JPH1012624A - Thermal processing method of nitride compound semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal processing method of a nitride compound semiconductor that ensures a p type nitride compound semiconductor having a higher carrier concentration compared with the prior art. SOLUTION: After a nitride compound semiconductor such as GaN where an acceptor impurity such as Mg is doped is grown by an organic metal chemical vapor growing method, in an atmosphere comprising inert gas such as nitrogen containing hydrocarbon that does not release nitrogen in a nitrogen release process the nitride compound semiconductor is thermally processed. For the nitrogen containing hydrocarbon, a material which contains a hydro group, an alkyl group and/or a phenyl group combined with nitrogen, having the number of the hydro groups being less than the sum of the number of the alkyl group and the number of the phenyl group for example, trimethylamine, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat-treating a nitride-based compound semiconductor, and more particularly, to a nitride-based compound such as GaN doped with an acceptor impurity such as Mg.
It is suitable for heat treatment for activating acceptor impurities in a group V compound semiconductor.

[0002]

2. Description of the Related Art Nitride (nitride) -based III-V compound semiconductors such as GaN, AlGaN, and GaInN have band gaps ranging from 1.8 eV to 6.2 eV, and emit red to ultraviolet light. In recent years, attention has been paid to the realization of a possible light-emitting element because it is theoretically possible.

When a light emitting diode (LED), a semiconductor laser, or the like is manufactured from the nitride III-V compound semiconductor, AlGaN, GaInN, GaN, or the like is laminated in multiple layers, and the light emitting layer (active layer) is n. It is necessary to form a structure sandwiched between the mold cladding layer and the p-cladding layer.

Conventionally, metal organic chemical vapor deposition (MO)
For example, to grow a p-type GaN layer by a vapor phase growth method such as a CVD method, a hydrogen (H ₂ ) carrier gas or H
_In a mixed gas of ₂ and nitrogen (N ₂ ), for example, G
a trimethylgallium (TMG, Ga (C
H ₃ ) ₃ ), ammonia (NH ₃ ) as a N source and cyclopentadienyl magnesium (Cp ₂ Mg) as a p-type dopant are applied to a heated substrate, for example, a sapphire substrate, a SiC substrate, a GaAs substrate, or the like. To grow a Mg-doped GaN layer by a thermal decomposition reaction. Since the Mg-doped GaN layer immediately after the growth is a high-resistance layer, it is made into a p-type by performing a heat treatment in a vacuum or in an inert gas. in this case,
By this heat treatment, H incorporated in the GaN crystal is desorbed, whereby Mg in the GaN is activated to generate carriers and become p-type.

[0005]

However, at present, the carrier concentration of the p-type GaN layer obtained as described above is at most about 3 × 10 ¹⁷ cm ^-3 and its resistivity is as high as about 2 Ωcm. For this reason, for example, nitride III
In a semiconductor laser using a -V compound semiconductor,
There were the following problems. First, in this semiconductor laser, a p-type GaN layer is used as a contact layer of a p-side electrode. However, since the resistance of the p-type GaN layer is high, a large voltage loss occurs in the p-type GaN layer during high-current operation. Is to happen. Second, since the carrier concentration of the p-type GaN layer is low, the contact resistance between the p-type GaN layer and the p-side electrode is as high as about 10 ⁻² Ωcm ² , so that a typical injection current in a semiconductor laser is Density of 1 kA / cm
At the time of operation at ² , the voltage loss of about 10 V occurred at the interface between the p-type GaN layer and the p-side electrode, and the laser characteristics deteriorated.

The above is about p-type GaN.
A similar problem may exist when obtaining a p-type nitride-based III-V compound semiconductor other than N, more generally a nitride-based compound semiconductor.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for heat-treating a nitride-based compound semiconductor capable of obtaining a p-type nitride-based compound semiconductor having a higher carrier concentration than in the prior art.

[0008]

Means for Solving the Problems The present inventor has made intensive studies in order to solve the above-mentioned problems of the prior art. The outline is as follows.

