JP2001320083A - AlGaInP LIGHT EMITTING ELEMENT AND EPITAXIAL WAFER THEREFOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable AlGaInP light emitting element having a high emission output, and an epitaxial wafer for light emitting element. SOLUTION: In an A1GaInP material, the degree of diffusion of dopant decreases as the Al composition increases, the dopant is trapped more at an interface as the degree of lattice mismatch increases on the interface, and diffusion from a layer having a larger lattice constant to a layer having a small lattice constant is retarded. Diffusion of dopant from the current diffusion layer 16 side into an active layer 14 can be prevented by inserting a diffusion stop layer 17 of multilayer structure having a high Al composition and different lattice constants between adjacent layers, between the active layer 14 and the p-type current diffusion layer 16. More specifically, effective current diffusion, reduction in working voltage and high optical output can be realized because the dopant is not diffused into the active layer 14 even if the current diffusion layer 16 or a p-type clad layer 15 has a high carrier density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an AlGaInP-based light emitting device and an epitaxial wafer for the light emitting device.

[0002]

2. Description of the Related Art Recently, demand for high-brightness red and yellow light-emitting diodes using an AlGaInP-based epitaxial wafer has been greatly increased. The main application of the light emitting diode is as a traffic signal, an automobile brake lamp, a fog lamp and the like.

FIG. 3 is a sectional view showing a conventional example of an epitaxial wafer for an AlGaInP-based light emitting device.

[0004] The epitaxial wafer 1 is provided on an n-type conductive (n-type) GaAs substrate 2 by a metal organic chemical vapor deposition (MOVPE) method, a buffer layer 3 made of n-type GaAs, and Se (or Si). Doped AlGa
N-type cladding layer 4 made of InP, undoped AlGa
Active layer 5 made of InP, Zn-doped AlGaI
n-type p-type (p-type) cladding layer 6 and Z
An emission wavelength of 590 nm, in which a p-type current diffusion layer (or window layer) 7 made of n-doped GaP is sequentially laminated.
Is an epitaxial wafer for an AlGaInP-based light emitting device.

Incidentally, the AlGaInP-based light emitting device is an n-type G
An electrode is partially formed on the entire lower surface of the aAs substrate 2 and on the p-type current diffusion layer 7 (not shown).

[0006]

Incidentally, in the above-mentioned conventional example, Zn used as a p-type dopant of the p-type current diffusion layer 7 may abnormally diffuse to a hetero interface or an adjacent layer. The p-type current diffusion layer 7 has a high p-type carrier concentration (about 5 × 10 ¹⁸ cm ⁻³ or more) in order to diffuse a current from an electrode not shown in the figure in the plane direction of the chip (lateral direction in the figure).
Is required, so that a high concentration of Zn is doped. The p-type current diffusion layer 7 has a thickness of 5 μm or more in order to improve the abnormal current diffusion described above.
Long growth time. Further, an epitaxial wafer for an AlGaInP-based light emitting device is generally grown at a high temperature of 650 ° C. or higher in order to reduce the concentration of oxygen serving as an impurity.

[0007] Due to these three factors, diffusion of Zn easily occurs in the epitaxial wafer as a driving force by the heat received during growth. Zn diffuses from the heavily doped p-type current diffusion layer 7 to the n-type cladding layer 4 and the active layer 5 which are light emitting regions. When the Zn diffusion occurs, the diffused Zn is non-radiatively recombined. It is known to form a center and reduce the light output of a light emitting diode. The effect of Zn on the non-radiative recombination center becomes more remarkable by continuous energization, and there is a problem that the reliability of the light emitting diode is remarkably deteriorated.

An object of the present invention is to solve the above-mentioned problems and to provide a highly reliable AlGaInP-based light emitting device and an epitaxial wafer for a light emitting device, which have high emission output.

[0009]

In order to achieve the above object, an AlGaInP-based light emitting device according to the present invention comprises an electrode, an n-type conductive GaAs substrate formed on the electrode, and a GaAs substrate.
an n-type clad layer formed on an s substrate and made of an n-type AlGaInP-based material, and formed on the n-type clad layer;
Band gap smaller than n-type cladding layer AlGaI
an active layer made of an nP-based material, and an active layer formed on the active layer;
Higher band gap energy than active layer, p-type Al
AlGa including a p-type cladding layer made of a GaInP-based material, a p-type current diffusion layer formed on the p-type cladding layer, and an electrode partially formed on the p-type current diffusion layer
In the InP-based light emitting device, a diffusion stop layer having a multilayer structure having a band gap larger than that of the active layer and made of two or more kinds of semiconductor materials having different compositions is inserted between the p-type current diffusion layer and the active layer. Things.

