JP2001036137A - Epitaxial wafer and light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial wafer which is capable of realizing an LED of high output power, contains at least Ga as a component element, and is provided with a P-type layer. SOLUTION: A compound semiconductor epitaxial wafer contains at least Ga as a component element and is provided with a P-type layer 30. The P-type layer 30 has such a carrier concentration profile, where the carrier concentration of the P-type layer 30 is as high as 0.8 to 80×1018 cm-3 at its edge on the side of a board 10 and is decreased gradually, as the part of the layer 30 is located is located more distant from the board 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a compound semiconductor epitaxial wafer and a light emitting diode (hereinafter, “LED”).

[0002]

2. Description of the Related Art LEDs using a semiconductor crystal as a constituent material are now widely used as display elements. Among them
III-V compound semiconductors have band gaps corresponding to the wavelengths of visible light and infrared light, and thus have great advantages when applied to light-emitting elements. Therefore, the group III-V compound semiconductor is L
It is used as a material for most EDs, especially for Ga.
AsP is in great demand for LEDs. These materials are required to improve light emission output, which is the most important characteristic of LEDs.

FIG. 2 shows that GaAs is formed on a GaP single crystal substrate.
₁ shows the structure of a general epitaxial wafer having an epitaxial layer of _1-x P _x (0.45 ≦ x <1). This epitaxial wafer has an n-type GaP single crystal substrate 20 and a homo layer 24 having the same composition as the substrate and a mixed crystal ratio x of 1.0 in order to alleviate the difference in lattice constant between the substrate and the uppermost layer. The GaAs _1-x P _x composition change layer 21, the GaAs _1-x0 P _x0 constant composition layer 22, and the GaAs _1-x0 P _x0 low carrier concentration constant composition layer 23 doped with nitrogen (N) are changed to _{ｘ x 0.} It has a structure of epitaxial growth.

In this epitaxial wafer, the low carrier concentration constant composition layer 23, which is the uppermost layer, becomes the light emitting layer. When the composition of the constant composition layer 23 is changed, the band gap also changes. Therefore, LE that emits red to green light according to the composition.
D can be manufactured. Therefore, the constant composition layer 23
Usually has a composition of a mixed crystal ratio x ₀ corresponding to the emission wavelength of the LED, and has a predetermined carrier concentration of nitrogen (N) and tellurium (Te) or sulfur (S) as an n-type dopant. Doping as follows. For example, red light emission (wavelength 630n
For m), x ₀ is about 0.65.

In recent years, it has been required to reduce the power consumption of LEDs, that is, to develop LEDs that can obtain high light output with less power consumption. To meet these demands, it has been proposed to improve the quality by improving the epitaxial wafer structure (Japanese Patent Laid-Open No. 6-196756). according to it,
It has been revealed that when the carrier concentration of the N-doped low carrier concentration constant composition layer serving as the light emitting layer is set to 3 × 10 ¹⁵ cm ⁻³ or less, it is possible to simultaneously improve the light output and extend the life.

In order to minimize the destruction of the crystal integrity of the light-emitting layer, prolong the life of the injected carriers, and obtain an LED with a high light output, the carrier concentration is set to 3.5 to 4.5. It has also been clarified that it may be 8.8 × 10 ¹⁵ cm ⁻³ (Japanese Patent Publication No. 58-1539). However, there is a need for even better performance than the performance of LEDs achievable by these conventional techniques.

Generally, the above-mentioned epitaxial layers formed by vapor phase growth are all n-type, and in a subsequent processing step, a constant composition layer doped with N by diffusion from the surface of the epitaxial layer is raised to a depth of about 4 to 10 μm. A p-type layer is formed by diffusing Zn to a concentration.
For example, JP-A-8-335715 discloses that GaAs
The p-type layer of the P epitaxial layer is grown by vapor phase epitaxy to
An n-junction is formed, and a high carrier concentration region on the surface of the p-type layer is formed by diffusion.

However, since it is difficult to control the carrier concentration by such a diffusion method, the carrier concentration is 1 ×.
It will be as high as 10 ¹⁹ cm ^-3 or more. Due to the high carrier concentration and the increase in crystal defects caused by diffusion, the amount of light absorbed by the p-type layer increases, and there is a problem that the improvement in light output is limited.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art. That is, an object of the present invention is to provide an epitaxial wafer having at least Ga as a constituent element and having a p-type layer, which can realize an LED with high light output. Another object of the present invention is to provide an LED having a high light output using the epitaxial wafer.