As described above, only by growing the Mg-doped GaN layer, a p-type GaN having a low carrier concentration and a high resistivity is obtained.
The reason why only a layer is obtained is that hydrogen taken into the crystal during growth exists near Mg, and Mg is inactivated by interaction with the hydrogen. The holes are generated by the heat treatment because the hydrogen is desorbed to activate Mg, which acts as an acceptor impurity. On the other hand, in the p-type GaN layer grown by the molecular beam epitaxy (MBE) method, hydrogen is not taken into the crystal at the time of growth, so that even if the heat treatment for activating the acceptor impurity is not performed, 5 × 10 5 ^A hole concentration of ¹⁸ cm ^-3 or more has been obtained.

[0010] By the way, even in the above-mentioned conventional heat treatment method, by extending the heat treatment time or increasing the heat treatment temperature to desorb hydrogen taken in the crystal, the p-type nitride-based compound semiconductor is removed. Can be increased and the resistivity can be reduced. However,
If a long-time or high-temperature heat treatment is performed to sufficiently desorb the hydrogen taken into the crystal, there is a problem that the crystal itself is deteriorated mainly by the desorption of nitrogen.

Therefore, if the deterioration of the crystal is suppressed, the hydrogen in the crystal can be reduced by 100% by a long-time or high-temperature heat treatment.
%, It is expected that a hole concentration comparable to that of a p-type GaN layer grown by MBE can be obtained.

Thus, the present inventors have conducted various studies. As a result, in order to obtain a p-type nitride compound semiconductor having a high carrier concentration, active hydrogen is not generated during the heat treatment for activating the acceptor impurities. It was found that it was effective to do so, and it was found that the selection of the atmosphere gas for the heat treatment was extremely important for that purpose, and the following conclusion was reached.

1. The carrier gas should be used other than H _2. This is because H ₂ is taken into the grown crystal and inactivates Mg used as a p-type impurity. As such a carrier gas, specifically, argon (Ar), helium (H
e), there is such as N _2. In terms of price, N of these
₂ is the cheapest.

2. The atmosphere gas for the heat treatment contains a nitrogen-containing hydrocarbon that does not release hydrogen during the nitrogen release process during decomposition. This does not mean that the nitrogen-containing hydrocarbon does not contain a hydro group (-H). If in one molecule are present and a methyl group (-CH ₃₎ and a hydro group (-H), they probability of forming a stable methane (CH ₄₎ is very high coalesce. Therefore, a necessary condition for the molecule of the nitrogen-containing hydrocarbon is that the number of hydro groups is equal to or less than the number of methyl groups. For example, trimethylhydrazine ((CH ₃ )
_{2 N-NH (CH 3)} ) is as _{(CH 3) 2 N-NH} (CH 3) → · N (CH 3) 2 + · NH (CH 3) → 2N + C 2 H 6 + CH 4 (1) Decomposes and does not release hydrogen.

3. Next, the nitrogen-containing hydrocarbons consider the case having an ethyl group (-C ₂ H ₅₎ instead of the methyl group. For example, diethylamine (HN <(C ₂ H ₅ )
_{In 2} ), a decomposition reaction of HN <(C ₂ H ₅ ) ₂ → NH ₃ + 2C ₂ H ₄ (2) can be considered. Further, a decomposition reaction of HN <(C ₂ H ₅ ) ₂ → N—C ₂ H ₅ + C ₂ H ₆ → NH + C ₂ H ₆ + C ₂ H ₄ (3) is also conceivable. These are all reactions that generate hydrogen. Here, in the formulas (2) and (3), ethylene (C ₂ H ₄ ) is generated.
The ethylenic elimination reaction of the ethyl group is β-elimin
It is known that this phenomenon is very likely to occur in organometallic compounds such as triethylgallium (TEG, Ga (C ₂ H ₅ ) ₃ ). However, in an ethyl compound with a group V element such as As or N,
It is considered that this β-elimination decomposition detachment is unlikely to occur (for example, Appl. Organometal Chem. Vo
l.5, 331 (1991)). In this case, the decomposition reaction is as follows: HN <(C ₂ H ₅ ) ₂ → N + C ₂ H ₆ + · C ₂ H ₅ (4) Since no hydrogen is generated, the ethyl group may be regarded as the same as the methyl group. Furthermore, other alkyl groups may be regarded as the same as the methyl group by the same consideration.