In addition to the above constitution, the carrier concentration of the diffusion stop layer of the AlGaInP-based light emitting device of the present invention is 2 × 10 ¹⁷
It is preferably at least cm ^{−3 and at most} 2 × 10 ¹⁹ cm ⁻³ .

In addition to the above structure, the diffusion stop layer of the AlGaInP-based light emitting device of the present invention is preferably made of an AlGaInP-based material.

In addition to the above constitution, it is preferable that the Al composition ratio of each layer of the diffusion stop layer of the AlGaInP-based light emitting device of the present invention is larger than that of the active layer and the p-type cladding layer.

In addition to the above structure, it is preferable that the lattice constant of each layer of the diffusion stop layer of the AlGaInP-based light emitting device of the present invention differs between adjacent layers.

An epitaxial wafer for a light emitting device of the present invention is formed on an n-type conductive GaAs substrate, an n-type cladding layer formed on the GaAs substrate and made of an n-type AlGaInP-based material, and formed on the n-type cladding layer. An active layer made of an AlGaInP-based material having a smaller band gap than the n-type clad layer, a p-type clad layer formed on the active layer and having a larger band gap energy than the active layer and made of a p-type AlGaInP-based material, In an epitaxial wafer for a light emitting device having a p-type current diffusion layer formed on a cladding layer, a band gap between the p-type current diffusion layer and the active layer is larger than that of the active layer and the composition is different. In this case, a diffusion stop layer having a multi-layer structure composed of more than two kinds of semiconductor materials is inserted.

In addition to the above constitution, the carrier concentration of the diffusion stop layer of the epitaxial wafer for a light emitting device of the present invention is 2 ×.
It is preferably 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁹ cm ⁻³ or less.

In addition to the above constitution, the diffusion stop layer of the epitaxial wafer for a light emitting device of the present invention is preferably made of an AlGaInP-based material.

In addition to the above structure, in the epitaxial wafer for a light emitting device of the present invention, it is preferable that the Al composition ratio of each layer of the diffusion stop layer is larger than that of the active layer and the p-type clad layer.

In addition to the above structure, in the epitaxial wafer for a light emitting device of the present invention, it is preferable that the lattice constant of each layer of the diffusion stop layer is different between adjacent layers.

The present inventors have made various studies and found that AlGa
In an InP-based material, the higher the Al composition, the lower the degree of diffusion of the dopant (for example, Zn). The higher the degree of lattice mismatch on the boundary layer surface, the more the dopant is easily trapped at the interface, and the higher the lattice constant. They found that diffusion from layer to layer was less likely.

Therefore, if a multi-layered diffusion stop layer having a large Al composition and a different lattice constant between adjacent layers is inserted between the current diffusion layer and the active layer, dopants from the current diffusion layer side into the active layer can be obtained. Diffusion can be prevented.

That is, even if the current diffusion layer or the p-type clad layer has a high carrier concentration, the dopant does not diffuse into the active layer, so that effective current diffusion, a reduction in operating voltage, and a high light output can be realized.

[0022]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing an embodiment of an epitaxial wafer for an AlGaInP-based light emitting device of the present invention.

The epitaxial wafer 10 has an n-type G
formed on an aAs substrate 11 and a GaAs substrate 11;
Buffer layer 12 of type GaAs, and buffer layer 12
Formed of n-type AlGaInP-based material
Formed on the n-type cladding layer 13 and the n-type cladding layer 13 and having a smaller band gap than the n-type cladding layer 13.
an active layer 14 made of lGaInP-based material;
A p-type cladding layer 15 formed of a p-type AlGaInP-based material having a larger bandgap energy than the active layer 14 and a p-type current diffusion layer 16 formed on the p-type cladding layer 15. A multi-layer structure between the active layer 14 and the p-type current diffusion layer 16 having a band gap larger than that of the active layer 14 and composed of two or more types of semiconductor materials having different compositions (the number is not limited to six in the figure). ) Is the one into which the diffusion stop layer 17 is inserted.

