JP2001094149A - P-type group iii nitride semiconductor and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for increasing carrier injection efficiency and for reducing a resistance, related to a p-type group III nitride semiconductor. SOLUTION: A GaN semiconductor is grown on a buffer layer provided on a substrate by an organic metal compound vapor-phase growth method using at least the gas of gallium source, a gas of nitrogen source, and a gas containing p-type impurity as a material gas. Here, a gas containing Mg is used as a gas containing p-type impurity, and a nitrogen gas is substantially used as a carrier gas for the material. For the amount of gas of indium source, the mole ratio of indium source gas is set at 0.001 to 1 of a gallium source gas, while the growth temperature is such temperature as the positive hole carrier concentration is 1×1017 cm-3 or above when it is measured at a room temperature, in a range 950-1,050 deg.C. Thus Al1-x-vGayInxN (wherein, 0<=y<1, x is a mole ratio corresponding to 1×1017 to 5×1020 cm-3, 0<x+y<=1) film, where Mg containing In by 1×1017 to 5×1020 cm-3 is doped is formed, to increase the positive hole carrier concentration without annealing.

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 (indium) gallium nitride-based compound semiconductor used for a blue light emitting diode, a blue laser diode or the like by metal organic compound vapor deposition (MOVPE).

[0002]

2. Description of the Related Art Conventionally, GaN has been used as a semiconductor material for blue light emitting diodes, blue laser diodes, and the like.
Attention has been focused on compound semiconductors such as AlGaN-based, GaInN-based, and the like. The GaN single crystal thin film is usually formed by MOVPE, in which, for example, an organic metal such as trimethylgallium (TMG), trimethylaluminum (TMA), or ammonia is supplied as a carrier gas using a hydrogen gas as a carrier gas and epitaxially grown on a sapphire substrate. can get. When AlGaN, GaN, or the like is formed by the MOVPE method, a method of adding Mg and Zn as acceptor impurities that form a light emission center in a short wavelength region is also known.

However, sapphire and GaN of the substrate have a large lattice constant mismatch and a large difference in thermal expansion coefficient, and when a GaN film is grown directly on the sapphire substrate, pits in the grown film, cracks at the interface between the grown film and the substrate, and the like. In addition to the macro defects described above, there are problems such as spatial micro fluctuations in the crystal orientation.
It is not easy to produce a high quality GaN single crystal thin film with a flat surface.

[0004] The present inventors have previously proposed a substrate temperature of 850-1.
It has been found that the above problem can be solved by depositing AlN on a sapphire substrate at a low temperature of about 600 ° C. immediately before the growth of the GaN film at 030 ° C. and using this as a buffer layer.
According to this method, the free electron concentration at room temperature is as low as about 10 ¹⁷ cm ^−3, which is about two orders of magnitude lower than when no AlN buffer layer is used, and the hole electron mobility at room temperature is 350 to 4
50 cm ² / V · s, which is about an order of magnitude larger. Further, by further developing this method, a film grown by doping with Mg which is an acceptor impurity has high resistance as it is,
It has been reported that the low-acceleration electron beam irradiation treatment results in a p-type, low resistance (several Ωcm), and improved light emission characteristics ("Japanese Journal OF Applied Physics" Vol.
28, L2112, 1989).

It is also known that GaN is used as a buffer layer. In addition to electron beam irradiation, low-resistance p-type gallium nitride is formed by heating at 400 ° C. or more in a nitrogen atmosphere and annealing. (Japanese Unexamined Patent Publication No. 5-18)
No. 3189) is also known.

[0006] By the additional steps after the crystal growth as described above, a low-resistance p-type GaN-based semiconductor can be obtained.
In order to obtain a low-resistance p-type GaN-based semiconductor by the MOVPE method itself, the general formula In _x Ga _1-xy N (0 <x <
After growing a semiconductor represented by 1,0 ≦ y <1), a method of growing GaN doped with Mg in a range of 1 × 10 ¹⁷ cm ^{−3 to} 3 × 10 ²⁰ cm ⁻³ ( JP-A-6-2
No. 32451), or when a GaN-based compound semiconductor doped with a p-type impurity such as Mg or Zn is crystal-grown at 1000 ° C. and cooled, the supply of ammonia is stopped in a temperature range of 600 ° C. or higher, and hydrogen or nitrogen is stopped. Method of obtaining a low-resistance p-type GaN-based compound semiconductor without heat treatment without causing hydrogen passivation in an atmosphere (Japanese Patent Laid-Open No. 8-1)
No. 15880), although hydrogen is used as a carrier gas for Cp ₂ Mg, TMG and TMA, in the growth process of the p-type conductive layer, nitrogen is used as a main carrier gas to prevent inactivation of Mg and to prevent growth after the growth. (Japanese Unexamined Patent Publication No. 10-135575) and the like are known.

