JP3298454B2 - Method of manufacturing gallium nitride based compound semiconductor light emitting device - Google Patents

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 compound semiconductor light emitting device used for a light emitting device such as an ultraviolet or blue light emitting laser diode, or an ultraviolet or blue light emitting diode.
The present invention relates to a method for manufacturing a child .

[0002]

2. Description of the Related Art A blue light emitting device is a ZnS of II-VI group.
e, studies have been carried out using SiC of the IV-IV group, GaN of the III-V group and the like, and recently, among them, a gallium nitride-based compound semiconductor [In _x Al _Y Ga _{1-x -Y} N (0 ≦
X, 0 ≦ Y, X + Y ≦ 1)] have been reported to exhibit relatively excellent light emission at room temperature, and have attracted attention. Blue light emitting device having the nitride semiconductor is essentially the formula on a substrate made of sapphire _{In X Al Y Ga 1-X} -Y N
It has a structure in which epitaxial layers of a nitride semiconductor represented by (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) are sequentially stacked in n-type and i-type or p-type.

As a method of laminating a nitride semiconductor, a metal organic compound vapor deposition method (hereinafter referred to as MOCVD method),
Vapor phase growth methods such as molecular beam epitaxy (hereinafter referred to as MBE) are well known. For example, the method using the MOCVD method will be briefly described. In this method, an organometallic compound gas such as trimethylgallium (TMG), trimethylaluminum (TMA), ammonia or the like is used as a reaction gas in a reaction vessel provided with a sapphire substrate. Is supplied, the crystal growth temperature is maintained at a high temperature of about 900 ° C. to 1100 ° C., and the nitride semiconductor is grown on the substrate. , I-type, or p-type.
In addition to sapphire, the substrate may be SiC, Si, or the like, but sapphire is generally used. Well-known n-type impurities are Si, Ge, and Sn (however, in the case of a nitride semiconductor, they have a property of becoming n-type without doping with an n-type impurity). Cd, B
e, Mg, Ca, Ba and the like.
g and Zn are best known.

Further, as one method of forming a nitride semiconductor by the MOCVD method, if a nitride semiconductor is grown directly on a sapphire substrate at a high temperature, the surface state and crystallinity are significantly deteriorated. Before you do,
Forming a buffer layer made of AlN at a low temperature of about 0 ° C.,
Subsequently, it has been revealed that the crystallinity is remarkably improved by performing growth at a high temperature on the buffer layer (Japanese Patent Application Laid-Open No. 2-229476). In addition, the present inventor has shown in Japanese Patent Application No. 3-89840 that a crystalline nitride semiconductor having better crystallinity can be laminated using GaN as a buffer layer than the conventional method using AlN as a buffer layer.

However, a blue light emitting device having a nitride semiconductor has not yet been put to practical use. This is because a nitride semiconductor cannot be made into a p-type with low resistance, so that a light-emitting element having various structures such as a double hetero structure and a single hetero structure cannot be formed. Even if a nitride semiconductor doped with a p-type impurity is grown by a vapor phase growth method, the obtained nitride semiconductor does not become a p-type and a high-resistance semi-insulating material having a resistivity of 10 ⁸ Ω · cm or more. That is, it was the actual situation that it became i-type. For this reason, at present, only the so-called MIS structure of a blue light emitting element is known, in which a buffer layer, an n-type layer, and an i-type layer are sequentially stacked on a substrate.

[0006]

As means for lowering the resistance of a high-resistance i-type so as to approach the p-type, Japanese Patent Laid-Open No. 2-25 / 1990
No. 7679, a high-resistance i-type gallium nitride compound semiconductor doped with Mg as a p-type impurity is formed in the uppermost layer, and then the surface is irradiated with an electron beam having an accelerating voltage of 6 kV to 30 kV so that about 0.5 μm
A technique for reducing the resistance of a layer has been disclosed. However, this method has a problem that only the penetration depth of the electron beam, that is, the resistance can be reduced only on the very surface, and the entire wafer must be irradiated while scanning the electron beam, so that the resistance cannot be reduced uniformly in the plane. there were.