[0010]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, by optimizing the carrier concentration profile in the p-type layer, an excellent epitaxial layer having the desired effect has been obtained. The inventors have found that a wafer can be manufactured, and have provided the present invention.

That is, according to the present invention, in a compound semiconductor epitaxial wafer having at least Ga as a constituent element and having a p-type layer, the p-type layer has a carrier concentration of 0.8 to 80 × 10 ¹⁸ cm ^{− 3.} An epitaxial wafer comprising a carrier concentration decreasing region having a carrier concentration profile in which the carrier concentration decreases as the distance from the substrate increases. The epitaxial wafer of the present invention has a pn junction,
In addition, it is preferable that the carrier concentration of the p-type layer forming the pn junction is lower than the carrier concentration at the substrate side end of the carrier concentration decreasing region. The present invention also provides an LED manufactured using the above epitaxial wafer.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the epitaxial wafer and the LED of the present invention will be described in detail with reference to FIG. The epitaxial wafer of the present invention is a compound semiconductor epitaxial wafer containing at least Ga as a constituent element and having a p-type layer. The feature is that the p-type layer has a carrier concentration of 0.8 at the substrate side end.
８０80 × 10 ¹⁸ cm ^-3 , and includes a carrier concentration decreasing region having a carrier concentration profile in which the carrier concentration decreases as the distance from the substrate increases. FIG.
FIG. 1 is a sectional view showing a typical embodiment of the epitaxial wafer of the present invention. The epitaxial wafer of FIG.
A homo layer 14, a composition change layer 11, a constant composition layer 12, and a p-type layer 30 are epitaxially grown on a single crystal substrate 10 in this order.

The type of the single crystal substrate 10 is not particularly limited, but usually, either GaP or GaAs is selected. An n-type layer 13 forming a pn junction has a GaAs _1-x P _x (0.45 ≦ x) having an indirect transition type band gap.
In the case of <1), the single crystal substrate 10 is preferably made of GaP in order to be transparent to the emission color of the LED and to obtain a high light output as the LED. The thickness of the single crystal substrate is preferably 200 to 700 μm,
In the case of a single crystal substrate, the thickness is preferably 220 to 350 μm.

Homo layer 14 formed on single crystal substrate 10
Consists of the same crystal as the single crystal substrate 10. The homo layer 14 may not be particularly formed. However, in order to suppress the occurrence of misfit dislocation and obtain stable high luminance, the homo layer 14 is formed to have a thickness of 0.1 to 100 μm, preferably 0.5 to 15 μm. Good to do.

The epitaxial layer formed thereon has a composition different from that of the single crystal substrate and contains at least Ga as a constituent element. For example, GaAsP,
A ternary mixed crystal such as AlGaAs, InGaP, and InGaAs and a binary mixed crystal such as GaP can be exemplified. Above all, GaAsP and GaP are preferable because Demand is large, and GaAsP is particularly effective because it has a large effect when an LED is manufactured.
In particular, when the pn junction is GaAs _1-x P _x (0.45 ≦ x <1)
Is preferred. When the epitaxial layer is viewed from the viewpoint of composition, the embodiment shown in FIG. 1 having at least the composition change layer 11 and the constant composition layer 12 is common. Since the difference in lattice constant between the substrate and the epitaxial layer is large, a constant composition layer with less crystal defects can be obtained by using the composition change layer.

The composition change layer 11 is a layer whose composition changes according to the distance from the substrate. For example, when the single crystal substrate 10 is GaP, the composition change layer 11 is formed of GaAs _1-x P _x
It can be configured such that the mixed crystal ratio x decreases from 1 as the distance from the substrate increases. The mixed crystal ratio x is 0 ≦ x <
It can be varied between 1 but preferably 0.4
Change between 5 ≦ x <1. When the single crystal substrate 10 is made of GaAs, the composition change layer 11 is made of GaAs _1-m
Mixed crystal ratio m increasing distance from the substrate as P _m can be configured to increase from zero. At this time, the mixed crystal ratio m can be changed in a range of 0 <m ≦ 1, but is preferably changed in a range of 0 <m ≦ 0.45.

