heating device.

The GaN-based thin film in the present invention means, for example, Ga _1-x Al _x N, Ga _1-x In _x N, G in addition to GaN.
a _1-x B _x N is that of mixed crystal compound thin film mainly composed of GaN, such as. Further, when a GaN-based thin film is manufactured, impurities are doped to control carrier density, p-type, i
Type or n-type control can also be performed. Examples of impurities to be doped are Mg, Zn, Be, Sb, Si,
Ge, C, Sn, Hg, As, P and the like. The type of carrier and the carrier density can be changed by changing the type, doping amount and doping position of these dopants.

In the method for growing a gallium nitride-based thin film of the present invention, the method for supplying and stopping the group III element and the group V element on the substrate is performed by opening and closing the shutter of the crucible in the case of a solid source. The source can be controlled by opening and closing the valve of the gas cell. For example, a solid source is used as the group III element and a gas source is used as the group V element, and I
When the group II element and the group V element are alternately supplied, II
Open the shutter of the crucible for group I element and set it from 0.1 to 10
After the group III element for the atomic layer is supplied, the shutter is closed and at the same time the group V element is changed from 1 × 10 ¹⁶ to 1 from the gas cell.
It is supplied with a beam intensity of × 10 ²⁰ / cm ² · sec.
The supply of the group V element is stopped after 1 to 100 seconds, and at the same time, the shutter of the crucible for the group III element is opened to supply the group III element, and the same process is repeated to obtain a thin film having a required thickness. Here, the growth method of supplying just one atomic layer by opening and closing the shutter once for the Group III element is more preferable in order to form a thin film having good crystallinity.

As a powerful means for controlling the element supply amount on the atomic layer order, there is a high speed electron diffraction method. By observing the change in the brightness of the diffraction spot while forming the film, vibration corresponding to the stacking of atomic layers can be obtained. Therefore,
By synchronizing the opening and closing of the shutter and the valve with the vibration of electron beam diffraction, the element supply amount can be controlled on the atomic layer order.

When the group III element is intermittently supplied while continuously supplying the group V element onto the substrate, the group V element is supplied from the gas cell at 1 × 10 ¹⁶ to 1 × 10 ²⁰ / cm ² · sec.
Open the shutter of the crucible for group III element while continuously supplying with the beam intensity of 0.1 to 1
After supplying 0 atomic layer, close the shutter. 0.1 to 100 seconds after the shutter is closed, the shutter is opened again and the same process is repeated to obtain a thin film having a required thickness.
Here, the growth method of supplying just one atomic layer by opening and closing the shutter once for the Group III element is more preferable in order to form a thin film having good crystallinity.

Furthermore, by providing a time during which neither the group III element nor the group V element is supplied during the film formation, each element is allowed to diffuse on the surface, resulting in a flatter and more defective surface. It is possible to form a thin film having a small amount and high crystallinity. Here, the time when neither group III element nor group V element is supplied is 0.1 to 1 continuously.
It can be set to 00 seconds and can be provided multiple times during one film formation.

Method 1 for growing a gallium nitride thin film of the present invention
Here is an example. A gas source MBE equipped with a vaporizing crucible containing Ga metal in a vacuum container and a cracking gas cell filled with alumina fibers was used as an apparatus. A sapphire R surface was used as the substrate and heated to 750 ° C. The Ga crucible was heated to 1050 ° C. The cracking cell is heated to 400 ° C to add 1x ammonia.
It was supplied with a beam intensity of 10 ¹⁸ / cm ² · sec and sprayed onto a sapphire substrate. In this state, the shutter of the crucible was opened, Ga was supplied for one atomic layer, and then the shutter was closed.
After 20 seconds, the shutter was opened again to supply Ga for one atomic layer. This was repeated to obtain a 0.8 μm gallium nitride thin film.

Regarding the mechanism of obtaining a good GaN thin film by intermittently supplying the raw material to the substrate in the present invention, the supply of the raw material is stopped to promote the diffusion of the raw material supplied to the substrate surface. It is presumed that this is because the two-dimensional growth of the GaN-based thin film was promoted. In fact, Ga
In the case of manufacturing an N-based thin film as a semiconductor component, particularly a light emitting device (LED) or a laser diode, a mixed crystal GaN-based thin film or a doped GaN-based thin film is combined to form a pn junction, a single hetero structure, or a double structure. A device having a heterostructure, a quantum well structure, a superlattice structure, or the like is manufactured.