A GaInN-based semiconductor is a material having a high light efficiency and emitting blue and green light. In particular, a material containing 10% or more of InN in a mixed crystal ratio in a visible region depends on the InN mixed crystal ratio. Since the emission wavelength can be adjusted, it is attracting attention as being important for display applications.
When growing InN, the growth temperature is 500-800.
The crystallinity is inferior to GaN because it is restricted by ° C. This is because while the melting point of GaN is about 1000 ° C.,
Since nN is about 500 ° C., when GaInN is grown at a high temperature of 600 ° C. or higher, GaInN is almost decomposed, and when it exceeds 800 ° C., In atoms evaporate.

Therefore, although there is a problem in that the characteristics such as the luminance of the light emitting element are lowered and the productivity is low, the growth is suspended once after the layer containing no In is grown, and the temperature of the substrate is reduced by 70%.
After the temperature is reduced to 0 to 900 ° C., the growth of the layer containing In is restarted, or the molar ratio of In in the source gas is increased, and
Method of setting the growth temperature to 0 to 900 ° C. (Japanese Patent Laid-Open No. 6-209)
121 publication).

[0009]

As a material that enables high-density recording media and full-color devices, Group III nitrides are promising. However, in order to drive this device with electric current, a pn junction must be formed. It is essential to take. In the MOVPE method used for producing a p-type GaN layer in each layer constituting a short-wavelength laser diode, for example, trimethylgallium and ammonia are used as GaN raw materials, and an impurity raw material of a p-type conductivity control material is used. As biscyclopentadienyl magnesium (Cp ₂ M
g) is used. Hydrogen is used as a carrier gas, the film growth temperature is around 1000 ° C., and Mg is G
By subsequently heat-treating the film doped in aN, a p-type low-resistance film is obtained.

However, in the conventional MOVPE method, GaN
, The p-type carrier concentration is at most 2 × 10 ¹⁸ cm ⁻³
In the case of GaInN, 5 × 10 ¹⁷ cm ⁻³
This is not sufficient in terms of increasing the efficiency of carrier injection and reducing the resistance. Therefore, now p-type G
It is particularly desirable to improve their properties by increasing the hole carrier concentration in the aN layer.

[0011]

The present inventors have made an invention relating to a new method as a method for increasing the carrier concentration, and have previously filed a patent application. That is, the present invention provides a method for forming a GaN-based semiconductor on a buffer layer provided on a substrate by using a gas containing at least a gallium source gas, a nitrogen source gas, and a p-type impurity as a source gas by metalorganic compound vapor deposition. In the growth method, a gas containing Mg is used as a gas containing a p-type impurity, a nitrogen gas is used substantially as a carrier gas for these raw materials, and a gas of an indium source is added, and the growth temperature is in the range of 800 to 1100 ° C. As a high-resistance Al _x Ga _1-xy in which Mg is inactivated
In _y N (where 0 ≦ x ≦ 1, 0 <y <0.3, x +
y <3) p-type II, characterized in that a film is formed and the hole carrier concentration is increased by annealing the film.
This is a method for producing a group I nitride semiconductor.

The present inventor further researched and developed that the Al _x Ga _{1 -xy} In _y N film was grown under a specific growth condition so that the hole carrier concentration could be increased without taking an annealing step. Can be increased. That is, the present invention provides 1 × 10 ^{17 to} 5 × 10 ²⁰
Al doped with Mg containing In of cm ^-3 _1-xy Ga _y
In _x N (where 0 ≦ y <1, x is 1 × 10 ^{17 to} 5 ×
0 <x + y ≦ 1) film having a mole fraction corresponding to 10 ²⁰ cm ⁻³ , wherein the hole carrier concentration measured at room temperature without annealing is 1 × 10 ¹⁷ cm ⁻³ or more. Is a p-type group III nitride semiconductor.

Further, according to the present invention, a GaN layer is formed on a buffer layer provided on a substrate by using a gas containing at least a gallium source gas, a nitrogen source gas, and a gas containing a p-type impurity as a source gas by metalorganic compound vapor phase epitaxy. In the method of growing a system-based semiconductor, a gas containing Mg is used as a gas containing a p-type impurity, a substantially nitrogen gas is used as a carrier gas for these raw materials, and the molar ratio of the indium source gas to the indium source gas is 0.0 for gallium source gas 1
And the growth temperature is set to 950 to 1
The hole carrier concentration is increased without taking an annealing step by setting the temperature to obtain a hole carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or more at room temperature in the range of 050 ° C. This is a method for producing a p-type group III nitride semiconductor.