Therefore, an object of the present invention is to make a nitride semiconductor doped with a p-type impurity a low-resistance p-type, furthermore, the resistance value is uniform over the entire wafer regardless of the film thickness, and the light-emitting element can be a double heterostructure. An object of the present invention is to provide a method for manufacturing a nitride semiconductor light emitting device having a pn junction which can have a structure capable of a single hetero structure.

[0008]

Means for Solving the Problems] In the method of the present invention are prepared
The gallium nitride-based compound semiconductor includes a gallium nitride-based compound semiconductor layer containing silicon and a gallium nitride-based compound semiconductor layer containing magnesium. Further, the gallium nitride-based compound semiconductor of the present invention, on the gallium nitride-based compound semiconductor layer containing magnesium, suppresses decomposition of the gallium nitride-based compound semiconductor, and removes magnesium in the gallium nitride-based compound semiconductor layer containing magnesium. While passing at least a portion of the bound hydrogen,
In annealing, the gallium nitride-based compound semiconductor layer containing magnesium is uniformly p-planed and uniformly in the depth direction.
A cap layer to be formed is provided.

Annealing (annealing: heat treatment) may be performed in a reaction vessel after growing a gallium nitride-based compound semiconductor layer doped with a p-type impurity, or a wafer may be taken out of the reaction vessel and used exclusively for annealing. It may be performed by an apparatus. The annealing atmosphere is performed in a vacuum, in an atmosphere of an inert gas such as N ₂ , He, Ne, or Ar, or in a mixed gas atmosphere thereof. Preferably, nitrogen is pressurized at a temperature higher than the decomposition pressure of the gallium nitride-based compound semiconductor at the annealing temperature. Perform in an atmosphere. Because
This is because pressurization in a nitrogen atmosphere has an effect of preventing N in the gallium nitride-based compound semiconductor from decomposing and coming out during annealing.

For example, in the case of GaN, the decomposition pressure of GaN is 8
About 0.01 atm at 00 ° C, about 1 atm at 1000 ° C, 11
It is about 10 atmospheres at 00 ° C. Therefore, when annealing a gallium nitride-based compound semiconductor at 400 ° C. or higher,
More or less decomposition of the gallium nitride-based compound semiconductor occurs, and its crystallinity tends to deteriorate. Accordingly, decomposition can be prevented by pressurizing with nitrogen as described above.

The annealing temperature is, for example, 400 ° C.
The above is carried out at preferably 700 ° C. or more, for 1 minute or more, preferably for 10 minutes or more. Even at a temperature of 1000 ° C. or higher, decomposition can be prevented by pressurizing with nitrogen as described above, and as described later, a stable p-type gallium nitride-based compound semiconductor having excellent crystallinity can be obtained. .

As a means for suppressing the decomposition of the gallium nitride-based compound semiconductor during annealing, a cap layer is further formed on the gallium nitride-based compound semiconductor layer doped with a p-type impurity, and then annealing is performed. The cap layer is a protective film, which is formed on a gallium nitride-based compound semiconductor doped with a p-type impurity, and then annealed at 400 ° C. or more to reduce the pressure, not to mention the pressure. Even under normal pressure, the gallium nitride-based compound semiconductor can be made into a low-resistance p-type without decomposing.

In order to form a cap layer, a gallium nitride-based compound semiconductor layer doped with a p-type impurity may be formed and then formed in a reaction vessel, or a wafer may be taken out of the reaction vessel. It may be formed by another crystal growth apparatus such as a plasma CVD apparatus. As the material of the cap layer, any material can be used as long as it is a material that can be formed on the gallium nitride-based compound semiconductor and is stable at 400 ° C. or higher, and preferably Ga _x Al ₁ -XN.
(Where 0 ≦ X ≦ 1), Si ₃ N ₄ , and SiO ₂ can be given, and the type of material is appropriately selected depending on the annealing temperature. The thickness of the cap layer is usually 0.01 to 5 μm.
m. When the thickness is less than 0.01 μm, the effect as a protective film cannot be sufficiently obtained. When the thickness is more than 5 μm, it takes time to remove the cap layer by etching after annealing and expose the p-type gallium nitride-based compound semiconductor layer. This is not economical.

