JPH0563236A - Blue light emitting diode - Google Patents

Abstract

PURPOSE:To provide a new structure, by which a p-n junction light emitting diode having a low VF and a high brightness, i.e., a high light emission efficiency can be realized. CONSTITUTION:A blue light emitting diode, in whose structure, on a substrate 1 laminated are in succession a GaxAl1-xN(N buffer layer 2 (where X is in the scope of 0<=X<=1), a GaxAl1-xN layer 3 (0<=X<=1) thereon, wherein a p-type impurity is added, and a GaxAl1-xN layer 4 (0<=X<=1) thereon, wherein an n-type impurity is added.

Description

Detailed Description of the Invention

[0001]

The present invention has a general formula of Ga _X Al _1-X.
The present invention relates to a blue light emitting diode in which a gallium nitride-based compound semiconductor represented by N (0 ≦ X ≦ 1) is stacked on a substrate, and particularly to a structure of a blue light emitting diode having excellent light emitting efficiency.

[0002]

2. Description of the Related Art At present, gallium nitride compound semiconductors represented by the general formula Ga _X Al _{1 -X} N (0≤X≤1) are known as materials for blue and violet light emitting diodes. This material is generally used mainly in metal organic chemical vapor deposition (hereinafter MOCVD).
Call it the law. ) Is grown on a sapphire substrate. Conventionally, the GaN-based compound semiconductor grown by this method has poor crystallinity, and therefore p-type crystals cannot be formed. Therefore, the light emitting diode conventionally made by using this material is not a pn junction light emitting diode,
The light emitting diode has a MIS (Metal-Insulator-Semiconductor) structure.

A blue light emitting diode having a MIS structure is shown in FIG.
, A buffer layer 12 made of AlN and a Si-doped n-type Ga _x Al _{1 -x} N layer 1 are formed on the sapphire substrate 1.
4, a Zn-doped or Mg-doped i-type Ga _x Al ₁ -xN layer 13 is sequentially stacked, and electrodes are taken out from 13 and 14. In the blue light emitting diode having this structure, the resistivity of the i-type Ga _X Al _1-X N layer 4, which is the uppermost layer, is 1
Since it has a high resistance of 0 ⁸ Ω · cm or more, for example, it is necessary to apply a forward voltage (V _F ) of about 30 V or more at a current value of 20 mA to cause light emission, resulting in low light emission efficiency and reliability. However, it was still insufficient for practical use.

[0004]

It is well known that a pn junction is more advantageous than MIS in consideration of luminous efficiency, reliability and the like. As a means for obtaining a p-type crystal, a technique of irradiating the surface of the i-type layer 4 with an electron beam to increase the hole carrier concentration to lower the resistivity of the i-type layer 4 and partially convert it to p-type has been announced. (Applied Physics, 1991, 2
Monthly issue, Volume 60, p163-166).

However, since electron beam irradiation is effective only up to a depth of 0.3 μm to 0.5 μm from the surface, the lower part of the i-type layer 4, that is, the portion in contact with the n-type layer 3 is still the same. Since it has a high resistance, V _F hardly decreases. On the other hand, the i-type layer 4 has a thickness of 0.3 μm to 0.
With a thin film of 5 μm, the electron beam irradiation effect can be obtained to the full depth, the i-type layer 4 is all p-type, and V _F is reduced to about 20 V, but the brightness is lowered. This is because the light emitting layer is a p-type layer in which impurities such as Mg and Zn serve as the emission center or i
Since it is a mold layer, it is desirable that the thickness of those layers is as thick as possible in order to increase the emission centers.

Further, when this method is used, the i-type layer 4 has to be brought to the uppermost layer in order to perform electron beam irradiation. Therefore, if a highly efficient single-hetero structure light emitting diode is to be produced, the cladding layer is used. N-type layer 3 and i-type layer 4
I had to bring it under. For this reason, the crystallinity of the i-type layer 4, which is a light emitting layer, is extremely deteriorated, and it is impossible to manufacture a highly efficient single hetero light emitting diode.

Therefore, the present invention has been made in view of the above circumstances, and provides a novel structure capable of realizing a pn junction light emitting diode having a low V _F and a high luminance, that is, a high luminous efficiency. It is a thing.

[0008]

[Means for Solving the Problems] Japanese Patent Application No. 3-898
No. 40, Ga _X Al _1-X N (where 0 <X
The range is ≦ 1. ) To form a buffer layer,
It was shown that when a Ga _x Al _{1 -x} N layer (0 ≦ X ≦ 1) was grown on it, the crystallinity was dramatically improved and a p-type crystal could be easily obtained. This method uses a conventional AlN buffer layer as the buffer layer.
The crystallinity of the gallium nitride-based compound semiconductor grown thereon is remarkably improved by setting Ga _x Al _{1 -x} N (where 0 <x ≦ 1) rather than by using GaN as the buffer layer. Thus, the most excellent gallium nitride-based compound semiconductor crystal can be obtained.