[0021]

EXAMPLES The present invention will be described in more detail below with reference to examples.

[0022]

Example 1 Gas source MBE using ammonia gas
An example of forming a GaN thin film by the method will be described.
A gas source MBE provided with an evaporation crucible 2, a cracking gas cell 5, and a substrate heating holder 6 in a vacuum container 1 as shown in FIG. 1 was used as an apparatus.

Ga metal is put in the evaporation crucible 2 and 10
Heated to 20 ° C. A cracking gas cell 5 having alumina fibers filled therein is used to introduce the ammonia gas, heated to 400 ° C., and the ammonia gas is directly blown onto the substrate 7 to obtain 1 × 10 ¹⁸ / cm ² · s.
It was supplied at a beam intensity of ec. As the substrate 7, a surface obtained by rotating the sapphire R surface by 9.2 degrees about the R surface projection of the sapphire C axis was used. The off angle was 0.4 degrees or less. The size of the substrate was 20 mm square.

The pressure in the vacuum container is 1 × during film formation.
It was 10 ^-6 Torr. When the carbon-containing impurities at the time of film formation were measured by a quadrupole mass spectrometer 8, carbon monoxide was 2 ×.
At 10 ⁻⁸ Torr, carbon dioxide was 7 × 10 ⁻¹⁰ Torr.
First, the substrate 7 is heated at 900 ° C. for 15 minutes while supplying ammonia gas, and then the temperature is maintained at 850 ° C. to form a film. For film formation, first, the shutter of the Ga crucible is opened without supplying ammonia gas, and Ga for one atomic layer is supplied at a film forming rate of 1Å / sec. Next, close the shutter to stop the Ga supply and at the same time supply the ammonia gas,
After 20 seconds, the supply of ammonia gas is stopped again to form a Ga film. By repeating this, GaN with a film thickness of 0.7 μm
A thin film was prepared. When the electron density and the mobility of this GaN thin film were measured by the Van der Pauw method, they were 9 × 10 ¹⁸ / cm ³ and 120 cm ² / V · sec, respectively. Further, when cathodoluminescence was measured at 200 K, a spectrum having a peak near 3.5 eV was obtained as shown in FIG. In addition, observation by high-speed electron diffraction was performed during the thin film growth process. Film thickness 1
[1,2, -3,0] showing the crystal structure during film formation
FIG. 3 shows a diffraction pattern when an electron beam is incident in the direction. In FIG. 3, a streak pattern showing flatness on the atomic layer order can be seen.

[0025]

[Embodiment 2] Ga metal is put in the evaporation crucible 2 and 10
Heated to 20 ° C. A cracking gas cell 5 filled with alumina fibers was used to introduce the gas.
It was heated to 00 ° C., and the gas was directly blown onto the substrate 7 so that the gas was supplied with a beam intensity of 1 × 10 ¹⁸ / cm ² · sec.

As the substrate 7, a sapphire R surface having a size of 20 mm square and an off angle of 0.5 degrees or less is used. The pressure in the vacuum container was 2 × 10 ⁻⁶ Torr during film formation.
When the carbon-containing impurities at the time of film formation were measured by a quadrupole mass spectrometer 8, carbon monoxide was 1 × 10 ⁻⁸ Torr and carbon dioxide was 6 × 10 ⁻¹⁰ Torr.

First, the substrate 7 is heated at 900 ° C. for 15 minutes while supplying ammonia gas, and then the temperature is maintained at 750 ° C. to form a film. The film formation is performed by opening the shutter of the Ga crucible while supplying the ammonia gas from the cracking gas cell 5, and the film formation is performed at the film formation rate of 1Å / sec. The supply of Ga was stopped every time when one atomic layer was formed, and after a waiting time of 20 seconds, Ga was started to be formed again, and this was repeated to form a GaN thin film having a thickness of 0.8 μm.

The electron density and the mobility of this GaN thin film were measured by the Van der Pauw method.
It was × 10 ¹⁸ / cm ³ and 100 cm ² / V · sec. Further, when cathodoluminescence was measured at 200 K, a spectrum having a peak near 3.5 eV was obtained.

[0029]

[Embodiment 3] Ga metal is put in the evaporation crucible 2 and 10
Heated to 20 ° C. Magnesium metal was placed in the evaporation crucible 4 and heated to 310 ° C. A cracking gas cell 5 having alumina fibers filled therein was used to introduce the gas, and was heated to 300 ° C. to directly blow the gas onto the substrate 7 with a beam intensity of 1 × 10 ¹⁸ / cm ² · sec. Supplied.