[0014]

FIG. 1 is a diagram showing that a gallium nitride-based compound semiconductor layer doped with a p-type impurity changes to a low-resistance p-type by annealing. However, this figure shows the MO
First, a GaN buffer layer is formed on a sapphire substrate using a CVD method, and a GaN layer is formed to a thickness of 4 μm while doping Mg as a p-type impurity thereon. Then, the wafer is taken out and the temperature is changed. FIG. 3 is a diagram in which holes are measured on a wafer after annealing is performed for 10 minutes in a nitrogen atmosphere, and resistivity is plotted as a function of annealing temperature.

As can be seen from this figure, when the annealing time is set to 10 minutes, the resistivity of the Mg-doped GaN layer sharply decreases from around 400 ° C.
It shows almost constant low-resistance P-type characteristics from 00 ° C.
The effect of annealing appears. The GaN layer not annealed and the Ga annealed at 700 ° C. or more
The hole measurement results of the N layer show that the GaN layer before annealing has a resistivity of 2 × 10 ⁵ Ω · cm and a hole carrier concentration of 8 × 1.
0 ¹⁰ / cm ³ , whereas G after annealing
The aN layer has a resistivity of 2Ω · cm and a hole carrier concentration of 2 × 1.
0 ¹⁷ / cm ³ .

Further, the 4 μm GaN layer annealed at 700 ° C. is etched to a thickness of 2 μm,
As a result of the hole measurement, a hole carrier concentration of 2 × 10
¹⁷ / cm ³ and resistivity ³ Ω · cm, almost the same values as before etching. That is, the GaN layer doped with the P-type impurity becomes low-resistance p-type uniformly in the depth direction over the entire region by annealing.

FIG. 2 shows a wafer obtained by forming a GaN buffer layer and a Mg-doped GaN layer of 4 μm on a sapphire substrate by MOCVD.
Annealing was performed for 20 minutes in a nitrogen atmosphere at 000 ° C., and the p-type GaN layers of the wafer (a) performed under a pressure of 20 atm and the wafer (b) performed at an atmospheric pressure were respectively subjected to H annealing.
FIG. 3 is a diagram illustrating irradiation with an e-Cd laser as an excitation light source, and comparison of crystallinity with photoluminescence intensity thereof.
The higher the blue luminescence intensity of the photoluminescence at 450 nm, the better the crystallinity can be evaluated.

As shown in FIG. 2, when annealing is performed at a high temperature of 1000 ° C. or higher, the crystallinity of the GaN layer tends to be deteriorated due to thermal decomposition. P-type G with excellent crystallinity
An aN layer is obtained.

FIG. 3 shows a wafer (c) in which a GaN buffer layer and a 4 μm Mg-doped GaN layer are formed on a sapphire substrate, and a 0.5 μm AlN layer as a cap layer thereon. The wafer (d) grown at a thick thickness is then subjected to a pressure of 1000
After annealing for 20 minutes in a nitrogen atmosphere at ℃
P exposed by removing the cap layer by etching
FIG. 4 is a diagram showing the crystallinity of a GaN layer in comparison with the photoluminescence intensity.

As shown in FIG. 3, the p-type GaN layer (c) that has been annealed without growing the cap layer is decomposed when the annealing is performed at a high temperature. Becomes weaker. However, by growing the cap layer (in this case, AlN), the AlN of the cap layer is decomposed but the p-type GaN layer is not decomposed, so that the emission intensity is still strong.

The reason why a low-resistance p-type gallium nitride-based compound semiconductor can be obtained by annealing is presumed to be as follows.

That is, in growing a gallium nitride-based compound semiconductor layer, NH ₃ is generally used as an N source, and it is considered that the NH ₃ is decomposed during growth to form atomic hydrogen. It is considered that this atomic hydrogen combines with Mg, Zn, or the like doped as an acceptor impurity to prevent p-type impurities, such as Mg or Zn, from functioning as an acceptor. For this reason, p
A gallium nitride-based compound semiconductor doped with a type impurity exhibits high resistance.