The composition change of the composition change layer 11 may be continuous or stepwise. Further, it is preferable that the composition change of the composition change layer 11 is a monotonous increase without an opposite composition change portion. In any case, the effect is the same because the specific resistance of the epitaxial layer is determined mainly by the carrier concentration. The carrier concentration of the composition change layer 11 is preferably 0.5 to 30 × 10 ¹⁷ cm ⁻³ . In particular, it ^{must be} 1 × 10 ¹⁷ cm ⁻³ or more, and
It is preferably ¹⁷ cm ⁻³ or less. Above all, 1 on average
It is particularly preferable that the pressure be 10 to 10 × 10 ¹⁷ cm ⁻³ in terms of lowering the forward voltage when the LED is formed and obtaining good crystallinity. When the carrier concentration exceeds 30 × 10 ¹⁷ cm ^-3 ,
There is a tendency that problems such as deterioration of crystallinity and generation of crystal defects on the surface of the epitaxial layer and reduction of light output of the LED occur. The layer thickness of the composition change layer 11 is preferably 2 to 100 μm, more preferably 10 to 80 μm.
m.

On the composition change layer 11, a constant composition layer 12
Is preferably formed, and the surface of the constant composition layer 12 preferably forms a pn junction. n to form a pn junction
GaAs having an indirect transition type band gap on the mold layer side
_{In the case of 1-x} P _x (0.45 <x <1), the n-layer side of the pn junction is a low carrier concentration region. The low carrier concentration region 13 preferably has an average carrier concentration of 20 × 10 ¹⁵ cm ⁻³ or less, more preferably 9 × 10 ¹⁵ cm ⁻³ or less.
If the density is less than 0.1 × 10 ¹⁵ cm ⁻³ , it may be difficult to control the carrier concentration or the specific resistance may be increased to cause an increase in the forward voltage of the LED. In order to obtain a high light output and to stabilize the electric characteristics, the preferable average carrier concentration is 0.5 to 9 × 10 ¹⁵ cm ⁻³ . The thickness of the low carrier concentration region 13 is usually 1 to 100 μm, preferably 1 to 50 μm, more preferably 1 to 100 μm.
25 μm. If it exceeds 100 μm, the forward voltage tends to increase due to an increase in resistance due to the low carrier concentration region.

The constant composition layer 12 other than the low carrier concentration region 13 is preferably set within the same carrier concentration range as the composition change layer 11. In addition, the low carrier concentration region 13
The thickness of the constant composition layer 12 other than the above is preferably 3 to 50 μm, and more preferably 5 to 20 μm in order to avoid an increase in cost due to a longer growth time.

It is preferable that the pn junction 17 is doped with at least N since light output is improved. N doping is not limited to the p-type layer and / or the n-type layer forming the pn junction 17 and / or the low carrier concentration region. Even if any part of the epitaxial layer other than these is doped, no problem occurs because light emission occurs at the pn junction. The composition in the constant composition layer 12 is desirably as constant as possible in order to suppress crystal defects such as misfit dislocations as much as possible. The variation of the composition of the constant composition layer 12 is within ± 0.05, preferably ± 0.
02 or less.

The epitaxial wafer of the present invention has a p-type layer
Is characterized by the following configuration. In other words, the p-type layer
Has a carrier concentration of 0.8 to 80 × 10¹⁸cm^-3So
The carrier concentration decreases as the distance from the substrate increases
It is characterized by including a carrier concentration decreasing region. Paraphrase
If the carrier concentration is 0.8 to 80 × 10 at the substrate side end,
¹⁸cm^-3And toward the edge of the epitaxial layer surface side.
Carrier concentration decreasing area having a profile that decreases
The region is characterized by being included in the p-type layer. From the end on the substrate side
The form that decreases toward the edge of the surface of the epitaxial layer is
It may be continuous or stepwise. Also continuous
The part that decreases gradually and the part that decreases gradually
Is also good. If it decreases continuously, the carrier concentration
May decrease or decrease at a constant rate throughout the region
The rate may have changed. The carrier concentration reduction region is
Carrier concentration should be continuously and smoothly reduced.
Good.