According to the present invention, a high hole carrier concentration measured at room temperature of not less than 1.0 × 10 ¹⁷ cm ^-3 , more preferably not less than about 5.0 × 10 ¹⁷ cm ^-3. Was obtained, and the characteristics of increasing the efficiency of the light emitting diode and lowering the threshold value of the laser diode were realized.

The Mg to be doped needs to be about 1 × 10 ¹⁹ cm ⁻³ or more, and the Mg concentration is proportional to the flow rate of the gas containing Mg in a certain flow rate range. Adjust to

Trimethyl indium or triethyl indium added as a raw material of In has a high vapor pressure. Generally, unless the growth temperature is set to a low temperature of 800 ° C. or less, In is incorporated into GaN to such an extent that a mixed crystal is formed. In general, the growth temperature must be 800 ° C. or lower unless G
No mixed crystal phase of aInN appears.

As described above, when doping Mg as a p-type impurity element using a gas containing Mg as a gas containing a p-type impurity, substantially using nitrogen as a carrier gas and simultaneously supplying an indium compound Thus, GaInN formed at a growth temperature under a high temperature of 950 to 1050 ° C. is different from mixed crystal in that In is dissolved and GaN formed without supplying an indium compound at the same time using a carrier gas as a nitrogen gas. There is a large difference in hole carrier concentration as compared with a film or a GaInN mixed crystal film formed by simultaneously supplying an indium compound using a carrier gas as a hydrogen gas.

That is, a high hole carrier concentration cannot be obtained even if either the carrier gas as the raw material is substantially changed to the nitrogen gas or the indium compound is simultaneously supplied. The carrier gas may be substantially a nitrogen gas, and other gases such as a hydrogen gas may be mixed to some extent.

In the method of the present invention, by substantially using nitrogen gas as the carrier gas, the growth temperature, which was impossible when hydrogen was used as the carrier gas, was 950 ° C. to 950 ° C.
At a high temperature of 1050 ° C., an In-doped GaN layer having good crystallinity can be formed, and a high hole carrier concentration can be obtained.

However, the molar ratio of the indium source gas to the gallium source gas is 0.0
And the growth temperature is set to 950 to 1
In the range of 050 ° C., by increasing the growth temperature as the gas flow rate of the indium source is increased, the result of SIMS analysis shows that the I 10 of 10 ¹⁷ to 10 ²⁰ cm ⁻³ with respect to the volume of the grown film.
A GaN film containing n is formed. In this case, a hole carrier concentration of 1.0 × 10 ¹⁷ cm ⁻³ or more can be obtained without as-grown, ie, without performing an annealing step.

Japanese Patent Application Laid-Open No. 8-115880 discloses that when ammonia is used as a nitrogen source, the cooling atmosphere is changed from ammonia to hydrogen in order to avoid the supply of atomic hydrogen supplied from ammonia after the growth is completed. Alternatively, switching to a mixed atmosphere of nitrogen is indispensable for obtaining a low-resistance p-type GaN compound semiconductor without causing hydrogen passivation. However, according to the method of the present invention, the supply of ammonia is stopped after the growth is completed. Feasible without the need.

The reason why hydrogen is used as a carrier gas in the conventional MOVPE method is that hydrogen is easily purified and the gas flow is not easily disturbed. This is because a film having good crystallinity cannot be formed due to poor decomposition efficiency and poor diffusion in a carrier gas. In this experiment, nitrogen was used as a carrier gas, because it does not contribute much to the reaction during nitride crystal growth as compared with hydrogen. Therefore, the same effect can be expected even if an inert gas other than nitrogen, for example, an argon gas or a helium gas is used instead of the nitrogen gas.

The reason why a high hole carrier concentration can be obtained under the above-mentioned conditions of the present invention is not fully understood, but by using a nitrogen gas as the carrier gas, the use of a hydrogen gas as a carrier gas can be improved. In a state in which the occurrence of hydrogen passivation is reduced, that is, when the growth temperature is high and NH
Hydrogen atoms decomposed from the ₃ gas are taken into the crystal to some extent together with Mg to prevent the activation of Mg, but in this state, 10 ¹⁷ to 10 10
^{When a 20} cm ^-3 In-added GaN layer is formed, M
It is considered that the activation effect of g is remarkably exhibited.