The AlGaInP-based light-emitting device has a structure in which electrodes are partially formed on the entire lower surface of the n-type GaAs substrate and on the p-type GaP current diffusion layer of a chip obtained by dicing the epitaxial wafer 10 (see FIG. 1). Zu.).

The diffusion stop layer 17 preferably has a carrier concentration of 2 × 10 ¹⁷ cm ⁻³ or more and 2 × 10 ¹⁹ cm ⁻³ or less, and is preferably made of an AlGaInP-based material. Each layer 17a of the diffusion stop layer 17, 1
The Al composition ratio of 7b, 17c, 17d, 17e, and 17f is preferably larger than that of the active layer 14 and the p-type cladding layer 15, and the lattice constant of each layer 17a to 17f of the diffusion stop layer 17 is different between adjacent layers. preferable.

(Optimal conditions) Diffusion stop layer 17
If the carrier concentration of is less than 2 × 10 ¹⁷ cm ⁻³ , the resistivity increases and the driving voltage of the light emitting element becomes too high, and the carrier concentration of the diffusion stop layer 17 is higher than 2 × 10 ¹⁹ cm ^−3. This is because the crystallinity is deteriorated and the light emission output of the element is reduced, so that a practical light-emitting element cannot be obtained.

AlGa as a material of the diffusion stop layer 17
The InP type is selected because the active layer 14 and the clad layer 1 are selected.
The use of a material of the same system as that of 3 or 15 is to prevent mixing of unnecessary impurities. For example, the n-type cladding layer 13 made of AlGaInP due to the diffusion of As generated when an As-based material is used. Layer 14 and p-type cladding 1
This is to eliminate factors that cause deterioration of the device, such as a substitution reaction between As and P in No. 5.

Each layer 17a constituting the diffusion stop layer 17
The effect of preventing the diffusion of Zn increases as the lattice constants of .about.17f are larger than each other and as compared with the p-type cladding layer 15, but if the difference in the lattice constants becomes too large, the diffusion stop layer Defects occur in the light emitting element 17, resulting in a decrease in the performance of the light emitting element. Therefore, the lattice constant of each of the layers 17a to 17f constituting the diffusion stop layer 17 has an optimum range.
7-inserting layer or p-type cladding layer 15 serving as a base
The value cannot be limited because it changes depending on the material, composition and epitaxial growth conditions.

As described above, according to the present invention, it is possible to provide an AlGaInP-based light-emitting device and an epitaxial wafer for a light-emitting device having high light emission output and high reliability.

[0031]

Next, the present invention will be described with reference to specific numerical values, but the present invention is not limited thereto.

(Embodiment) Emission wavelength of the structure shown in FIG.
A red light emitting diode epitaxial wafer having a thickness of about 20 nm is manufactured.

An n-type buffer layer 12 made of GaAs (Se doping: 1 × 10 ¹⁸ cm ⁻³ ) and (Al _0.7 Ga _0.3 ) _0.5 In are formed on an n-type GaAs substrate 11 by MOVPE.
N-type cladding layer 13 made of _0.5 P (Se-doped: 1 × 10 ¹⁸ cm ⁻³ ), undoped (Al _0.15 Ga _0.85 ) _0.5
The active layer 14 made of In _0.5 P and (Al _0.7 G
a _0.3 ) _0.5 In _0.5 P (Zn doped: 5 × 10 ¹⁷ cm)
^-3 ) is grown, and (Al _0.8 Ga _0.2 ) _0.51 In is deposited on the p-type cladding layer 15.
_0.49 P layer 17a and (Al _0.8 Ga _0.2 ) _0.5 In _0.5
P layer 17b pair, (Al _0.8 Ga _0.2 ) _0.51 In _0.49
A pair of the P layer 17c and the (Al _0.8 Ga _0.2 ) _0.5 In _0.5 P layer 17d, the (Al _0.8 Ga _0.2 ) _0.51 In _0.49 P layer 17 e and the (Al _0.8 Ga _0.2 ) _0.5 In _0.5 P layer 17
f, a diffusion stop layer composed of three layers (Zn doped: 5
(× 10 ¹⁷ cm ⁻³ ) 17 is formed, and a 10 μm thick p-type current diffusion layer 16 made of GaP (Zn-doped: 1 × 10 ¹⁸ cm ⁻³ ) is grown on the diffusion stop layer 17 by MOVPE. .