The carrier concentration at the side of the substrate in the carrier concentration decreasing region is 0.8 to 80 × 10 ¹⁸ cm ⁻³ , preferably 1.5 to 30 × 10 ¹⁸ cm ⁻³ , and more preferably. It is 5.2 to 20 × 10 ¹⁸ cm ⁻³ . The carrier concentration at the end of the carrier concentration decreasing region on the epitaxial surface side depends on the thickness of the carrier concentration decreasing region, but is usually 95% to 1% of the substrate side end, preferably 94 to 1%.
0%, more preferably 92 to 30%. When the carrier concentration decreasing region is adjacent to the surface of the epitaxial layer, the carrier concentration generally fluctuates due to roughness, oxidation or the like in a portion of several μm from the surface of the epitaxial layer, usually 1 μm or less. The carrier concentration decreasing region referred to in the present specification does not include a portion that has undergone such a change due to roughness or oxidation.

The thickness of the carrier concentration decreasing region is 0.5 μm
The thickness is preferably 1 to 200 μm, and more preferably 1 to 30 μm in order to reduce light absorption by the p-type layer, since high light output can be obtained. The presence of the reduced carrier concentration region in the p-type layer causes the high carrier concentration region to be disposed in the p-type layer.
The current spread at the time of ED is improved. Further, since the carrier concentration on the surface of the epitaxial layer can be reduced, unnecessary absorption of light by the p-type layer can be suppressed, and a high light output can be obtained.

A plurality of carrier concentration decreasing regions may exist in the p-type layer. The number of the carrier concentration reduced regions in the p-type layer is preferably within three, more preferably within two, and most preferably one. The carrier concentration decreasing region may be included in any part in the p-type layer, but is preferably included in the epitaxial layer surface side of the p-type layer forming the pn junction. In particular, it is preferable that the carrier concentration decreasing region is formed on the epitaxial layer surface side of the p-type region where the carrier concentration at the epitaxial layer side end is 0.8 to 80 × 10 ¹⁸ cm ⁻³ . FIG. 1 illustrates a preferred embodiment of the p-type layer. The p-type layer 30 includes a first p-type layer 31 in contact with the pn junction and a second p-type layer 31 having a high carrier concentration in order to spread a current and obtain a good ohmic electrode.
It is composed of a p-type layer 32. In the embodiment of FIG.
The p-type layer 32 is configured as a carrier concentration decreasing region.

It is preferable that the carrier concentration of the first p-type layer 31 in contact with the pn junction is determined so as to maximize the light output at the pn junction. For this reason, it is preferable that the carrier concentration is lower than the maximum carrier concentration in the carrier concentration decreasing region.
That is, it is preferable that the carrier concentration is lower than the carrier concentration at the substrate-side end of the second p-type layer 32. Specifically, the first p-type layer 3
The average carrier concentration of the portion in contact with the pn junction of No. 1 is 0.0
5 to 5 × 10 ¹⁸ cm ⁻³ , preferably 0.3 to 2 ×
10 ¹⁸ cm ^-3 , more preferably 0.5 to 1.5
× 10 ¹⁸ cm ^-3 . The carrier concentration profile of the portion of the first p-type layer 31 in contact with the pn junction may be constant or may have a gradient. The average carrier concentration can be regarded as an average carrier concentration in a range of 0.5 to 1 μm from the pn junction surface excluding the depletion layer region. In the epitaxial wafer of the present invention, the total thickness of the p-type layer 30 is 1 to 30.
It is preferably 0 μm, more preferably 2 to 100 μm, and particularly preferably 3 to 50 μm because the light output of the LED is highest.

The carrier concentration profile in the epitaxial layer is determined by obliquely polishing the epitaxial layer, forming a Schottky barrier diode on the surface thereof,
It can be measured by the V method. In particular, for the measurement of the carrier concentration profile of the p-type layer, a method of directly measuring the epitaxial layer with an electrolytic solution, such as a semiconductor profile plotter PN4300 manufactured by Bio-Rad Laboratories Japan, is effective.
In FIG. 1, the p-type layer 30 includes a first p-type layer 31 and a second p-type layer 32.
Although a two-layer structure is shown, a p-type layer having an arbitrary carrier concentration profile may be formed between the first p-type layer 31 and the second p-type layer 32. First p-type layer 3
The change in carrier concentration between the first and second p-type layers 32 may be steep or step-like, but is preferably a continuous and smooth case. Further, in the epitaxial wafer of the present invention, another layer may be provided adjacent to the second p-type layer 32 opposite to the first p-type layer 31. In addition,
The p-type layer 30 is generally a constant composition layer having the same composition as the pn junction, but may have a different composition in a region other than the pn junction.

