JP2540791B2 - A method for manufacturing a p-type gallium nitride-based compound semiconductor. - Google Patents

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 a p-type gallium nitride-based compound semiconductor used in a light emitting device such as an ultraviolet light emitting diode, a blue light emitting laser diode, an ultraviolet light emitting diode, and a blue light emitting diode. The present invention relates to a method of making a gallium nitride-based compound semiconductor layer formed by doping a p-type impurity into a p-type having a low resistance.

[0002]

2. Description of the Related Art A blue light emitting device is a ZnSe, I of II-VI group.
Studies have been conducted using V-IV group SiC, III-V group GaN, etc., and recently, gallium nitride compound semiconductors [Ga _X Al _1-X N (where 0 ≦ X ≦ 1)] It has been noticed that it exhibits relatively excellent light emission at room temperature.
The blue light emitting device having the gallium nitride compound semiconductor is basically a gallium nitride compound represented by the general formula Ga _X Al _{1 -X} N (where 0 ≦ X ≦ 1) on a substrate made of sapphire. The semiconductor epitaxial layer has a structure in which n-type and i-type or p-type semiconductor layers are sequentially stacked.

As a method for stacking gallium nitride-based compound semiconductors, metal-organic compound vapor phase epitaxy (hereinafter MOCVD) is used.
Called law. ), A molecular beam epitaxy method (hereinafter referred to as MBE method) and the like are well known. For example,
Briefly explaining the method using the MOCVD method,
In this method, an organometallic compound gas {trimethylgallium (TMG), trimethylaluminum (TMA), ammonia, etc.) is supplied as a reaction gas into a reaction vessel in which a sapphire substrate is installed, and the crystal growth temperature is about 900 ° C.
The gallium nitride-based compound semiconductor is grown at a high temperature of 1100 ° C. to grow the gallium nitride-based compound semiconductor on the substrate, and while supplying other impurity gas as necessary, the gallium nitride-based compound semiconductor is n-doped.
It is a method of laminating into a die, an i-type, or a p-type. In addition to sapphire, the substrate includes SiC, Si, etc., but sapphire is generally used. Si as the n-type impurity
(However, gallium nitride-based compound semiconductors have the property of becoming n-type even if they are not doped with n-type impurities.) As p-type impurities, Zn, Cd, Be,
Mg, Ca, Ba and the like can be mentioned. Among them, Mg,
Zn is best known.

When a gallium nitride-based compound semiconductor is grown directly on a sapphire substrate at a high temperature as one of the methods for forming a gallium nitride-based compound semiconductor by the MOCVD method, the surface condition and crystallinity of the gallium nitride-based compound semiconductor are significantly deteriorated. Before growing at a high temperature, first, at a low temperature around 600 ° C, AlN
It has been clarified that the crystallinity is remarkably improved by forming a buffer layer composed of the above and then growing it on the buffer layer at a high temperature (JP-A-2-22947).
No. 6). Further, the present inventor has shown in Japanese Patent Application No. 3-89840 that a crystalline gallium nitride-based compound semiconductor that is superior to GaN as a buffer layer can be stacked more than a conventional method using AlN as a buffer layer. It was

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

[0006]

As means for lowering the resistance of a high resistance i-type and making it closer to a p-type, Japanese Patent Laid-Open No. 2525/1990.
In Japanese Patent No. 7679, a high-resistance i-type gallium nitride compound semiconductor doped with Mg as a p-type impurity is formed on the uppermost layer, and then the surface is irradiated with an electron beam with an accelerating voltage of 6 kV to 30 kV. 0.5 μm
A technique for reducing the resistance of the layer is disclosed. However, in this method, only the penetration depth of the electron beam, that is, only the extreme surface can be lowered, and since the entire wafer must be irradiated while scanning the electron beam, there is a problem that the resistance cannot be uniformly lowered in the plane. there were.