As the substrate 7, a sapphire R surface having a size of 20 mm square and an off angle of 0.5 degrees or less is used. The pressure in the vacuum container was 2 × 10 ⁻⁶ Torr during film formation.
When the carbon-containing impurities at the time of film formation were measured by a quadrupole mass spectrometer 8, carbon monoxide was 2 × 10 ⁻⁸ Torr and carbon dioxide was 5 × 10 ⁻¹⁰ Torr.

First, the substrate 7 is heated at 900 ° C. for 15 minutes while supplying nitrogen trifluoride, and then maintained at a temperature of 700 ° C. to form a film. For film formation, while supplying nitrogen trifluoride from the cracking gas cell 5, the shutter for the Ga crucible and the shutter for the magnesium crucible are opened at the same time.
After supplying Ga for one atomic layer, both shutters were simultaneously closed to stop supplying Ga and Mg to the substrate for 20 seconds. After that, the shutter was opened again at the same time and the same procedure was repeated to form a doping thin film having a thickness of 1 μm.

The doping thin film thus produced was an insulator having a resistivity of 100 Ω · cm. Also, 200
When cathodoluminescence was measured at K, a spectrum having a peak near 3.5 eV was obtained.

[0033]

Example 4 Ga _1-x In _x by gas source MBE method
An example of producing an N mixed crystal thin film will be described. Ga metal was placed in the evaporation crucible 2 and heated to 1020 ° C., and In was placed in the evaporation crucible 3 and heated to 660 ° C. A cracking gas cell 5 having an alumina fiber filled therein is used for introducing gas, heated to 450 ° C., and blows the gas directly onto the substrate 7 to produce a gas of 2 × 10 ¹⁸ / cm ² ·.
It was supplied with a beam intensity of sec.

As the substrate 7, a sapphire R surface having a size of 20 mm square and an off angle of 0.5 degrees or less was used. The pressure in the vacuum container was 1 × 10 ⁻⁶ Torr during film formation.
The carbon-containing impurities at the time of film formation were measured by a quadrupole mass spectrometer 8. Carbon monoxide was 1 × 10 ⁻⁸ Torr, carbon dioxide was 6 × 10 ⁻¹⁰ Torr, and methane was 5 × 10 ⁻¹¹ Torr. there were.

First, the substrate 7 was heated at 900 ° C. for 15 minutes while supplying ammonia gas, and then the temperature was kept at 800 ° C. to form a film. Cracking gas cell 5 for film formation
The film was formed by opening the shutter of the crucible of Ga and In while supplying from the above. However, re-open the shutter after 30 seconds to stop the supply of Ga and In to the substrate by closing the shutter 16 of the crucible for each supplying Ga and In of 1 atomic layer, 0.8 [mu] m of Ga ₁ to repeat this _-x In _x N mixed crystal thin film (x
= 0.2) was produced.

When the carrier density and the mobility of this mixed crystal thin film were measured by the Van der Pau method, they were 8 × 10 ¹⁷ / cm ³ and 110 cm ² / V · sec, respectively. Further, when cathodoluminescence was measured at 200 K, a spectrum having a peak near 3.5 eV was obtained.

[0037]

Fifth Embodiment A gas source MBE equipped with an evaporation crucible 2, a cracking gas cell 5, and a substrate heating holder 6 was used as an apparatus in a vacuum container 1 as shown in FIG. Ga metal was placed in the evaporation crucible 2 and heated to 1020 ° C. A cracking gas cell 5 having alumina fibers filled therein was used to introduce the gas, and was heated to 400 ° C. to directly blow the gas onto the substrate 7 with a beam intensity of 1 × 10 ¹⁸ / cm ² · sec. Supplied.

As the substrate 7, a surface obtained by rotating the sapphire R surface by 9.2 degrees about the R surface projection of the sapphire C axis was used. The off angle used was 0.3 degrees or less. The size of the substrate was 20 mm square. The pressure in the vacuum container is
It was 3 × 10 ⁻⁶ Torr during film formation. When the carbon-containing impurities at the time of film formation were measured by a quadrupole mass spectrometer 8, carbon monoxide was 3 × 10 ⁻⁸ Torr and carbon dioxide was 7 × 1.
Was 0 ^{over 10} Torr.