The method for producing the epitaxial wafer of the present invention is not particularly limited. As the epitaxial growth method, it is preferable to use a vapor phase growth method such as a halogen transport method or a metal organic chemical vapor deposition (MOCVD) method since a good crystal with few crystal defects can be obtained. Among them, it is preferable to use a vapor phase growth method having a halogen compound raw material. As the halogen compound raw material, for example, hydrochloric acid gas (H
Any compound containing a halogen element such as Cl) and arsenic trichloride (AsCl ₃ ) can be used. When the epitaxial wafer of the present invention is manufactured by the hydride vapor phase epitaxy method, a hydrogen compound raw material of a group V element is used as a group V raw material, metal Ga and HCl are used as a group III raw material, and the metal Ga is reacted with HCl. And supply it as GaCl into the reaction vessel. On the other hand, chloride vapor phase epitaxy
For example, in the case of GaAs growth, metal Ga as a group III material and chloride as a group V material are used as materials.
The l ₃ is reacted supplied into the reaction vessel as GaCl and As _4. In addition, regardless of the combination of the raw materials, the same treatment can be performed if the halogen compound is contained in the raw materials. It is most advantageous to use the hydride vapor phase epitaxy because it is mass-producible and high-purity crystals can be obtained.

When a halogen compound is included in the reaction of epitaxial growth, it is difficult for a p-type dopant to be doped at a high concentration in the epitaxial layer. As the p-type dopant, there are Zn, Mg, Cd, Be and the like, but Zn and Mg are preferable since they have relatively low toxicity. Since a high-purity raw material can be obtained as a doping gas, diethyl zinc (C ₂ H ₅ ) ₂ Zn is used as Zn, and cyclopentadienyl magnesium (C ₅ H ₅ ) Mg or (C ₅ H ₅ ) is used as Mg.
₂ Used as an organometallic compound such as Mg.

Conventionally, it has been difficult to dope Zn to a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ or more.
It is particularly preferable to select Zn because D provides high light output and has low harmfulness. Research has shown that it is possible to dope to 5 to 30 × 10 ¹⁸ cm ⁻³ by making the supply amount of the doping gas extremely large. In manufacturing the epitaxial wafer of the present invention, the growth of a low carrier concentration layer, the formation of a pn junction,
The mold layer growth process can be performed continuously in the same growth process,
It is preferred to make the invention more effective.

Using the epitaxial wafer of the present invention, L
An ED can be manufactured. The configuration and manufacturing method of the LED of the present invention are not particularly limited, and the LED can be manufactured using a normal method used when manufacturing an LED from an epitaxial wafer. As a preferred embodiment of the LED of the present invention, an LED whose sectional view is shown in FIG.
Can be mentioned. The LED shown in FIG. 3 is manufactured by providing electrodes 18 on the epitaxial layer side and the substrate side of the epitaxial wafer of the present invention. When an LED of the same type is manufactured using a conventional epitaxial wafer, the current does not spread to the entire pn junction 17 due to the low carrier concentration of the p-type layer, and light is mainly emitted under the electrode 18, so that the light output Does not improve. Such a problem can be solved by using the epitaxial wafer of the present invention having the second p-type layer 32, and a high-output LED can be manufactured.

[0031]

The present invention will be described more specifically with reference to the following examples. The materials, usage amounts, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following specific examples. In the following description, SC converted to a standard state as a gas flow rate unit will be described.
CM was used. (Example) GaP substrate and high-purity gallium (Ga)
Was placed at predetermined locations in an epitaxial reactor having a quartz boat for a Ga reservoir. As a GaP substrate, sulfur (S) is 3 to 10 × 10 ¹⁷ atoms / cm.
^{3 A} GaP substrate having a circular shape with a diameter of 50 mm and a plane deviated by 10 ° in the [001] direction from the (100) plane was used. These were simultaneously placed on the holder. The holder was rotated three times per minute.