Therefore, an object of the present invention is to use a p-type impurity-doped gallium nitride-based compound semiconductor as a p-type having a low resistance, and the resistance value is uniform over the entire wafer regardless of the film thickness. Provided is a method for manufacturing a p-type gallium nitride-based compound semiconductor capable of forming a structure capable of forming a terrorism or single hetero structure.

[0008]

A method of manufacturing a p-type gallium nitride compound semiconductor according to the present invention is a method for producing a p-type gallium nitride compound semiconductor by a vapor phase epitaxy method.
After the gallium nitride-based compound semiconductor layer doped with the type impurities is formed, annealing is performed at a temperature of 400 ° C. or higher.

Annealing: Annealing
After the formation of the gallium nitride-based compound semiconductor layer doped with p-type impurities, may be performed in the reaction vessel, or the wafer may be taken out of the reaction vessel and used in an apparatus dedicated to annealing. Annealing atmosphere is vacuum, N
₂ , in an atmosphere of an inert gas such as He, Ne, Ar, or a mixed gas thereof, and most preferably in a nitrogen atmosphere pressurized at a decomposition pressure of the gallium nitride-based compound semiconductor or more at the annealing temperature. This is because pressurization as a nitrogen atmosphere has an action of preventing N in the gallium nitride-based compound semiconductor from decomposing and leaving during annealing.

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

The annealing temperature is 400 ° C. or higher, preferably 700 ° C. or higher, and the annealing is performed for 1 minute or more, preferably 10 minutes or more. Even at 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 compound semiconductor having excellent crystallinity can be obtained. .

Further, as a means for suppressing the decomposition of the gallium nitride compound semiconductor during annealing, a cap layer may be further formed on the gallium nitride compound semiconductor layer doped with p-type impurities and then annealed. Good. The cap layer is a protective film, which is a p-layer.
After being formed on a gallium nitride-based compound semiconductor doped with a type impurity, the gallium nitride-based compound semiconductor is decomposed not only under pressure but also under reduced pressure and normal pressure by annealing at 400 ° C. or higher. Can be made into a p-type with low resistance.

To form the cap layer, the gallium nitride-based compound semiconductor layer doped with p-type impurities may be formed and then formed in the reaction vessel, or the wafer may be taken out from the reaction vessel. It may be formed by another crystal growth apparatus such as a plasma CVD apparatus. The material of the cap layer may be any material that can be formed on a gallium nitride-based compound semiconductor and is stable at 400 ° C. or higher, preferably Ga _X Al _1-X N (where 0 ≦ X ≦ 1), Si ₃ N ₄ and SiO ₂ can be mentioned, and the kind of material is appropriately selected depending on the annealing temperature. The thickness of the cap layer is usually 0.01 to 5 μm. If it is thinner than 0.01 μm, the effect as a protective film cannot be sufficiently obtained, and if it is thicker than 5 μm, it is troublesome to expose the p-type gallium nitride compound semiconductor layer by removing the cap layer by etching after annealing. Therefore, it is not economical.

[0014]

FIG. 1 is a diagram showing that a gallium nitride-based compound semiconductor layer doped with a p-type impurity is changed to a low-resistance p-type by annealing. The MOCVD method is used to first form a GaN buffer layer on a sapphire substrate, form a GaN layer with a film thickness of 4 μm while doping Mg as a p-type impurity on the sapphire substrate, and then take out the wafer and set the temperature. Is a diagram in which the hole is measured on the wafer after annealing is performed for 10 minutes in a nitrogen atmosphere while changing the temperature, and the resistivity is plotted as a function of the annealing temperature.

As can be seen from this figure, the resistivity of the Mg-doped GaN layer sharply decreases from above 400 ° C., and from 700 ° C. or above, it exhibits a substantially constant low-resistance p-type characteristic, and the annealing The effect is appearing. In addition,
The hole measurement results of the non-annealed GaN layer and the GaN layer annealed at 700 ° C. or higher showed that the GaN layer before annealing had a resistivity of 2 × 10 ⁵ Ω · cm and a hole carrier concentration of 8 × 10 ¹⁰ / cm ^3. On the other hand, the GaN layer after annealing has a resistivity of 2 Ω · cm and a hole carrier concentration of 2 ×.
It was 10 ¹⁷ / cm ³ . In addition, although this figure shows GaN, Ga doped with p-type impurities is also used.
It was confirmed that similar results were obtained with _X Al _{1 -X} N (0 ≦ X <1).