A p-type cladding layer 1 made of AlGaInP
MOVPE growth up to 5, a growth temperature of 700 ° C., a growth pressure of 6650 Pa (50 Torr), a growth rate of each layer of 0.3 to 1.0 nm / sec, and a V / III ratio of 200 to 40
Perform at 0. GaP has a V / III ratio of 50 and a growth rate of 1 nm / s.
Grow at ec. The Zn concentration of the p-type cladding layer 15 is 5
× 10 ¹⁷ cm ⁻³ , the Zn concentration of the GaP layer is 1 × 10 ¹⁸ cm
It is ^-3 .

FIG. 2 is a graph showing the concentration distribution of Zn in the depth direction of the epitaxial wafer shown in FIG.
ary Ion Mass Spectorscop
(y: secondary ion mass spectrometry), showing the results of the measurement, wherein the horizontal axis is the depth axis and the vertical axis is the Zn concentration axis.

As shown in the figure, Z diffused from the current diffusion layer
n was almost trapped at the interface of the diffusion stop layer, and no abnormal diffusion of Zn reaching the active layer was observed as seen in a comparative example described later.

Further, the epitaxial wafer 10 is processed to produce a light emitting diode chip. The size of the chip is 300 μm square, an n-type electrode is formed on the entire lower surface of the chip, and a circular p-type electrode having a diameter of 150 μm is formed on the upper surface of the chip (both are not shown). The n-type electrode is made of gold germanium, nickel, and gold each having a thickness of 60 nm and a thickness of 10 nm.
nm, 500 nm in order, and the p-type electrode is gold zinc,
Nickel and gold are respectively 60 nm, 10 nm and 10 nm thick.
Vapor deposition is performed in the order of 00 nm. When such a chip was mounted on a stem (not shown) and the light emitting characteristics of the light emitting diode were examined, the light emitting output was 1.6 mW and the forward operating voltage (20
(at the time of energizing mA) was 1.8 V.

(Comparative Example) Emission wavelength 6 of the structure shown in FIG.
An epitaxial wafer for a red light emitting diode of about 20 nm is manufactured. The epitaxial structure and the growth method are basically the same as those of the above-described conventional example.

FIG. 4 is a diagram showing the results of measurement of the Zn concentration distribution in the depth direction of the epitaxial wafer shown in FIG. 3 by the SIMS method. The horizontal axis is the depth axis, and the vertical axis is the Zn concentration axis. It is.

As shown in the figure, Zn of the current diffusion layer 7 is p-type AlG
It can be seen that a large amount is diffused into the light emitting regions of the aInP cladding layer 6 and the active layer 5. Further, as in the example, the epitaxial wafer 1 was processed to produce a light emitting diode chip, and the light emission characteristics were examined. As a result, the light emission output was 0.6 mW,
The forward operating voltage (at the time of applying a current of 20 mA) was 1.9 V.

From the above, it can be seen that the epitaxial wafer of this embodiment is superior to the epitaxial wafer of the comparative example.

Here, instead of inserting a diffusion stop layer between the current diffusion layer and the p-type cladding layer, a diffusion stop layer may be inserted between the p-type cladding layer and the active layer. In this embodiment, the case where the number of diffusion stop layers is six has been described. However, the present invention is not limited to this.
The number of layers may be less than or equal to seven or more.

Conventionally, to prevent the diffusion of the p-type dopant into the active layer, measures such as using a dopant such as Mg having a small diffusion coefficient or reducing the doping near the active layer in anticipation of the diffusion are taken. Had been taken. But M
g had poor controllability due to the memory effect and doping delay, and when high-concentration doping was performed, even if these measures were taken, diffusion of the dopant into the active layer could not be effectively prevented. . As a result, the doping concentration in the p-type cladding layer and the current diffusion layer must be suppressed, which hinders improvement in device characteristics.

According to the present invention, the diffusion of the dopant is effectively suppressed, so that the dopant such as Zn with good controllability can be doped at a high concentration. As a result, the luminous output is higher than the conventional one, and the reliability is higher. A high light emitting diode can be obtained.