Nitrogen (N ₂ ) gas is introduced into the reactor for 15 minutes.
After introducing air for 9 minutes and sufficiently removing the air, 9600 SCCM of high-purity hydrogen (H ₂ ) was introduced as a carrier gas,
The flow of N ₂ was stopped to start the temperature raising step. After confirming that the temperatures of the Ga-containing quartz boat installation part and the GaP single crystal substrate installation part were maintained at constant temperatures of 800 ° C. and 930 ° C., respectively, by measuring a thermocouple disposed outside the reactor, GaAs with a peak emission wavelength of 630 ± 5 nm
The vapor phase growth of the s _1-x P _x epitaxial film was started. First, 15 SCC of diethyl tellurium ((C ₂ H ₅ ) ₂ Te) which is an n-type impurity diluted with hydrogen gas to a concentration of 50 ppm.
M as a raw material for the Group III element of the periodic table
To generate Cl at 369 SCCM, high-purity hydrogen chloride gas (HCl) was added to the Ga reservoir in the quartz boat at a rate of 36 / min.
9 cc was blown out and blown out from the upper surface of the Ga reservoir. In addition, as a Group V element component of the periodic table, a concentration of 10% by H ₂
Phosphate (PH ₃ ) diluted to 737 SCCM / min
During the introduction, a GaP layer as a first layer was grown on a GaP single crystal substrate for 20 minutes.

Next, the amount of hydrogen arsenide (AsH ₃ ) diluted to a concentration of 10% with H ₂ was determined without changing the amount of each of the gases (C ₂ H ₅ ) ₂ Te, HCl and PH _3. , 0SCCM
From 492SCCM to GaP
The temperature of the substrate was gradually lowered from 930 ° C. to 870 ° C., and a GaAs _1-x P _x epitaxial layer as the second layer was grown on the first layer for 90 minutes. For the next 30 minutes, the introduced amounts of (C ₂ H ₅ ) ₂ Te, HCl, PH ₃ and AsH ₃ were adjusted to 15 SCCM, 369 SCCM and 858, respectively.
A third layer, a GaAs _1-x P _x epitaxial layer, was grown on the second layer while keeping constant at SCCM and 492 SCCM.

For the next 20 minutes (C_TwoH_Five)_TwoTe, HC
l, PH_Three, AsH_ThreeDo not introduce without changing the amount of
Add N iso-electronic trap to this
214SCCM high-purity ammonia gas (N
H_Three) Is added to form the fourth layer GaAs._1-xP_xEpitaki
A char layer was grown on the third layer. For the next 10 minutes (C
_TwoH_Five)_TwoTe, HCl, PH_Three, AsH_Three, NH_ThreeAmount introduced
To supply p-type dopants without changing
The temperature was kept constant at 25 ° C (C_TwoH_Five)_TwoBon with Zn
H_TwoIntroduce 15 SCCM of gas (C_TwoH_Five)_TwoZn steam
Be careful, H_TwoIntroduce the gas and it is the fifth layer
p-type GaAs_1-xP _xAn epitaxial layer is formed on the fourth layer.
Lengthened.

For the next 40 minutes, (C ₂ H ₅ ) ₂ Te, HC
l, (C ₂ H ₅ ) ₂ Zn without changing the introduction amount of PH ₃
Is rapidly increased to 120 SCCM and then gradually reduced to 60 SCCM, and the sixth layer, p-type GaAs
An s _1-x P _x epitaxial layer was grown on the fifth layer and the vapor phase growth was terminated. The thickness of each of the first to sixth layers is 4 μm.
m, 39 μm, 13 μm, 9 μm, 5 μm and 15 μm.

The carrier concentration of the first to fourth layers was measured by polishing the epitaxial layer obliquely by about 1 ° to produce a Schottky barrier diode on the surface. The carrier concentration of the first to third layers was 2-3 × 10 ¹⁷ cm ⁻³ . The fourth layer was n-type and had a carrier concentration of 3 × 10 ¹⁵ cm ⁻³ . The carrier concentration of the fourth layer was almost the same even when a reverse voltage was directly applied to the pn junction after the LED was formed and the CV measurement was performed.

The carrier concentration of the fifth and sixth p-type layers is
The Bio-Rad Laboratory Semiconductor
Measured by profile plotter PN4300
Was. The carrier concentration of the fifth layer is 1 adjacent to the pn junction surface.
0.7 × 10 including μm¹⁸cm^-3Met. 6th layer
The carrier concentration is 6 × 10
¹⁸cm^-3And the epitaxial layer surface side end is 3 × 10¹⁸
cm^-3Met. 6th layer carrier concentration profile
From the substrate side edge to the epitaxial layer surface side edge.
(50% of the edge on the substrate side)
Decrease). Subsequently, electrode formation or the like is performed by vacuum evaporation to obtain 5
00 μm × 500 μm × 280 μm (thickness) prism type L
An ED was formed. Measured without epoxy coat
And the optical output is 98 with 5 chips and the peak wavelength is 630 ±
1 nm.