4. There is an aromatic cyclic hydrocarbon having a phenyl group (C ₆ H ₅ −) as a hydrocarbon that does not cause β-elimination. This aromatic cyclic hydrocarbon is very stable, and its decomposition energy is very large. One of the aromatic cyclic hydrocarbons, an amine having a phenyl group bonded to nitrogen, for example, phenylmethylamine (C
_{6 H 5 -NH (CH 3)} ) decomposition reaction _{C 6 H 5 -NH (CH 3} ) → C 6 H 5 -N + CH 4 → N + CH 4 + · C 6 H 5 (5) next to, does not release hydrogen . In this sense, a phenyl group can be considered equivalent to a methyl group. The same applies to higher aromatic cyclic hydrocarbons such as naphthalene, but these are generally disadvantageous in that their vapor pressures are low.

5. From the above considerations, p of high carrier concentration
Examples of the nitrogen-containing hydrocarbon used in the atmosphere during the heat treatment for obtaining the type III-V compound semiconductor include the following. That is, now, an alkyl group or a phenyl group the R (-C ₆ H _5), a hydro group of H (-
H), NR ₃ , NHR as amine compounds
Such as _2, as the azo compounds RN = NR, HN = NR
Hydrazine compounds such as R ₂ N—NH ₂ , R
_{2'N-NHR, R 2'N} -NH 2, etc. RHN-NRH, as the azide compound, and the like R-N _3.

6. Next, the growth of a nitride-based III-V compound semiconductor will be considered, and restrictions on the group III element materials used at that time will be considered. First, for example, trimethylgallium (TMG, Ga (CH ₃ ) ₃ ) can be used because it does not release hydrogen during decomposition.

Next, triethyl gallium (TEG, Ga
(C ₂ H ₅ ) ₃ ) is decomposed by the β-elimination reaction like Ga (C ₂ H ₅ ) ₃ → GaH ₃ +3 C ₂ H ₄ (6) to generate galan (GaH ₃ ) and grow hydrogen. Leave on the surface. In this sense, TEG is not preferred. However, since the group V material is generally supplied several hundred times in excess of the group III material, for example, when trimethylamine is used as the nitrogen material, GaH
Several hundred times a methyl group ₃ becomes be present theoretically consumes hydrogen GaH _3. Therefore, the generation of hydrogen from the group III raw material can be ignored since the supply amount of the group III raw material is overwhelmingly small.

Next, it is clear that gallium chloride (GaCl) used in a chloride method or the like can be used. From the above, it can be said that there is substantially no limitation on the group III raw material.

The present invention has been made based on the above considerations by the present inventor. That is, in order to achieve the above object, the present invention provides a method for heat-treating a nitride-based compound semiconductor in which a nitride-based compound semiconductor doped with an acceptor impurity is activated by heat-treating the nitride-based compound semiconductor. The nitride-based compound semiconductor is heat-treated in an atmosphere containing a nitrogen-containing hydrocarbon that does not release hydrogen in the release process.

In the present invention, typically, the nitride-based compound semiconductor is heat-treated in an atmosphere containing an inert gas and a nitrogen-containing hydrocarbon. As the inert gas, for example, Ar, He, N ₂ or the like is used.

In the present invention, the nitrogen-containing hydrocarbon is
Typically, it contains a hydro group bound to nitrogen and an alkyl group and / or a phenyl group, and the number of hydro groups is equal to or less than the sum of the number of alkyl groups and the number of phenyl groups. . Such nitrogen-containing hydrocarbons are, specifically, the above-mentioned amine compounds, azo compounds, hydrazine compounds, azide compounds, and the like. An appropriate one is selected according to the type and the like. Particularly, as the amine compound, trimethylamine, dimethylamine, triethylamine, diethylamine and the like are preferably used.

In the present invention, typically, the nitride-based compound semiconductor is a nitride-based III-V compound semiconductor comprising at least one group III element selected from the group consisting of Al, Ga and In and N and N. It is. Some specific examples of the nitride III-V compound semiconductor include GaN, AlGaN, and GaInN.