However, by performing annealing after growth, hydrogen bonded in the form of Mg—H, Zn—H, or the like is thermally dissociated, and the gallium nitride-based compound semiconductor layer doped with p-type impurities is removed. Since the p-type impurity comes out and functions normally as an acceptor, a low-resistance p-type impurity
A gallium nitride-based compound semiconductor can be obtained. Therefore, it is not preferable to use a gas containing a hydrogen atom such as NH ₃ or H ₂ in the annealing atmosphere. It is not preferable to use a material containing a hydrogen atom also in the cap layer for the above-described reason. Note that, in the present invention, the term “hydrogen removed from a gallium nitride-based compound semiconductor containing a p-type impurity” does not necessarily mean that all hydrogen is removed, but that part of hydrogen is removed. It goes without saying that it is within the range.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments.
However, in Reference Example 1 below, a light emitting device having no cap layer was used.
The manufacture of an optical device is illustrated.
The optical element is keyed by the method described in [0012] and [0013].
A cap layer can be provided. Reference Example 1 First, a well-cleaned sapphire substrate is set on a susceptor in a reaction vessel. After evacuating the container, the substrate is heated at 1050 ° C. for 20 minutes while flowing hydrogen gas to remove oxides on the surface. Thereafter, the temperature was cooled to 510 ° C., and at 510 ° C., TMG gas was
^3.10-6 mol / min, ammonia gas as N source
0 liter / min, hydrogen gas 2.0
While flowing at a rate of 1 liter / min, the GaN buffer
It is grown to a thickness of Å.

Next, only the TMG gas was stopped and the temperature was set at 103
After the temperature was raised to 0 ° C., TMG gas was
^-6 mol / min and a new SiH ₄ (monosilane) gas flowing at 2.2 × 10 ⁻¹⁰ mol / min for 60 minutes to grow the Si-doped n-type GaN layer to a thickness of 4 μm. grow up.

Subsequently, the SiH ₄ gas is stopped, and Cp ₂ Mg gas is grown at a flow ^rate of 3.6 × 10 ⁻⁶ mol / min for 30 minutes to grow the Mg-doped GaN layer to a thickness of 2.0 μm.

After stopping TMG gas and Cp ₂ Mg gas and cooling to room temperature while flowing hydrogen gas and ammonia gas, the gas flowing into the reaction vessel is replaced with nitrogen gas, and nitrogen gas is passed through the inside of the reaction vessel. The temperature is raised to 1000 ° C. and held in the reaction vessel for 20 minutes for annealing.

When the device thus obtained was used as a light emitting diode to emit light, it showed blue light emission having an emission peak near 430 nm, and the light emission output was 50 μm at 20 mA.
W, and the forward voltage was also 4 V at 20 mA. In addition, when a device having the same structure was produced without annealing and used as a light emitting diode, the light emitting device emitted a slightly yellow light at 20 mA, and the diode was immediately broken.

[0029]