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

In addition, FIG. 2 also shows a wafer in which a GaN buffer layer and a Mg-doped 4 μm GaN layer are formed on a sapphire substrate by the same MOCVD method.
Annealing was performed for 20 minutes in a nitrogen atmosphere at 000 ° C., and H was applied to the p-type GaN layer of the wafer (a) performed under a pressure of 20 atm and the wafer (b) performed at atmospheric pressure.
It is a figure which irradiates e-Cd laser as an excitation light source, and compares and shows crystallinity by the photoluminescence intensity,
The stronger the blue emission 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 GaN layer tends to be thermally decomposed and its crystallinity tends to deteriorate. However, pressurization prevents the thermal decomposition. P-type G with excellent crystallinity
An aN layer is obtained.

Further, FIG. 3 shows a wafer (c) having a GaN buffer layer and a Mg-doped 4 μm GaN layer formed on a sapphire substrate, and an AlN layer of 0.5 μm as a cap layer on the wafer (c). A wafer (d) grown to a thickness of 1000
After annealing at ℃ for 20 minutes in nitrogen atmosphere,
P exposed by removing the cap layer by etching
It is a figure which compares and shows the crystallinity of the type GaN layer by photoluminescence intensity similarly.

As shown in FIG. 3, the p-type GaN layer (c) that has been annealed without growing the cap layer undergoes decomposition at a high temperature when the p-type GaN layer is annealed at high temperature, so that the emission intensity at 450 nm is increased. Becomes weaker. However, by growing the cap layer (AlN in this case), the AlN of the cap layer is decomposed but the p-type GaN layer is not decomposed, and therefore the emission intensity still remains strong.

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

That is, in the growth of the gallium nitride compound semiconductor layer, NH ₃ is generally used as the N source, and it is considered that during the growth, NH ₃ is decomposed to form atomic hydrogen. By combining this atomic hydrogen with Mg, Zn, etc. doped as acceptor impurities,
It is considered that p-type impurities such as Mg and Zn prevent the p-type impurities from functioning as acceptors. Therefore, the gallium nitride-based compound semiconductor doped with the p-type impurity after the reaction has high resistance.

However, by performing annealing after growth, hydrogen bound in the form of Mg-H, Zn-H, etc. is thermally dissociated, and the gallium nitride-based compound semiconductor layer doped with p-type impurities is removed. Since the p-type impurities work normally as an acceptor, the low resistance p
Thus, a gallium nitride-based compound semiconductor is obtained. Therefore, it is not preferable to use a gas containing hydrogen atoms such as NH ₃ and H ₂ in the annealing atmosphere. Further, it is not preferable to use a material containing hydrogen atoms also in the cap layer for the above reason.

[0024]

The present invention will be described in detail with reference to the following examples. [Example 1] First, a well-cleaned sapphire substrate is placed on a susceptor in a reaction vessel. After evacuating the inside of the container, the substrate is heated at 1050 ° C. for 20 minutes while flowing hydrogen gas to remove the oxide on the surface. Then increase the temperature to 5
It was cooled to 10 ° C and T was used as a Ga source at 510 ° C.
The GaN buffer layer has a film thickness of 200 angstrom while flowing MG gas at 27 × 10 ⁻⁶ mol / min, ammonia gas as N source at 4.0 liter / min, and hydrogen gas at 2.0 liter / min as carrier gas. Grow with.