The present invention has been made based on this finding, and the blue light emitting diode of the present invention has a Ga on a substrate.
_A buffer layer made of _X Al _1-X N (where X is in the range of 0 <X ≦ 1) and Ga _X doped with p-type impurities.
An Al _1-X N (0 ≦ X ≦ 1) layer is laminated, and Ga _x Al _1-X N (0 ≦ X) doped with an n-type impurity is further stacked thereon.
≦ 1) It has a structure in which layers are sequentially stacked.

In the blue light emitting diode of the present invention, for example, sapphire, SiC, Si, GaAs, etc. can be used for the substrate, Si, Sn, etc. for the n-type impurities, and Mg, Zn, Cd, etc. for the p-type impurities. Ca, Be, etc. can be used. Most preferably, the substrate is sapphire, the n-type impurities are Si, and the p-type impurities are Mg and Zn.

The light emitting diode of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the structure of a blue light emitting diode of the present invention. First, a GaN buffer layer 2 is formed on a sapphire substrate 1, and Mg is formed on the buffer layer 2.
A p-type layer 3 made of doped GaN is formed, and an n-type layer 4 made of Si-doped Ga _0.5 Al _0.5 N is sequentially formed on the p-type layer 3.

As described above, when the light emitting diode having the single hetero structure is used, the efficiency of the blue light emitting diode is dramatically improved. Blue light is emitted from the n-type layer 4 to the p-type layer 3
Is caused by radiative recombination through the levels involved in Mg, which occurs in the p-type layer 3. In this structure, holes cannot be injected into the n-type layer 4 because they are blocked by the energy barrier of the n-type layer 4 which is a cladding layer, and remain in the p-type layer, and efficiently with the electrons injected from the n-type layer 4. By radiative recombination, the luminous efficiency of the light emitting diode is dramatically improved.

Usually, the n-type layer 4 of the clad layer has poor crystallinity, and the crystallinity of the gallium nitride-based compound semiconductor layer grown thereon naturally deteriorates. The cause of the deterioration of the crystallinity of the n-type layer 4 of the cladding layer is not clear, but it is considered that it is generally very difficult to form a mixed crystal film of AlN and GaN. Therefore, if the n-type layer 4 of the cladding layer is brought to the uppermost layer, the crystallinity of only this layer is poor and the crystallinity of the other layers is not degraded. Therefore, the crystallinity of the p-type layer 3, which is the light emitting layer, remains very good, and it becomes possible to manufacture a high efficiency light emitting diode having a single hetero structure. Further, since the buffer layer of the blue light emitting diode of the present invention is Ga _X Al _1-X N (where 0 <X ≦ 1), the p-type impurity-doped gallium nitride compound semiconductor formed directly thereon has a high resistance. The p-type has low resistance instead of the i-type, and its crystallinity is much higher than that of AlN as the buffer layer.

In the blue light emitting diode of the present invention, the p-type layer 3 can be further reduced in resistance by heating the p-type layer 3 at a temperature higher than 600 ° C. by annealing or electron beam irradiation. It is possible to realize a highly efficient blue light emitting diode having a single hetero structure.

The annealing temperature is higher than 600.degree. C., preferably 700.degree. C. or higher, in a reaction vessel or in an atmosphere of nitrogen, an inert gas or in a vacuum using an apparatus dedicated to annealing. Regarding this annealing, we have previously filed Japanese Patent Application No. 3-3.
No. 21353.

The electron beam irradiation is carried out by using an electron beam irradiation apparatus (for example, SEM) having a heating stage in the sample chamber, so that the surface temperature of the p-type gallium nitride compound semiconductor layer becomes 600 ° C. or higher. it can. Also, acceleration voltage 1k
The entire wafer may be scanned while the temperature of the p-type gallium nitride compound semiconductor layer is 600 ° C. or higher in the range of V to 30 kV. When the surface temperature is 600 ° C. or lower, the resistivity of the p-type gallium nitride compound semiconductor layer tends not to be lowered so much, and it is preferable to perform electron beam irradiation at 700 ° C. or higher.

[0017]

[Function] The following may be the cause of the decrease in resistivity due to annealing. In the growth of the gallium nitride-based 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. The atomic hydrogen binds to the acceptor impurity, thereby preventing the p-type impurity from functioning as an acceptor. Therefore, p after the reaction
A gallium nitride-based compound semiconductor doped with a type impurity exhibits high resistance. However, by heating after growth, for example, hydrogen bonded in the form of Mg—H is thermally dissociated and goes out from the gallium nitride-based compound semiconductor layer doped with the p-type impurity, and is normally p-type. Since the impurities act as an acceptor, a low-resistance p-type gallium nitride-based compound semiconductor can be obtained.

Similarly, in the electron beam irradiation as well, when the surface temperature exceeds 600 ° C. by the electron beam irradiation, H is released from the p-type gallium nitride compound semiconductor layer, and the resistance becomes p-type. Conceivable.

When annealing or electron beam irradiation is performed at 600 ° C. or higher, the n-type gallium nitride compound semiconductor layer may be decomposed. However, the n-type gallium nitride compound semiconductor layer is usually 1 μm or more in thickness. To form
It has a function as a protective film of the p-type gallium nitride-based compound semiconductor, which is more convenient.