(Comparative Example 1) In growing the sixth layer, except that the amount of (C ₂ H ₅ ) ₂ Zn introduced was fixed at 60 SCCM, vapor phase growth was carried out under the same conditions as in the example, and an epitaxial wafer was formed. Obtained. The thicknesses of the first to sixth layers are 5 μm, 39 μm, 14 μm, 8 μm, 5 μm, and 15 μm, respectively.
m. When the carrier concentrations of the first to fourth layers were measured in the same manner as in the example, the same value as in the example was obtained. The carrier concentration of the fifth p-type layer is 1 μm adjacent to the pn junction surface.
m was 0.7 × 10 ¹⁸ cm ⁻³ . 6th layer p
The carrier concentration of the mold layer was 3 × 10 ¹⁸ cm throughout the layer.
It was constant at ^-3 . An LED was formed in the same manner as in the example, and the measurement was performed without the epoxy coating. The light output was 62 with five chips, and the peak wavelength was 630 ± 1 nm.

(Comparative Example 2) An epitaxial wafer was obtained by performing vapor phase growth under the same conditions as in the example except that the fourth layer was grown for 70 minutes and the fifth and sixth layers were not grown. The thicknesses of the first to fourth layers are 5 μm, 38 μm, and 12 μm, respectively.
m and 28 μm. When the carrier concentrations of the first to fourth layers were measured in the same manner as in the example, the same value as in the example was obtained. ZnAs _{2 is} applied to the grown epitaxial wafer.
Was diffused from the surface to a depth of 4 μm at a temperature of 760 ° C. by using as a diffusion source to form a p-type layer. The carrier concentration of the p-type layer formed by diffusion is 3.5 × 10 ¹⁹ cm at the surface.
^{Was -3} . An LED was formed in the same manner as in the example, and the measurement was performed without the epoxy coating.
At 8, the peak wavelength was 631 ± 1.

[0040]

The LED manufactured by using the epitaxial wafer of the present invention exhibits a particularly high light output. For this reason,
INDUSTRIAL APPLICABILITY The present invention can be widely applied to various fields, and is expected to contribute particularly to an increase in demand for LEDs.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view showing an example of a layer configuration of an epitaxial wafer of the present invention.

FIG. 2 is an explanatory sectional view showing a general layer configuration of a conventional epitaxial wafer.

FIG. 3 is an explanatory sectional view showing a configuration example of an LED of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 single crystal substrate 11 composition change layer 12 constant composition layer 13 low carrier concentration region 14 homo layer 15 high carrier concentration region 16 epitaxial layer 17 pn junction 18 electrode 20 GaP single crystal substrate 21 GaAs _1-x P _x composition change layer 22 GaAs _1-x0 P _x0 constant composition layer 23 N-doped GaAs _1-x0 P _x0 low carrier concentration constant composition layer 24 GaP homo layer 30 p-type layer 31 first p-type layer 32 second p-type layer (carrier concentration decreasing region)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA03 CA37 CA38 CA48 CA49 CA53 CA55 CA57 CA58 5F045 AA04 AB11 AB17 AC12 AC13 AC15 AC19 AD12 AD13 AF04 AF13 BB16 CA10 DA53 DA58 DA60 5F052 DA04 DB01 GC01 JA08

Claims (3)

[Claims] 1. An element containing at least Ga as a constituent element
In a compound semiconductor epitaxial wafer having a mold layer, the p-type layer has a carrier concentration of 0.8 to
An epitaxial wafer comprising a carrier concentration decreasing region having a carrier concentration profile of 80 × 10 ¹⁸ cm ⁻³ , wherein the carrier concentration decreases as the distance from the substrate increases. 2. The semiconductor device according to claim 1, further comprising a pn junction, wherein a carrier concentration of a p-type layer forming the pn junction is lower than a carrier concentration at an end of the carrier concentration decreasing region on a substrate side. 1 epitaxial wafer. 3. A light emitting diode manufactured by using the epitaxial wafer according to claim 1.