Next, only the TMG gas is stopped and the temperature is set to 103
After raising the temperature to 0 ° C., TMG gas was again added to 54 × 10 ⁻⁶
Cp ₂ Mg (cyclopentadienylmagnesium) gas was newly added at a flow ^rate of 3.6 × 10 ⁻⁶ mol / min for 60 minutes to grow a Mg-doped GaN layer at 4 mol / min.
Grow with a film thickness of μm.

After cooling, the wafer thus grown was taken out of the reaction vessel, placed in an annealing apparatus, and annealed by holding it at 800 ° C. for 20 minutes in a nitrogen atmosphere at normal pressure.

As a result of hole measurement of the p-type GaN layer obtained by annealing, excellent p-type characteristics such as a resistivity of 2 Ω · cm and a hole carrier concentration of 2 × 10 ¹⁷ / cm ³ were shown.

Example 2 In Example 1, after growing the Mg-doped GaN layer, Cp ₂ Mg gas was stopped, and then a GaN layer was grown to a thickness of 0.5 μm as a cap layer.

In the same manner as in Example 1, the annealing apparatus was operated under normal pressure in a mixed gas atmosphere of nitrogen and argon at 80 ° C.
Anneal for 20 minutes at 0 ° C. After that, a layer of 0.5 μm is removed from the surface by dry etching,
The p-type GaN layer was exposed by removing the cap layer, and the hole measurement was performed in the same manner. As a result, excellent p-type characteristics such as a resistivity of 2 Ω · cm and a carrier concentration of 1.5 × 10 ¹⁷ / cm ³ were exhibited. The blue emission intensity of photoluminescence at 450 nm was about 4 times stronger than that in Example 1.

[Example 3] In Example 1, after growing the Mg-doped GaN layer, the wafer was taken out of the reaction vessel and annealed at 20 atm in a nitrogen atmosphere at 800 ° C for 20 minutes. As a result of Hall measurement, it showed excellent p-type characteristics with a resistivity of 2 Ω · cm and a carrier concentration of 2.0 × 10 ¹⁷ / cm ^3, and the photoluminescence intensity of 450 nm was about the same as that of Example 1. It was four times stronger.

Example 4 In Example 1, after the Mg-doped GaN layer was grown, the wafer was taken out of the reaction container and a plasma CVD apparatus was used to deposit a SiO ₂ layer having a thickness of 0.5 μm as a cap layer thereon. It is formed with a film thickness.

In the annealing apparatus, a nitrogen atmosphere,
Anneal for 20 minutes at 1000 ° C. under atmospheric pressure.
After that, the SiO ₂ cap layer was removed with hydrofluoric acid to expose the p-type GaN layer, and the hole measurement was performed in the same manner.
It exhibited excellent p-type characteristics with a resistivity of 2 Ω · cm and a carrier concentration of 2.0 × 10 ¹⁷ / cm ³ . In addition, 4 of photoluminescence
The emission intensity at 50 nm was about 20 times stronger than that of the case where annealing was performed under the same conditions without forming the cap layer.

[Embodiment 5] In Embodiment 1, after the Mg-doped GaN layer is grown, Cp ₂ Mg gas is stopped and new TMA gas is added at 6 × 10 ^-6 mol / min Si.
2.2 × 10 ^-10 mol / min of H ₄ (monosilane) gas to 2
Flowing 0 minutes, n-type Si-doped Ga _{0 .9} Al _0.1
The N layer is grown to a thickness of 0.8 μm.

After stopping the TMG gas, TMA gas and SiH ₄ gas and cooling to room temperature while flowing hydrogen gas and ammonia gas, the wafer was taken out and placed in an annealing apparatus and kept at 700 ° C. for 20 minutes in a nitrogen atmosphere. And do annealing.