[0020]

EXAMPLES Example 1 First, a well-cleaned sapphire substrate (C surface) is set in a reactor of an MOCVD apparatus, and the reactor is well replaced with hydrogen. Next, while flowing hydrogen, the temperature is raised to 1050 ° C. and kept for 20 minutes to clean the sapphire substrate.

Next, while flowing hydrogen, the temperature is raised to 1050 ° C. and kept for 20 minutes to clean the sapphire substrate. After that, the temperature is lowered to 510 ° C., hydrogen (4) / min of ammonia (NH ₃ ) and trimethylgallium (TMG) 27 × 10 ⁻⁶ mol / min are flowed while adding to hydrogen to 1
Hold for a minute to grow the GaN buffer layer to about 200 Å.

Only TMG is stopped and the temperature is raised to 1030 ° C. When the temperature reaches 1030 ℃, TMG54
× ^10-6 mol / min, trimethyl aluminum (TMA)
6 × 10 ^-6 / min, monosilane (SiH ₄₎ 22 × 10 ^-11
/ Min, and grow for 60 minutes. Si-doped n-type Ga
_0.9 Al _0.1 N is grown to a film thickness of 3 μm.

TMA and monosilane are stopped, biscyclopentadienyl magnesium (Cp ₂ Mg) is newly flowed, and then a Mg-doped GaN layer is grown to a thickness of 1 μm. Thus, an epitaxial wafer was obtained in which a GaN buffer layer 200 angstrom, a p-type GaN layer 3 μm, and an n-type Ga _0.9 Al _0.1 N layer 1 μm were sequentially laminated on a sapphire substrate.

Next, using photolithography, a part of the n-type layer is etched to expose a part of the p-type GaN layer, an Al electrode is formed on the n-type GaN layer, and a p-type Ga layer is formed.
After attaching an Au electrode as an ohmic electrode on the N layer, it was made into a chip shape and molded according to a conventional method to obtain a blue light emitting diode of the present invention.

When the characteristics of this light emitting diode were measured by passing a direct current, the forward voltage was 10 V at 20 mA, the light emission output was 6 μW at 20 mA, and the peak wavelength was 43.
It was 0 nm. The maximum value of external efficiency was 0.05%.

[Embodiment 2] n-type Ga in Embodiment 1
_{After the 0.9} Al _0.1 N layer is grown, the TMG gas, TMA gas, and SiH ₄ gas are stopped, and hydrogen gas and ammonia gas are flown, and the temperature is cooled to room temperature. After that, the wafer is taken out, placed in an annealing apparatus, and annealed at 750 ° C. for 20 minutes. In the structure of this element, the surface n-type G
The a _0.9 Al _0.1 N layer doubles as both a cap layer (a layer that prevents thermal decomposition of GaN) and an n-type layer.

After that, when a light emitting diode was prepared in the same manner as in Example 1, the forward voltage was 5 V at 20 mA, the light emission output was 60 μW at 20 mA, and the peak wavelength was 430 nm.

[Embodiment 3] n-type Ga in Embodiment 1
After growing a _0.9 Al _0.1 N layer, it is similarly cooled to room temperature. After that, the wafer is taken out, placed in an electron beam irradiation apparatus, the temperature of the heating stage is set to 750 ° C., and electron beam irradiation is performed from above the n-type layer at an acceleration voltage of 15 kV.

After that, when a light emitting diode was prepared in the same manner as in Example 1, the forward voltage was 5 V at 20 mA, the light emission output was 57 μW at 20 mA, and the peak wavelength was 430 nm.

[Embodiment 4] In Embodiment 3, the surface temperature of the n-type layer is 75 by electron beam irradiation only without using a heating stage.
It is performed at 0 ° C. while scanning the entire wafer with an electron beam. The temperature of the irradiated surface was measured with a radiation thermometer. Similarly, when a light emitting diode was used, it had substantially the same characteristics as those obtained in Examples 2 and 3.

[0031]

As described above, the blue light emitting diode of the present invention is highly efficient and can be used for applications such as flat panel displays and flat panel color televisions, which have hitherto been impossible. ,unfathomable.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a blue light emitting diode according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a structure of a conventional blue light emitting diode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... GaN buffer layer 3 ... Mg-doped GaN layer (p-type layer) 4 ... Si-doped Ga _0.5 Al _0.5 N layer (n-type layer) 12 ... AlN buffer layer 13 ... i-type Ga _x Al _1-x N layer 14 ... n-type Ga _x Al _1-x N layer

Claims (2)

[Claims] 1. Ga _X Al _1-X N (where X is 0 <X
The range is ≦ 1. ) A buffer layer, and a Ga _x Al _1-x N (0 ≦ X ≦ 1) layer on which a p-type impurity is doped,
Ga _x Al _1-x N (0
A blue light emitting diode having a structure in which ≦ X ≦ 1) layers are sequentially stacked. 2. The Ga _x A doped with the p-type impurity
The blue light emitting diode according to claim 1, wherein the l _1-X N (0 ≦ X ≦ 1) layer is a layer heated at a temperature higher than 600 ° C. by annealing or electron beam irradiation.