The molar ratio of the In source gas supplied as a source gas during the growth was 0.00
It is adjusted to 1 or more, more preferably 0.01 or more, but 1.0 or less. If it is less than 0.001, the solvent G
The effect of In as a solute incorporated in aN or AlGaN is small, and is not effective in activating Mg. 1
If it is larger, the increase in dislocations in GaN or AlGaN cannot be suppressed.
Hinders activation. It is preferable to increase the molar ratio of the In source gas as the growth temperature increases, and accordingly the crystallinity improves. The amount of In addition mainly varies depending on the molar ratio of In and the growth temperature.

[0025] was in the range of the growth temperature 950 to 1050 ° C., although elevated temperatures as the crystallinity of the GaN is good, for the formation of _{Al 1-xy Ga y In x} N of In addition may lower temperature, this In this range satisfying both conditions, I having good crystallinity
This is because an n-added GaN layer is obtained.

To form GaN by the MOVPE method, ammonia is usually used as a reaction gas of a nitrogen source.
In this case, in order to deposit a compound semiconductor having few crystal defects on a substrate at a practical rate, an ammonia flow rate of 500,000 times that of an alkyl compound of a group III element is required. Although the efficiency can be increased, the present invention can be grown at a high temperature close to this temperature, and has an effect of increasing the efficiency of using ammonia and significantly improving the productivity.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method of the present invention, a conventionally known apparatus for growing GaN on sapphire of a substrate using a horizontal reaction tube can be used. For example, the substrate holder to be induction-heated is placed in a horizontal tubular reaction tube, the sapphire substrate is held diagonally in the holder, and the reaction gas flows into the reaction tube together with the carrier gas at normal pressure from the introduction port into the reaction tube. After the decomposition and the deposition of the compound semiconductor film on the substrate, the reaction gas is discharged from the vacuum exhaust port.
The growth temperature can be controlled by adjusting the temperature of the carbon susceptor by the current flowing through the RF coil. Temperature measurement may use a thermocouple.

As the substrate, Si, SiC, sapphire or the like can be used. On the substrate, at low temperature, AlN, Ga
N, formula _{Ga s Al t N (s +} t = 1,0 <s <1,
A compound semiconductor represented by 0 <t <1) or a stacked structure thereof is provided as a buffer layer by a known means.

As a raw material of GaN, typically,
Methyl gallium (TMG) and / or triethyl gallium
Trialkyl gallium such as lithium (TEGa), ammonia
Near (NH_Three), And biscyclopenta
Dienyl magnesium (Cp _TwoMg).

Instead of ammonia as a nitrogen source, N
_TwoH_Four, (CH_Three) CNH_Two, C_TwoH_FiveN _Three, CH_ThreeN
H ・ NH_TwoMay be used.

As the Mg raw material, methyl biscyclopen
Tadienyl magnesium (C₆H₇)_TwoMg, (CH_Three
C_FiveH_Four)_TwoMg, (C_FiveH_FiveC_FiveH_Four)_TwoMg, (i
-C _ThreeH₇C_FiveH_Four)_TwoMg, (n-C_ThreeH₇C
_FiveH_Four)_TwoMg or the like may be used.

The raw materials for Al include trimethyl aluminum (TMAl) and triethyl aluminum (TEA).
As a raw material of trialkylaluminum and In such as l), trialkylindium such as trimethylindium (TMIn) and triethylindium (TEIn) is suitable.

As specific conditions, TMGa: 2.5 to
25 μmol / min, TMAl: 30 to 300 μmol /
Min, ammonia: 0.02 to 0.2 mol / min, biscyclopentadienyl magnesium (Cp ₂ Mg): 0.1
01-0.5 μmol / min, TMI: 1-100 scc
m, nitrogen as a carrier gas: 300 to 3000 sc
cm, a growth temperature of 950 to 1050 ° C., a growth pressure of 70 to 760 Torr, and a thickness of 100 to 20 Torr.
A 00 nm p-type AlGaInN layer is grown. The absolute flow rate of the gas can be controlled by voltage control using a mass flow controller. In order to express the flow rate ratio in terms of the ratio of the absolute amount of the substance, the amount of the substance is converted from the value of the mass flow controller, whereby the gas flow rate ratio can be obtained.