In the present invention, the acceptor impurities doped into the nitride-based compound semiconductor include Group II elements,
For example, Mg, Zn, Cd or the like is used.

In the present invention, typically, the nitride-based compound semiconductor to be heat-treated is one grown by vapor phase metalorganic chemical vapor deposition.

In the heat treatment method for a nitride-based compound semiconductor according to the present invention, the nitride-based compound semiconductor is heat-treated in an atmosphere containing a nitrogen-containing hydrocarbon which does not release hydrogen during the nitrogen release process. By doing so, it is possible to prevent nitrogen from desorbing from the nitride-based compound semiconductor during the heat treatment, and to suppress the deterioration of the crystal of the nitride-based compound semiconductor due to the desorption of nitrogen. For this reason, heat treatment at a higher temperature can be performed for a longer period of time, so that the hydrogen taken into the crystal of the nitride-based compound semiconductor during the growth can be sufficiently eliminated, whereby the hydrogen is inactivated. The acceptor impurity that has been used can be sufficiently activated.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a case where the present invention is applied to the production of a p-type GaN layer will be described.

That is, the p-type Ga according to this embodiment is
In the method of preparing a N layer, firstly, put the c-plane sapphire substrate in a reaction furnace of the MOCVD apparatus, for example, mixed gas of 8l / min flow rate of H ₂ gas and e.g. 8l / min of the flow rate of N ₂ gas , The surface of the c-plane sapphire substrate is cleaned by performing a heat treatment at, for example, 1050 ° C. for 20 minutes.

Next, after the substrate temperature is lowered to, for example, 520 ° C., as shown in FIG. 1A, for example, the thickness 2 is deposited on the c-plane sapphire substrate 1 whose surface has been cleaned as described above.
MOCVD of 5 nm undoped GaN buffer layer 2
Grow by the method.

Next, after raising the substrate temperature to, for example, 1000 ° C., as shown in FIG.
A p-type GaN layer 3 having a thickness of, for example, 2 μm is grown thereon by MOCVD.

The GaN buffer layer 2 and the p-type G
In growing the aN layer 3, trimethyl gallium (TMG) is used as a Ga source, and ammonia (N
H ₃ ), and cyclopentadienyl magnesium (Cp ₂ Mg) is used as a p-type dopant. Further, as a carrier gas at the time of growth, H ₂ gas at a flow rate of 8 l / min and 8 l
A mixed gas with a flow rate of N ₂ gas per minute is used. The flow rates of the source gas and the p-type dopant gas are, for example, T
MG 40 μ-mol / min, ammonia 0.4 mol
/ Min, Cp ₂ Mg is about 40 μ-mol / min. Further, the growth pressure is, for example, 250 Torr.

The Mg concentration in the Mg-doped p-type GaN layer 3 grown in this manner was determined by secondary ion mass spectrometry (SIM).
It was 9 × 10 ¹⁹ cm ⁻³ when analyzed by the S) method. Further, the p-type GaN layer 3 immediately after the growth had a high resistance because the carrier concentration could not be measured by Hall measurement.

Next, as shown in FIG. 1C, the c-plane sapphire substrate 1 on which the p-type GaN layer 3 has been grown as described above.
With nitrogen (N ₂ ) gas and trimethylamine (N (CH ₃ )
The Mg in the p-type GaN layer 3 is activated by performing a heat treatment in a mixed gas atmosphere with the gas of ₃ ).

FIG. 2 shows a heat treatment apparatus used for this heat treatment. As shown in FIG. 2, in this heat treatment apparatus, a quartz tube 12 is provided in a heating furnace 11 using an infrared lamp. A carbon susceptor 13 is placed in the quartz tube 12, and a substrate 14 to be subjected to a heat treatment is placed on the carbon susceptor 13. In order to perform heat treatment using the heat treatment apparatus shown in FIG. 2, the c-plane sapphire substrate 1 on which the p-type GaN layer 3 has been grown is placed on the carbon susceptor 13 and the carbon susceptor 13 is
2, N ₂ gas is supplied into the quartz tube 12 at a rate of 2 l / l.
Flow rate of trimethylamine (N (CH ₃ ) ₃ )
While flowing at a flow rate of 0 ml / min, the c-plane sapphire substrate 1 is rapidly heated in the heating furnace 11 by infrared irradiation with an infrared lamp. Here, trimethylamine has a vapor pressure of about 1 atm at 0 ° C. Here, the trimethylamine was filled in a cylinder, the temperature of the cylinder was heated to 40 ° C., and the supply was controlled using a flow controller. .