First, the substrate 7 is heated at 900 ° C. for 15 minutes while supplying ammonia gas, and then the temperature is maintained at 750 ° C. to form a film. The film is formed by opening the shutter of the Ga crucible while supplying the ammonia gas from the cracking gas cell 5, and the film is formed at the film forming rate of 1Å / sec. After supplying one atomic layer of Ga, the supply of Ga is stopped, the supply of ammonia gas is stopped 20 seconds later, and the film formation of Ga is restarted 10 seconds later.
A μm GaN thin film was prepared.

When the carrier density and the mobility of this GaN thin film were measured by the Van der Pau method, they were 6 × 10 ¹⁸ / cm ³ and 130 cm ² / V · sec, respectively. Further, when cathodoluminescence was measured at 200 K, a spectrum having a peak near 3.5 eV was obtained.

[0041]

[Embodiment 6] Ga metal is put in the evaporation crucible 2 and 10
Heated to 20 ° C. A cracking gas cell 5 filled with alumina fibers was used to introduce the gas.
It was heated to 00 ° C., and the gas was directly blown onto the substrate 7 so that the gas was supplied with a beam intensity of 1 × 10 ¹⁸ / cm ² · sec.

As the substrate 7, a sapphire R surface having a size of 20 mm square and an off angle of 0.4 degrees or less was used. The pressure in the vacuum container was 2 × 10 ⁻⁶ Torr during film formation.
When the carbon-containing impurities at the time of film formation were measured by a quadrupole mass spectrometer 8, carbon monoxide was 2 × 10 ⁻⁸ Torr and carbon dioxide was 6 × 10 ⁻¹⁰ Torr.

First, the substrate 7 is heated at 900 ° C. for 15 minutes while supplying ammonia gas, and then the temperature is maintained at 850 ° C. to form a film. For film formation, first open the shutter of the Ga crucible without supplying ammonia gas, and 1 Å / sec
Ga of one atomic layer is supplied at the film forming rate of. Next, the shutter is closed to stop the supply of Ga and simultaneously supply the ammonia gas. After 20 seconds, the supply of the ammonia gas is stopped again and after 10 seconds, the Ga is supplied again. By repeating this, a GaN thin film having a thickness of 0.7 μm was produced.

When the carrier density and the mobility of this GaN thin film were measured by the Van der Pauw method, they were 7 × 10 ¹⁸ / cm ³ and 180 cm ² / V · sec, respectively. Further, when cathodoluminescence was measured at 200 K, a spectrum having a peak near 3.5 eV was obtained. Furthermore, while forming a film [1,
An electron beam was incident from the [2, -3, 0] direction and observation was performed by high-speed electron beam diffraction. As a result, a streak pattern indicating that the film surface was flat on the atomic layer order was observed at the time of film formation of about 500 Å.

[0045]

According to the GaN-based thin film manufacturing method of the present invention, since the crystallinity of the film can be improved, the carrier density can be reduced and the film flatness can be improved.
An excellent GaN-based thin film for semiconductor light emitting device can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic view of a gas source MBE apparatus used for thin film production.

FIG. 2 is a spectrum diagram showing a measurement result of cathodoluminescence.

3 is a graph of the nitrogen gallium thin film 100 obtained in Example 1. FIG.
It is a high-speed electron diffraction photograph showing a crystal structure at the time of 0Å film formation.

[Explanation of symbols]

 1. Vacuum container 2. Evaporating crucible 3. Evaporating crucible 4. Crucible for evaporation 5. Gas cell 6. Substrate heating holder 7. Substrate 8. Quadrupole mass spectrometer 9. Cryopanel 10. Valve 11. Cold trap 12. Oil diffusion pump 13. Oil rotary pump 14. Shutter 15. Shutter 16. shutter

[Procedure amendment]

[Submission date] October 29, 1991

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

[Figure 3]

Claims (3)

[Claims] 1. I on a substrate using a gas source MBE method
A method for growing a gallium nitride-based thin film, which comprises alternately supplying a group II element and a group V element. 2. A method for growing a gallium nitride-based thin film, which comprises intermittently supplying a group III element while continuously supplying a group V element using a gas source MBE method. 3. A method for growing a gallium nitride-based thin film, which comprises providing a time during which a raw material is not supplied to a substrate during the growth of the thin film when the gallium nitride thin film is formed by using the gas source MBE method.