[0045]

In summary, according to the present invention, the following excellent effects are exhibited.

AlGaI with high emission output and high reliability
Provision of an nP-based light emitting device and an epitaxial wafer for a light emitting device can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an epitaxial wafer for an AlGaInP-based light emitting device of the present invention.

FIG. 2 is a view showing a result of measuring a Zn concentration distribution in a depth direction of the epitaxial wafer shown in FIG. 1 by a SIMS method.

FIG. 3 is a cross-sectional view showing a conventional example of an epitaxial wafer for an AlGaInP-based light emitting device.

4 is a diagram showing a result of measuring a Zn concentration distribution in a depth direction of the epitaxial wafer shown in FIG. 3 by a SIMS method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 epitaxial wafer 11 GaAs substrate 12 buffer layer 13 n-type cladding layer 14 active layer 15 p-type cladding layer 16 p-type current diffusion layer 17 diffusion stop layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA04 AA21 AA43 CA04 CA34 CA35 CA37 CA53 CA57 CA65 CA82 CA85 CA92 FF01 5F045 AA04 AB10 AB18 AD11 AE23 AF04 BB16 CA09 DA53 DA60 HA22

Claims (10)

[Claims] An electrode; an n-type conductive GaAs substrate formed on the electrode; and an n-type conductive GaAs substrate formed on the GaAs substrate.
an n-type cladding layer made of an n-type AlGaInP-based material;
An active layer formed on the n-type cladding layer and having a smaller band gap than the n-type cladding layer and made of an AlGaInP-based material; and a p-type layer formed on the active layer and having a larger band gap energy than the active layer. AlGaInP including a p-type cladding layer made of an AlGaInP-based material, a p-type current diffusion layer formed on the p-type cladding layer, and an electrode partially formed on the p-type current diffusion layer In the system light emitting device, a diffusion stop layer having a multilayer structure having a band gap larger than that of the active layer and made of two or more kinds of semiconductor materials having different compositions is inserted between the p-type current diffusion layer and the active layer. A characterized by having
lGaInP-based light-emitting element. 2. The carrier concentration of the diffusion stop layer is 2
AlGaInP-based light emitting device according to × 10 ¹⁷ cm ^-3 or more 2 × 10 ¹⁹ cm ^-3 or less claim 1. 3. The AlGaIn according to claim 1, wherein the diffusion stop layer is made of an AlGaInP-based material.
P-based light emitting element. 4. The AlGaInP-based light emitting device according to claim 1, wherein an Al composition ratio of each layer of the diffusion stop layer is larger than that of the active layer and the p-type cladding layer. 5. The AlGaInP-based light emitting device according to claim 1, wherein a lattice constant of each layer of said diffusion stop layer is different between adjacent layers. 6. An n-type conductive GaAs substrate, and said GaAs substrate.
an n-type cladding layer formed on an s substrate and made of an n-type AlGaInP-based material, and formed on the n-type cladding layer;
AlGa having a smaller band gap than the n-type cladding layer
An active layer made of an InP-based material; and a p-gap formed on the active layer and having a larger bandgap energy than the active layer.
In a light emitting device epitaxial wafer comprising a p-type cladding layer made of a p-type AlGaInP-based material and a p-type current diffusion layer formed on the p-type cladding layer,
A diffusion stop layer having a larger band gap than the active layer and having a multilayer structure composed of two or more semiconductor materials having different compositions is inserted between the active current layer and the active current diffusion layer. Epitaxial wafer for light emitting devices. 7. The carrier concentration of the diffusion stop layer is 2
× 10 ¹⁷ cm ^-3 or more 2 × 10 ¹⁹ cm ^-3 or less at the light-emitting device epitaxial wafer according to claim 6. 8. The light emitting device epitaxial wafer according to claim 6, wherein the diffusion stop layer is made of an AlGaInP-based material. 9. The light-emitting device epitaxial wafer according to claim 6, wherein an Al composition ratio of each layer of the diffusion stop layer is larger than that of the active layer and the p-type clad layer. 10. The epitaxial wafer for a light emitting device according to claim 6, wherein a lattice constant of each layer of said diffusion stop layer is different between adjacent layers.