[0034]

Example 1 An atmospheric pressure MOVPE method using a horizontal reaction tube was carried out under the following conditions. A sapphire (0001) plane was used as the substrate.
After hydrogen baking at 50 ° C. for 10 minutes, an AlN buffer layer of about 50 nm was deposited at a growth temperature of 600 ° C. for a growth time of 5 minutes. The flow rate of the raw material is TMA: 5
sccm, NH ₃ : 1slm, N as carrier gas
₂ : Performed with a total amount of 3 slm.

Subsequently, GaN: Mg was deposited at a growth temperature of about 950 ° C. for a growth time of about 20 minutes to deposit a GaN layer of about 2 μm. The flow rate is TMG: 20 sccm, Cp ₂ Mg: 1
The process was performed at 50 sccm, NH ₃ : 1 slm, and N ₂ as a carrier gas: a total amount of ₃ slm, and the supply of ammonia was continued even after the film growth was completed. TMI flow rate is 10, 15s
ccm, the amount of In added to the obtained GaInN film is about 1.1 × 10 ¹⁹ cm ⁻³ , and the Mg concentration is 2 × 10 ¹⁹ c
At m ^-3 , the mobility was 0.44 cm ² / VS. As shown in Table 1 and FIG.
Hole carrier concentration of about 5.0 × 10 ¹⁷ cm ⁻³ between ccm
The above p-type GaInN film was obtained.

[0036]

[Table 1]

Example 2 The growth temperature was 1000 ° C., and other conditions were the same as in Example 1. TMI flow rate of 35, 40, 45 sccm
In this case, the amount of In added to the obtained GaInN film is about 5.0 × 10 ¹⁹ cm ⁻³ and the Mg concentration is 2 × 10 ¹⁹ cm 3.
^-3 , and the mobility was 0.50 cm ² / VS. As shown in Table 1 and FIG. 1, the TMI flow rate is 30 to 70 sc.
Thus, a p-type GaInN film having a hole carrier concentration of about 5.0 × 10 ¹⁷ cm ⁻³ or more was obtained.

Example 3 The growth temperature was 1050 ° C., and the other conditions were the same as in Example 1. TMI flow rate of 70, 73, 75, 80s
ccm, the amount of In added to the obtained GaInN film is about 5.6 × 10 ¹⁹ cm ⁻³ , and the Mg concentration is 2 × 10 ¹⁹ c
At m ^-3 , the mobility was 0.39 cm ² / VS. As shown in Table 1 and FIG.
Hole carrier concentration of about 5.0 × 10 ¹⁷ cm ⁻³ between ccm
The above p-type GaInN film was obtained.

[0039]

According to the present invention, the carrier injection efficiency can be increased by using the electrodes indispensable for the current driving operation of devices such as light emitting diodes and laser diodes.
As a result, a large effect is brought about for increasing the efficiency of the light emitting diode and lowering the threshold value of the laser diode.

[Brief description of the drawings]

FIG. 1 shows growth temperature, TM in Examples 1 to 3 of the present invention.
4 is a graph showing the relationship between I flow rate and hole carrier concentration.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA03 CA40 CA57 CA65 5F045 AA04 AB09 AB14 AB17 AB18 AC07 AC08 AC09 AC12 AC15 AD13 AD14 AE23 AE25 AE29 AF02 AF03 AF09 AF13 BB08 BB16 CA11 CA12 DA53 DA59 DP07 DQ06 EB15 FE5 CB05 CB07 CB19 DA05 EA23 EA24

Claims (2)

[Claims] 1. 1 × 10¹⁷~ 5 × 10²⁰cm^-3In
Containing Mg doped Al_1-xyGa_yIn_xN (just
And 0 ≦ y <1, x is 1 × 10¹⁷~ 5 × 10 ²⁰cm^-3To
Corresponding molar fraction, 0 <x + y ≦ 1)
Hole carrier concentration measured at room temperature without cooling
1 × 10¹⁷cm^-3P-type III
Group nitride semiconductor. 2. A GaN-based semiconductor is grown on a buffer layer provided on a substrate by organometallic compound vapor deposition using at least a gallium source gas, a nitrogen source gas, and a gas containing a p-type impurity as source gases. In this method, a gas containing Mg is used as a gas containing a p-type impurity, a substantially nitrogen gas is used as a carrier gas for these raw materials, and the molar ratio of the indium source gas is 1 gallium source gas. And a hole carrier concentration of 1 × 10 ¹⁷ c measured at room temperature in a range of 950 to 1050 ° C.
2. The method for producing a p-type group III nitride semiconductor according to claim 1, wherein the hole carrier concentration is increased without taking an annealing step by setting the temperature to obtain a temperature not lower than m ^-3 .