JP2002373823A - Thin-film manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technology for forming a group-III nitride based thin magnetic semiconductor film. SOLUTION: After an AIN layer 22 is formed on the surface of a substrate 21, a buffer layer 23 is formed of a GaN-based thin film on the surface of the AIN layer; and nitrogen-atom containing gas such as ammonia gas is introduced into the surface of the buffer layer 23 to carry out pyrolysis, and irradiation with molecular rays of a group-III element and molecular rays of a magnetic impurity element is carried out to a thin semiconductor thin film 24. The thin semiconductor thin film 24 shows ferromagnetism at room temperature. Further, GaN and Mn are a p-type at room temperature, so they are usable for a p-type layer of a semiconductor element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for growing a dilute magnetic semiconductor, and more particularly to a technique of using a group III metal such as Ga or Al as a main component and Mn, V, Cr,
The present invention relates to a technique for growing a group III nitride diluted magnetic semiconductor mainly containing Fe, Ni, or the like by a molecular beam epitaxy method.

[0002]

2. Description of the Related Art In recent years, elements utilizing the giant magnetoresistance effect in a metal multilayer film have been put to practical use, and magnetic sensors and magnetic random access memories have been actively studied.

[0003] Further, application of new materials such as a composite structure of a magnetic substance and a semiconductor and a diluted magnetic semiconductor to electronics has been studied. Here, the diluted magnetic semiconductor is a mixed crystal semiconductor of a non-magnetic semiconductor and a magnetic atom, and generally indicates a semiconductor having a magnetic atom concentration of 20 at% or less.

As a diluted magnetic semiconductor, GaAs: Mn, InAs: Mn, Cd
Te: Mn and the like are realized, and in GaAs: Mn, a light emitting diode using a pn junction formed with n-GaAs using this as a p-layer has been manufactured.
When a current was applied to the light emitting diode at a temperature lower than the Curie temperature of the GaAs: Mn layer to emit light, it was confirmed that the light emission had a circularly polarized component based on the spin-polarized current. This indicates that a spin-polarized current flowed through the pn junction (Y. Ohno, et al., NATURE, vol. 40).
2, 1999).

However, none of these existing diluted magnetic semiconductors whose Curie temperature can exceed room temperature has been synthesized yet.

Further, in some theoretical predictions, there is no report that these existing diluted magnetic semiconductors have a Curie point exceeding room temperature (T. Dietl, et al., SCIE
NCE, vol.287, 2000).

On the other hand, when GaN which is a wide band gap semiconductor is used as a base material, Mn, V, Cr
Has been predicted to exhibit ferromagnetism containing as a magnetic impurity element, and its Curie temperature exceeds room temperature. In addition, since they are transparent in the visible light region, they are considered promising as transparent room-temperature ferromagnetic semiconductors.

[0008] Until now, a group of Tokyo Institute of Technology
GaN: Mn, Ga by f-excited nitrogen plasma MBE
Attempts have been made to grow N: Fe, but it has not yet reached ferromagnetism even in a low-temperature region.

[0009]