FIGS. 3 and 4 show changes in the resistivity and hole concentration of the p-type GaN layer 3 when the heat treatment temperature is fixed at 1000 ° C. and the heat treatment time is changed from 1 minute to 100 minutes, respectively. . As is clear from FIGS. 3 and 4, both the resistivity and the hole concentration are remarkably improved by increasing the heat treatment time. When the heat treatment time is 100 minutes, the hole concentration is about 5 × 10 ¹⁸ cm ⁻³ and the resistivity is 0.2-0.3Ω
cm.

The reason why the hole concentration of the p-type GaN layer 3 increases as described above is that, because trimethylamine is contained in the atmosphere during the heat treatment, deterioration of the crystal of the p-type GaN layer 3 due to desorption of N is caused. This is considered to be due to the fact that hydrogen taken into the crystal was sufficiently eliminated at the same time. In this case, this trimethylamine is decomposed on the surface of the p-type GaN layer 3 to generate active nitrogen, which is converted into p-type GaN.
It is considered that the evaporation of N on the crystal surface of the layer 3 was prevented.

On the other hand, for comparison, the change in resistivity according to the heat treatment temperature, the change in resistivity according to the heat treatment time, and the change in hole concentration according to the heat treatment time of the p-type GaN layer 3 subjected to the heat treatment by the conventional method are respectively shown. These are shown in FIG. 5, FIG. 6 and FIG.

That is, FIG. 5 shows that the heat treatment temperature is 800 to 1
The change of the resistivity of the p-type GaN layer 3 depending on the heat treatment temperature when the heat treatment is performed for 3 minutes and 10 minutes while changing in the range of 100 ° C. is shown. As is clear from FIG. 5, when the heat treatment temperature is 800 to 900 ° C., the resistivity decreases to about 10 Ωcm, but when the heat treatment temperature is higher, the resistivity increases conversely. When the heat treatment temperature is 1000 ° C. or higher, the resistivity increases more remarkably for 10 minutes than for 3 minutes.

FIG. 6 shows the change in resistivity of the p-type GaN layer 3 when the heat treatment temperature is fixed at 1000 ° C. and the heat treatment is performed for 1, 3, and 10 minutes. As can be seen from FIG. 6, when the heat treatment temperature is 1000 ° C., even when the heat treatment time is one minute, the resistivity is as large as 9 Ωcm, and it can be seen that deterioration has already started.

FIG. 7 shows the change in the hole concentration of the p-type GaN layer 3 with the heat treatment time. As is clear from FIG. 7, the hole concentration decreases as the heat treatment time increases, and the optimum heat treatment time when the heat treatment temperature is 1000 ° C. is 1 minute or less.

As described above, according to this embodiment,
The heat treatment for activating Mg in the Mg-doped p-type GaN layer 3 is performed by using N ₂ gas and trimethylamine (N (CH ₃ )).
₃ ), the hole concentration is about 5 × 10 ¹⁸ cm ⁻³ , for example.
The p-type GaN layer 3 having an extremely high carrier concentration and a low resistivity as compared with the related art having a resistivity of about 0.2 Ωcm can be obtained.

The p-type GaN layer 3 is suitable for use as, for example, a contact layer of a p-side electrode in a GaN-based semiconductor laser, and has a contact resistance of 10 ^-3.
It can be reduced to 〜１０10 ⁻⁴ Ωcm ² . As a result, a lower operating voltage and a longer life of the semiconductor laser can be achieved.

As described above, one embodiment of the present invention has been specifically described. However, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible. .