The present invention realizes the following extremely excellent features.
Manifest. Until now, even if a p-type impurity is doped, a low resistance p
Gallium nitride based compounds that were extremely difficult to form as mold layers
The semiconductor layer is annealed to form a low resistance p-type gallium nitride.
System compound semiconductor. When annealing,
Gallium nitride based semiconductor containing Mg as a p-type impurity
Hydrogen removed from the body layer can be quickly removed. The present invention
Gallium nitride-based compound semiconductor light emitting device
Gallium nitride based compound semiconductor layer and p-type impurity Mg
Gallium nitride based compound semiconductor layer doped with
After that, it is very easy to anneal this
The layer containing Mg, which is a p-type impurity, is converted into a p-type
Gallium nitride based compound with excellent light emission characteristics at low cost
The feature is that a large number of semiconductor light emitting devices can be produced. The gallium nitride based compound semiconductor light emitting device of the present invention,
Gallium nitride based semiconductor containing Mg as a p-type impurity
There is a feature that the entire surface of the body layer can be uniformly and efficiently p-type.
Gallium nitride based semiconductor containing Mg as a p-type impurity
Annealing of the body layer is performed by uniformly heating the layer body to make it p-type.
Let Gallium nitride based compounds containing Mg as a p-type impurity
That the entire semiconductor layer can be made uniform p-type
This is extremely important when manufacturing wafers. So
This is because gallium nitride based compound semiconductor light emitting devices
A wafer is manufactured, cut into small pieces, and
Manufactures a chip of an element-based compound semiconductor light emitting device,
The gallium nitride-based compound semiconductor layer is uniformly p-type.
Otherwise, the yield of manufactured chips will drop significantly.
Because Gallium nitride based compound semiconductor layer containing p-type impurities
Are deeply p-typed and more uniformly p-typed as a whole.
And realizes excellent light emission characteristics. In contrast, p-type
A semiconductor layer containing impurities is made p-type with an electron beam
Conventional gallium nitride-based compound semiconductor light-emitting devices
The uppermost layer is a semiconductor layer containing a pure substance, and at the very surface
However, the resistance is reduced by making it p-type only. Accelerated electrons
This is because the beam cannot be driven deeply. Departure
Ming's gallium nitride based compound semiconductor light emitting deviceManufacturing method
Is a gallium nitride system containing Mg as a p-type impurity
The entire compound semiconductor layer is heated by annealing,
Gallium nitride containing p-type impurities
The entire compound semiconductor layer is heated to be more uniformly p-type.
As a result, a light emitting element with extremely high luminance can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between an annealing temperature and a resistivity according to an embodiment of the present invention.

FIG. 2 is a diagram showing the crystallinity of a p-type GaN layer according to one embodiment of the present invention in comparison with photoluminescence intensity.

FIG. 3 is a diagram showing the crystallinity of a p-type GaN layer according to one embodiment of the present invention in comparison with photoluminescence intensity.

Continuation of the front page (56) References JP-A-2-303064 (JP, A) JP-A-2-142188 (JP, A) JP-A-62-119196 (JP, A) JP-A-57-23284 (JP) JP-A-54-72589 (JP, A) JP-A-2-111016 (JP, A) JP-A-3-218625 (JP, A) JP-A-59-228776 (JP, A) U.S. Pat. (US, A) Applied Physics, Vol. 60, No. 2, p. 163-166 Inst. Phys. Conf. Ser. No 106 Chapter 8, p. 575-580 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 33/00 H01S 5/00-5/50 H01L 21/324 H01L 21/205

Claims (2)

(57) [Claims] An n-type gallium nitride-based compound semiconductor layer containing at least silicon and a gallium nitride-based compound semiconductor layer containing magnesium are grown on a substrate by a vapor phase growth method. The entire gallium nitride-based compound semiconductor layer and the gallium nitride-based compound semiconductor layer containing magnesium, in an atmosphere containing substantially no hydrogen,
A method for producing a gallium nitride-based compound semiconductor light-emitting device in which hydrogen is extracted from the gallium nitride-based compound semiconductor layer containing magnesium by annealing at 400 ° C. or more to form a p-type gallium nitride-based compound semiconductor layer, On the gallium nitride-based compound semiconductor layer containing magnesium, at the annealing, the decomposition of the gallium nitride-based compound semiconductor is suppressed, and at least a part of hydrogen dissociated from magnesium is suppressed from the gallium nitride-based compound semiconductor layer containing magnesium. Is provided, and a magnesium-containing gallium nitride-based compound semiconductor layer provided on the cap layer is annealed to form a low-resistance p-type gallium nitride-based compound semiconductor uniformly in the depth direction. gallium nitride-based compound semiconductor onset
A method for manufacturing an optical element . Material wherein said cap layer, _Ga X Al
_{2. The} method for producing a gallium nitride-based compound semiconductor according to claim 1, wherein the method is one selected from _1- XN (where 0 ≦ X ≦ 1), Si ₃ N ₄ , and SiO ₂ .