SUMMARY OF THE INVENTION The present invention realizes a diluted magnetic semiconductor that exhibits ferromagnetism at room temperature. In order to solve the low Curie temperature which is a problem in the conventional diluted magnetic semiconductor, it is an object of the present invention to provide a method for forming a diluted magnetic semiconductor thin film as a component such as a device using spin polarization operating at room temperature. It is an issue.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises placing a substrate in a vacuum atmosphere, containing a magnetic impurity element, and containing a group III element and nitrogen as main components. A thin film manufacturing method for forming a diluted magnetic thin film made of a material on the substrate, wherein a nitrogen-containing atomic gas containing nitrogen atoms is introduced into the vacuum atmosphere, and the nitrogen-containing atomic gas is placed on the substrate or the substrate. A thin film manufacturing method for irradiating the substrate with a molecular beam of the group III element and the magnetic impurity element while performing photolysis or thermal decomposition in the vicinity to grow the diluted magnetic thin film. The invention according to claim 2 is the thin film manufacturing method according to claim 1, wherein the diluted magnetic thin film uses gallium, aluminum, or indium as a group III element. The invention according to claim 3 is the method according to claim 1 or 2, wherein any one or more of manganese, vanadium, chromium, iron, and nickel is used as the magnetic impurity element. It is. The invention according to claim 4 is the thin film manufacturing method according to any one of claims 1 to 3, wherein at least one of ammonia gas and hydrazine gas is used as the nitrogen-containing atomic gas. . The invention according to claim 5 is to form a buffer layer made of a material containing a group III element and nitrogen as main components on the substrate, and then grow the diluted magnetic thin film on the surface of the buffer layer. A thin film manufacturing method according to any one of claims 1 to 4. The invention according to claim 6 is the thin film manufacturing method according to claim 5, wherein the buffer layer contains gallium and nitrogen as main components.
The invention according to claim 7, wherein the substrate is a sapphire substrate, and after forming an aluminum nitride layer on the surface of the sapphire substrate, the buffer layer is formed on the surface of the aluminum nitride layer. It is. The invention according to claim 8 is the method according to claim 5, wherein the buffer layer contains aluminum and nitrogen as main components. The invention according to claim 9 is a diluted magnetic thin film formed on a substrate, wherein the substrate is placed in a vacuum atmosphere containing a nitrogen-containing atomic gas having nitrogen atoms in its structure, This is a diluted magnetic thin film grown by irradiating a molecular beam of a group III element and a magnetic impurity element onto the substrate while the gas is subjected to photolysis or thermal decomposition. The invention according to claim 10 is the diluted magnetic thin film according to claim 9, wherein the group III element is gallium, and the magnetic impurity element is manganese. The invention according to claim 11 is the diluted magnetic thin film according to claim 9, wherein the group III element is aluminum and the magnetic impurity element is manganese. According to a twelfth aspect of the present invention, there is provided a gallium nitride film containing manganese, wherein the p-type gallium nitride film contains the manganese at 2 atomic% or more and has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more. . The invention according to claim 13 is an aluminum nitride film containing manganese, which is a p-type aluminum nitride film containing 3 at% or more of manganese and having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more. .

The present invention is configured as described above,
This is a manufacturing method in which a diluted magnetic semiconductor thin film containing a Group I element and nitrogen as main components and containing a magnetic impurity element is formed on a substrate.

In the present invention, as a source of nitrogen atoms for growing a diluted magnetic semiconductor thin film on the surface of a buffer layer,
Nitrogen-containing gas such as ammonia and hydrazine is photo-decomposed or thermally decomposed to generate nitrogen atoms. Here, the process of photolysis or the process of thermal decomposition is performed on or near the substrate.

As long as it is a nitrogen-containing atomic gas capable of supplying nitrogen atoms by photolysis or thermal decomposition, other compounds such as ammonia and hydrazine can also be used. In the case of ammonia, the flow rate is 5 to 100 sccm. The substrate temperature when forming the diluted magnetic semiconductor thin film is 550 ° C. or more and 800 ° C. or less.

The nitrogen-containing atomic gas may be constituted by one kind of gas such as ammonia or hydrazine, or two or more kinds may be mixed to form a nitrogen-containing atomic gas.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Embodiments of the present invention will be described below with reference to the drawings. Reference numeral 10 in FIG. 1 indicates a molecular beam epitaxy apparatus that can be used in the present invention.

The molecular beam epitaxy apparatus 10 has a vacuum chamber 11, and a gas introduction nozzle 13 and first and second evaporation sources 14 and 15 are arranged on the bottom wall side. . On the ceiling side of the vacuum chamber 11, a heater 17 is arranged.

In the first and second evaporation sources 14 and 15, a first metal material 36 containing Ga as a main component and a Mn
The second metal material 37 having as a main component is disposed.

Reference numeral 21 in FIG. 1 indicates a sapphire substrate on which a film is to be formed. The sapphire substrate 21 has a sapphire C surface 28 exposed on the surface.

First, a sapphire substrate 21 for forming a film is
The sapphire C surface was arranged near the heater 17 with the sapphire C surface facing the bottom wall of the vacuum chamber 11.

Reference numeral 21 in FIG. 2A indicates the sapphire substrate, and reference numeral 28 indicates the sapphire C surface of the sapphire substrate 21.

In this state, the heater 17 is energized to generate heat, the sapphire substrate 21 is heated to 950 ° C. to perform a cleaning process, then cooled to 900 ° C., and ammonia gas is introduced from the gas nozzle 13 into the vacuum chamber 11. , Sapphire C
When sprayed on the surface 28, AlN nuclei are deposited, and the AlN layer 22 is formed (FIG. 2A).

The flow rate of ammonia gas is 5 to 100 scc.
m, and the spray time was 5 to 30 minutes, the AlN layer was formed under any conditions.