Thus, the p-type G is formed on the sapphire substrate.
An element having a single hetero structure in which an aN layer and an n-type Ga _0.9 Al _0.1 N layer were sequentially stacked was obtained. A gallium nitride-based compound semiconductor layer of this device was formed into an n-type Ga _0.9 Al _0.1
A part of the N layer was etched to expose a part of the p-type GaN layer, an ohmic electrode was attached to each layer, and then cut into chips with a dicing saw. Electrodes were taken out from the n-type layer and the p-type layer exposed on the chip and then molded to produce a blue light emitting diode. The characteristics of this light emitting diode are that blue light is emitted with a forward current of 20 mA, a forward voltage of 5 V and an emission output of 90 μW, and the peak wavelength is 43.
It was 0 nm. This light emission output is a high value that has never been reported as the output of the blue light emitting diode.

On the other hand, when a light emitting diode having the same single hetero structure was manufactured without annealing, the light emitting diode had a forward voltage of about 60 V at a forward current of 20 mA and emitted light only slightly. It only glowed yellowish and soon broke, and the emission output could not be measured.

[Embodiment 6] Similar to Embodiment 1, a GaN buffer layer is formed on a sapphire substrate to a thickness of 200 Å.

Next, only the TMG gas is stopped and the temperature is set to 103
After raising the temperature to 0 ° C., TMG gas was again 54 × 10 5.
^-6 mol / min and SiH ₄ (monosilane) gas at a flow rate of 2.2 × 10 ⁻¹⁰ mol / min for 60 minutes to grow a Si-doped n-type GaN layer with a thickness of 4 μm. grow up.

Then, 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 the TMG gas and Cp ₂ Mg gas and cooling to room temperature while flowing hydrogen gas and ammonia gas, the gas flowing in the reaction vessel was replaced with nitrogen gas, and nitrogen gas was flowed in the reaction vessel. The temperature is raised to 1000 ° C. and kept in the reaction vessel for 20 minutes for annealing.

The device thus obtained was used as a light emitting diode to emit light in the same manner as in Example 43.
It exhibits blue light emission with an emission peak near 0 nm, the emission output is 50 μW at 20 mA, and the forward voltage is 2 as well.
It was 4 V at 0 mA. Moreover, when an element having the same structure was manufactured as a light emitting diode without performing annealing, 2
It emitted a slight yellow light at 0 mA and immediately the diode broke.

[0042]

As described above, according to the manufacturing method of the present invention, a gallium nitride-based compound semiconductor, which has not been a p-type having a low resistance even when doped with a p-type impurity, is made a p-type having a low resistance. Therefore, it is possible to manufacture devices having various structures. Further, the conventional method using electron beam irradiation can reduce the resistance of only the uppermost surface, but in the present invention, the gallium nitride-based compound semiconductor layer doped with p-type impurities by annealing can be made to be p-type as a whole. The p-type layer can be formed uniformly in the plane and even in the depth direction, and the p-type layer can be formed on any layer. In addition, since a thick film layer can be formed, a high-luminance blue light emitting element can be obtained.

[Brief description of 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 a comparison of crystallinity of p-type GaN layers according to an example of the present invention by photoluminescence intensity.

FIG. 3 is a diagram showing a comparison of crystallinity of p-type GaN layers according to an example of the present invention by photoluminescence intensity.

Claims (4)

(57) [Claims] 1. After growing a p-type impurity-doped gallium nitride-based compound semiconductor by a vapor phase growth method, 4
A method for producing a p-type gallium nitride-based compound semiconductor, which comprises performing annealing at a temperature of 00 ° C. or higher. 2. The p-type gallium nitride compound semiconductor according to claim 1, wherein the annealing is performed in a nitrogen atmosphere at a pressure higher than the decomposition pressure of the gallium nitride compound semiconductor at the annealing temperature. Production method. 3. The method for producing a p-type gallium nitride compound semiconductor according to claim 1, further comprising forming a cap layer on the gallium nitride compound semiconductor doped with the p-type impurity. . 4. The cap layer is made of any one material selected from Ga _X Al _{1 -X} N (where 0 ≦ X ≦ 1), AlN, Si ₃ N ₄ and SiO _2. The method for producing a p-type gallium nitride compound semiconductor according to claim 3.