For example, the numerical values given in the above-described embodiment are merely examples, and different numerical values may be used as needed. Further, in the above-described embodiment, ammonia (NH ₃ ) is used as an N material for growing the p-type GaN layer 3. The N material includes various nitrogen-containing hydrocarbons described above. For example, trimethylamine ((CH ₃ ) ₃ N) may be used.

[0046]

As described above, according to the heat treatment method for a nitride-based compound semiconductor according to the present invention, the nitride-based compound semiconductor is heat-treated in an atmosphere containing a nitrogen-containing hydrocarbon which does not release hydrogen during the nitrogen release process. By doing so, it is possible to perform heat treatment at a higher temperature for a longer time. For this reason, the hydrogen taken in the crystal of the nitride-based compound semiconductor during the growth can be sufficiently eliminated, and the acceptor impurity that has been inactivated by the hydrogen can be sufficiently activated. by this,
A p-type nitride-based compound semiconductor having a higher carrier concentration than conventional can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a method for manufacturing a p-type GaN layer according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a heat treatment apparatus used for heat treatment for activating impurities in a method for manufacturing a p-type GaN layer according to an embodiment of the present invention.

FIG. 3 is a schematic diagram showing a relationship between a heat treatment time and a resistivity of a p-type GaN layer when a heat treatment for activating impurities is performed in the method for manufacturing a p-type GaN layer according to one embodiment of the present invention; It is.

FIG. 4 shows a heat treatment for activating impurities in the method of manufacturing a p-type GaN layer according to one embodiment of the present invention.
FIG. 9 is a schematic diagram illustrating a relationship between a heat treatment time and a hole concentration of a p-type GaN layer when the heat treatment is performed at 000 ° C.

FIG. 5 is a schematic diagram illustrating a relationship between a heat treatment temperature and a resistivity of a p-type GaN layer when a heat treatment for activating impurities is performed by a conventional method.

FIG. 6 shows heat treatment time and p-type GaN when heat treatment for activating impurities is performed at 1000 ° C. by a conventional method.
FIG. 4 is a schematic diagram illustrating a relationship with a layer resistivity.

FIG. 7 shows heat treatment time and p-type GaN when heat treatment for activating impurities is performed at 1000 ° C. by a conventional method.
FIG. 4 is a schematic diagram illustrating a relationship with a hole concentration of a layer.

[Explanation of symbols]

1 ... c-plane sapphire substrate, 2 ... GaN buffer layer, 3 ... p-type GaN layer

Claims (8)

[Claims] 1. A method for heat-treating a nitride-based compound semiconductor in which an acceptor impurity is activated by heat-treating a nitride-based compound semiconductor doped with an acceptor impurity, the method comprising: A heat treatment method for a nitride-based compound semiconductor, wherein the heat treatment is performed on the nitride-based compound semiconductor in an atmosphere containing hydrocarbons. 2. The heat treatment method for a nitride-based compound semiconductor according to claim 1, wherein said nitride-based compound semiconductor is heat-treated in an atmosphere comprising an inert gas and said nitrogen-containing hydrocarbon. . 3. The nitrogen-containing hydrocarbon includes a hydro group bonded to nitrogen and an alkyl group and / or a phenyl group, and the number of the hydro groups is equal to the number of the alkyl group and the number of the phenyl group. 2. The heat treatment method for a nitride-based compound semiconductor according to claim 1, wherein the sum is not more than the sum of the numbers. 4. The method according to claim 3, wherein the nitrogen-containing hydrocarbon is an amine compound, an azo compound, a hydrazine compound or an azide compound. 5. The method according to claim 3, wherein the nitrogen-containing hydrocarbon is trimethylamine, dimethylamine, triethylamine or diethylamine. 6. The nitride-based compound semiconductor is Al, Ga
At least one kind of I selected from the group consisting of
2. The heat treatment method for a nitride-based compound semiconductor according to claim 1, comprising a group II element and N. 7. The heat treatment method for a nitride-based compound semiconductor according to claim 1, wherein a group II element is used as said acceptor impurity. 8. The heat treatment method for a nitride-based compound semiconductor according to claim 1, wherein said nitride-based compound semiconductor is grown by vapor phase metalorganic chemical vapor deposition.