Next, the temperature of the sapphire substrate 21 is set to 55
The temperature was lowered to 0 ° C., and ammonia gas was ejected from the gas nozzle 13 and sprayed on the surface of the AlN layer 22, and the first metal material 36 in the first evaporation source 14 was heated to obtain Ga.
When a metal molecular beam (vapor of the first metal material 36 containing Ga as a main component) is generated and irradiated on the surface of the AlN layer 22, a buffer layer composed of a GaN thin film is formed on the surface of the AlN layer 22. Is done. Reference numeral 23 in FIG. 2B indicates the buffer layer.

The flow rate of ammonia gas is 5-100 scc
m, the temperature of the first deposition source is in the range of 850 to 950 ° C. to form a buffer layer, and the thickness of the buffer layer is 0.1 to 1 μm.
Was used.

After forming the buffer layer 23 to a predetermined thickness,
The temperature of the sapphire substrate 21 is increased to 720 ° C., and a nitrogen-containing atomic gas (here, an ammonia gas) is directly blown onto the surface of the buffer layer 23 by the gas nozzle 13 to thermally decompose the sapphire substrate 21. First and second
Are heated, and the molecular beam containing Ga as a main component (the first metal material 36 containing Ga as a main component) is heated.
Is irradiated to the buffer layer 23, and a molecular beam containing Mn as a main component (steam of the second metal material 37 containing Mn as a main component) is directed toward the buffer layer 23.
A diluted magnetic semiconductor thin film composed of an N: Mn film is formed.
Reference numeral 24 in FIG. 2C indicates the diluted magnetic semiconductor thin film.

A GaN: Mn film having a thickness of 0.1 to 1 μm was grown under the following conditions. Temperature 850-9 of first vapor deposition source
50 ° C., temperature of the second evaporation source 475 to 630 ° C., flow rate of ammonia gas 5 to 100 sccm.

The Mn content of the obtained GaN: Mn film was set to E
PMA (Electron Probe Micro)
(Analyser), 0.5 to 15a
t%. The Mn content did not depend on the flow rate of ammonia.

In addition, Hall measurement of the GaN: Mn film
and der Pauw method (Nihon Biorat HL
5500PC), it showed p-type conductivity, and the carrier concentration was 2 × 10 ^{17 to} 5 × 10 ¹⁹ (cm ⁻³ ).
Met. When the Mn concentration is 0.5 at%, 3 at%, and 15 at%, the carrier concentrations are 2 × 10 ¹⁷ and 4 ×, respectively.
It was 10 ¹⁸ , 5 × 10 ¹⁹ cm ^-3 . FIG. 3 shows the relationship between the Mn content and the carrier concentration of the obtained GaN: Mn film.

Since the obtained GaN: Mn film shows p-type, it is not a ferromagnetic film but a bipolar transistor,
It can also be used as a p-type layer of a semiconductor element such as a light emitting diode and a laser.

Magnetic measurements of these films using SQUID at room temperature showed ferromagnetism. FIG. 4 shows a magnetization curve of a GaN: Mn film having a Mn concentration of 3%. The five curves show temperatures of 1.8K, 4.2K, 8.0K, and 1K, respectively.
It is a magnetization curve at 2K and 300K.

In the above, the AlN layer 2 is placed in the same vacuum chamber 11.
2, the GaN-based thin film buffer layer 23, and the diluted magnetic semiconductor thin film 24 are formed, but they may be formed in different vacuum chambers 11.

Further, Ga is directly formed without forming the AlN layer 22.
The buffer layer 23 of an N-based thin film may be formed.

The AIN layer 22 and the buffer layer 23 made of a GaN-based thin film can be formed by various growth methods such as MBE, sputtering, CVD, and laser deposition.

Example 2 Using the same molecular beam epitaxy apparatus 10 as in Example 1, a thin magnetic semiconductor thin film was formed as follows. Here, a metal material 38 containing Al as a main component is disposed in the third evaporation source 16.

First, as in the first embodiment, the sapphire substrate to be formed was placed near the heater 17 with its sapphire C surface facing the bottom wall of the vacuum chamber 11.

Reference numeral 61 in FIG. 5A indicates the sapphire substrate, and reference numeral 68 indicates the sapphire C surface of the sapphire substrate 61.

In this state, the heater 17 is energized to generate heat, the sapphire substrate 61 is heated to 950.degree. C. for cleaning, and then cooled to 900.degree.
At that temperature.

Next, ammonia gas is introduced from the gas nozzle 13 and the sapphire C surface 68 of the sapphire substrate 61 is introduced.
To form an AIN layer having a predetermined thickness on the sapphire C surface 68. Reference numeral 62 in FIG. 5A indicates the AlN thin film.

The flow rate of ammonia gas is 5 to 100 scc
m, and the spray time was 5 to 30 minutes, the AlN layer was formed under any conditions.

Next, the temperature of the sapphire substrate 61 is lowered to 760 ° C., a nitrogen-containing gas is introduced from the gas nozzle 13 into the vacuum chamber 11, and is directly blown onto the surface of the AlN layer 62 to be thermally decomposed. A molecular beam mainly composed of Mn is emitted toward the surface of the AlN layer 62, and simultaneously, a molecular beam mainly composed of Mn is extracted from the second evaporation source 15 by A.
When irradiation is performed toward the 1N layer 62, a dilute magnetic semiconductor thin film composed of an AlN: Mn film is formed on the surface of the AlN layer 62.

Reference numeral 64 in FIG. 5B indicates the diluted magnetic semiconductor thin film.

An AlN: Mn film having a thickness of 0.1 to 1 μm was grown under the following conditions. Third deposition source temperature 850-1
000 ° C., the temperature of the second deposition source is 475 to 680 ° C., and the flow rate of ammonia gas is 5 to 100 sccm.

The Mn content of the obtained AlN: Mn film was E
It was 0.5-15 at% as measured by PMA. The Mn content did not depend on the flow rate of ammonia.

In addition, Hall measurement of the AlN: Mn film
and der Pauw method (Nihon Biorat HL
5500PC), it showed p-type conductivity and the carrier concentration was 1 × 10 ¹⁷ to 1 × 10 ¹⁹ (cm ⁻³ ).
Met. Mn concentration of 1 atomic%, 6 atomic%, 15 atomic%
, The carrier concentrations are 1 × 10 ¹⁷ and 5 × 10 ¹⁷ , respectively.
¹⁷ and 1 × 10 ¹⁹ cm ⁻³ . FIG. 6 shows the obtained Al
N: Relationship between Mn content of Mn film and carrier concentration.

Since the obtained AlN: Mn film shows p-type, it is not a ferromagnetic film but a bipolar transistor.
It can also be used as a p-type layer for light emitting diodes, lasers, and the like.

<Other Embodiments> The Dilute Magnetic Semiconductor Thin Film 2
4 and 64 were formed on the sapphire C surfaces 28 and 68,
A surface other than the sapphire substrate C surface may be used. Also, S
An iC substrate, a GaN substrate, a Si substrate, a GaAs substrate, or the like can be used.

In the above embodiment, manganese (Mn) was used as the magnetic impurity contained in the diluted magnetic semiconductor thin film. However, instead of manganese, a material mainly containing V, Cr, Fe, Ni or the like was used as the second impurity. Example 1 placed in the vapor deposition source 15
It has been confirmed that a dilute magnetic semiconductor thin film can be formed even by performing the same steps as in Steps 2 and 3.

As described above, according to the present invention, a group III nitride composed of a group III element and a nitrogen atom is once formed on the surface of a film-forming target, and a nitrogen atom such as an ammonia gas or a hydrazine gas is chemically formed. The nitrogen-containing gas contained in the structure is introduced into a vacuum atmosphere, and photolysis or thermal decomposition is performed to introduce nitrogen atoms to the surface of the group III nitride. A thin magnetic semiconductor thin film is manufactured by irradiating the surface of a film formation target.

In short, the present invention does not use nitrogen plasma at the time of forming a diluted magnetic semiconductor thin film, but rather photo-decomposes or thermally decomposes nitrogen-containing atoms into a nitrogen source, which is combined with a molecular beam of a group III element and a molecular beam of a magnetic impurity element. And a method of forming a diluted magnetic semiconductor thin film.

The GaN or A formed as described above
The 1N-based diluted magnetic semiconductor thin films 24 and 64 are formed of a desired type of electronic device, optoelectronic device, isolator,
It can be used by being incorporated in a magnetic random access memory (MRAM) or the like. Table 1 below shows the structures of the substrate and the diluted magnetic semiconductor thin film that can be formed by the method of the present invention.

[0051]

[Table 1]

Since the obtained diluted magnetic semiconductor thin film shows p-type, it can be used not only as a ferromagnetic film but also as a p-type layer of a bipolar transistor, a light emitting diode, a laser, or the like.

In the table, "Surface nitrided AlN / GaN" in the column of "buffer layer" means that the surface of the substrate is nitrided to obtain AlN / GaN.
In this case, a buffer layer is formed by forming a GaN thin film on the surface of the AlN layer after forming the N layer.

[0054]

According to the present invention, it is possible to manufacture a device having room temperature ferromagnetism that cannot be achieved by the existing diluted magnetic semiconductor thin film and operating at room temperature as a component. A dilute magnetic semiconductor thin film exhibiting ferromagnetism at room temperature can be obtained without performing a heat treatment or the like after growth.

[Brief description of the drawings]

FIG. 1 shows an example of a molecular beam epitaxial apparatus that can be used in the present invention.

FIGS. 2A to 2C are diagrams for explaining a step of forming a diluted magnetic thin film according to an example of the method of the present invention.

FIG. 3 is a graph showing the relationship between the Mn content of a GaN: Mn film and the carrier concentration.

FIG. 4 is a graph showing a magnetization curve of a GaN: Mn film having a Mn concentration of 3%.

FIGS. 5A and 5B are diagrams for explaining a process of forming a diluted magnetic thin film according to another example of the method of the present invention.

FIG. 6 is a graph showing the relationship between the Mn content of the AlN: Mn film and the carrier concentration.

[Explanation of symbols]

 21, 61 sapphire substrate 22, 62 AlN layer 23 buffer layer 24, 64 diluted magnetic semiconductor thin film 28, 68 sapphire C-plane

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K029 AA04 BA58 BB02 BC06 BD01 CA01 5E049 CC08 EB06 HC05 JC01 MC01 5F103 AA04 DD01 HH03 HH04 JJ01 KK10 LL02 LL03 LL20 NN01 NN06 PP02

Claims (13)

[Claims] 1. A method for manufacturing a thin film, comprising: placing a substrate in a vacuum atmosphere; and forming a diluted magnetic thin film comprising a material containing a magnetic impurity element and containing a group III element and nitrogen as main components on the substrate. Introducing a nitrogen-containing atomic gas containing nitrogen atoms into the vacuum atmosphere, and performing photolysis or thermal decomposition of the nitrogen-containing atomic gas on or in the vicinity of the substrate, thereby forming the III on the substrate.
A thin film manufacturing method for irradiating a molecular beam of a group III element and the magnetic impurity element to grow the diluted magnetic thin film. 2. The thin film manufacturing method according to claim 1, wherein said diluted magnetic thin film uses gallium, aluminum or indium as a group III element. 3. The magnetic impurity element according to claim 1, wherein at least one of manganese, vanadium, chromium, iron, and nickel is used.
Item. 4. The method according to claim 1, wherein at least one of ammonia gas and hydrazine gas is used as the nitrogen-containing atomic gas. 5. A buffer layer comprising a material containing a group III element and nitrogen as main components is formed on the substrate, and the diluted magnetic thin film is grown on the surface of the buffer layer.
The method for producing a thin film according to claim 1. 6. The method according to claim 5, wherein said buffer layer contains gallium and nitrogen as main components. 7. The method according to claim 6, wherein a sapphire substrate is used as the substrate, and after forming an aluminum nitride layer on the surface of the sapphire substrate, the buffer layer is formed on the surface of the aluminum nitride layer. 8. The method according to claim 5, wherein the buffer layer contains aluminum and nitrogen as main components. 9. A thin magnetic thin film formed on a substrate, wherein the substrate is placed in a vacuum atmosphere containing a nitrogen-containing atomic gas having nitrogen atoms in its structure, and the nitrogen-containing atomic gas is irradiated with light. A diluted magnetic thin film grown by being decomposed or thermally decomposed and irradiated with a molecular beam of a group III element and a magnetic impurity element on the substrate. 10. The thin magnetic thin film according to claim 9, wherein the group III element is gallium, and the magnetic impurity element is manganese. 11. The group III element is aluminum,
The diluted magnetic thin film according to claim 9, wherein the magnetic impurity element is manganese. 12. A p-type gallium nitride film containing manganese, wherein the p-type gallium nitride film contains 2 atomic% or more of manganese and has a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more. 13. A p-type aluminum nitride film containing manganese, wherein the manganese is contained at 3 atomic% or more and the carrier concentration is 1 × 10 ¹⁷ cm ^-3 or more.