JP2001015801A - AlGaInP LIGHT EMITTING DEVICE AND EPITAXIAL WAFER FOR LIGHT EMITTING DEVICE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an AlGaInP light emitting device having a high light emission output and an epitaxial wafer for the light emitting device, by interposing an insertion layer having a larger lattice constant than a p-type clad layer between the p-type clad layer and a p-type current diffusion layer which are made of a p-type AlGaInP compound semiconductor. SOLUTION: An n-type GaAs buffer layer 2, an n-type clad layer 3, an active layer 4 having a composition whose band gap energy is smaller than the layer 3, a p-type clad layer 5 having a composition whose band gap energy is larger than the layer 4, and a p-type GaP current diffusion layer 6 are laminated on an n-type GaAs substrate 1 in sequence. Here, an insertion layer 7 is interposed between the layers 5 and 6, the layer 7 having a larger lattice constant than the layer 5. The carrier concentration of the layer 7 is set to 2×1017 to 5×1018 cm-3.

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 manufactured using an AlGaInP-based epitaxial wafer has been greatly increased. The main demand is for traffic signals, automobile brake lights, fog lights and the like.

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

This light-emitting element has an emission wavelength of 590 nm and is formed on an n-type GaAs substrate 1 by metal-organic vapor phase epitaxy (hereinafter referred to as "MOVPE").
As buffer layer 2, selenium Se (or silicon S
i) n-type AlGaInP cladding layer 3 doped with undoped AlGaInP active layer 4, p-type AlGaInP cladding layer 5 doped with zinc Zn, p-type GaP current diffusion layer doped with zinc (sometimes called a window layer, This structure is called “p-type current diffusion layer”.

[0005]

As a problem of the present invention, there is a phenomenon that zinc used as a p-type dopant of a p-type current diffusion layer is abnormally diffused into a hetero interface or an adjacent layer.

(1) When the AlGaInP-based epitaxial wafer shown in FIG. 2 is used for a light emitting device, the p-type current diffusion layer 6 spreads the current from the electrode in the lateral direction of the chip.
Since a high p-type carrier concentration (about 1 × 10 ¹⁸ cm ⁻³ ) is required, a high concentration of zinc is doped.

(2) Since the p-type current diffusion layer 6 is grown to a thickness of 5 μm or more in order to improve the above-described current diffusivity, the growth time becomes long.

(3) Further, an AlGaInP-based epitaxial wafer for a 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.

[0009] Due to these three factors, diffusion of zinc in an epitaxial wafer is very likely to occur in the epitaxial wafer as a driving force due to heat received during growth. Zinc diffuses from the heavily doped p-type current diffusion layer to the AlGaInP cladding layer and the active layer, which are light emitting regions,
It is known that when the diffusion of zinc occurs, the diffused zinc forms a non-radiative recombination center and deteriorates the luminous output of the light emitting diode. The effect of the non-radiative recombination center by zinc becomes more remarkable by continuous energization, and there is a problem that the reliability of the light emitting diode is remarkably deteriorated.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide an AlGaInP-based light emitting device having a high light emission output and high reliability and an epitaxial wafer for the light emitting device.

[0011]

In order to achieve the above object, an AlGaInP-based light emitting device according to the present invention comprises an n-type clad layer made of at least an AlGaInP-based compound semiconductor on a substrate having n-type conductivity. AlGaInP having a composition whose band gap energy is smaller than that of the cladding layer
In a light emitting device in which an active layer composed of a compound semiconductor, a p-type cladding layer composed of a p-type AlGaInP-based compound semiconductor having a larger band gap energy than the active layer, and a p-type current diffusion layer are sequentially laminated, An insertion layer having a larger lattice constant than the p-type cladding layer is provided between the cladding layer and the p-type current diffusion layer.

In addition to the above structure, the p-type cladding layer and the p-type current diffusion layer of the AlGaInP-based light emitting device of the present invention are preferably layers doped with zinc.

In addition to the above structure, the current diffusion layer of the AlGaInP-based light emitting device of the present invention is preferably a layer made of GaP.

In addition to the above structure, the carrier concentration of the insertion layer of the AlGaInP-based light emitting device of the present invention is 2 × 10 ¹⁷ cm ^-3.
It is preferably at least 5 × 10 ¹⁸ cm ⁻³ .

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

The epitaxial wafer for an AlGaInP-based light-emitting device of the present invention has an n-type clad layer made of at least an AlGaInP-based compound semiconductor and a composition having a band gap energy smaller than that of the n-type clad layer on an n-type conductive substrate. For a light emitting device having a structure in which an active layer made of an AlGaInP-based compound semiconductor, a p-type clad layer made of a p-type AlGaInP-based compound semiconductor having a larger band gap energy than the active layer, and a p-type current diffusion layer are sequentially stacked. In an epitaxial wafer, p
An insertion layer having a larger lattice constant than the p-type cladding layer is provided between the p-type cladding layer and the p-type current diffusion layer.

In addition to the above structure, the p-type cladding layer and the current diffusion layer of the epitaxial wafer for an AlGaInP light emitting device of the present invention are preferably layers doped with zinc.

In addition to the above structure, the current spreading layer of the epitaxial wafer for an AlGaInP-based light-emitting device
It is preferably a layer made of P.

In addition to the above structure, the carrier concentration of the insertion layer of the epitaxial wafer for an AlGaInP-based light emitting device of the present invention is preferably 2 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less.

In addition to the above structure, the insertion layer of the epitaxial wafer for an AlGaInP-based light-emitting device of the present invention is made of AlGaInP-based light emitting device.
It is preferable to be made of an InP-based material.

The present invention relates to a standard AlGaInP-based light emitting diode using an upper electrode as a p-type electrode.
Type current diffusion layer (GaP layer is often used)
And an insertion layer having a lattice constant larger than that of the p-type cladding layer is inserted between the p-type cladding layer and the p-type cladding layer to reduce strain applied to the light-emitting layer, prevent diffusion of impurities into the active layer, and This prevents the output from decreasing.

Here, when an AlGaInP-based LED is manufactured, a material composition is usually selected and grown so that the lattice constant matches that of the substrate from directly above the substrate to the p-type cladding layer. Only from the type current diffusion layer, a GaP layer having a lattice constant mismatch must be grown from the viewpoint of band gap energy, resistivity, device reliability, and the like. Therefore, as a conventional technique, an attempt has been made to insert an intervening layer having an intermediate lattice constant between the p-type cladding layer and the p-type current diffusion layer to reduce lattice distortion.

For example, Japanese Patent Application Laid-Open No. Hei 10-256598 discloses an attempt to improve the crystallinity of a GaP layer grown in a lattice-mismatched system as much as possible. Effect is not seen.

The inventors of the present invention have made various studies and found that the problem of abnormal diffusion of zinc described above is easily diffused from a layer having a small lattice constant to a layer having a large lattice constant, and is difficult to diffuse in the opposite direction. Was found. That is, the present inventors,
When a layer having a lattice constant smaller than that of the p-type cladding layer is laminated on the p-type cladding layer, zinc tends to be abnormally diffused. It has been discovered that zinc diffuses from the current diffusion layer to the intervening layer, but does not diffuse from the intervening layer to the p-type cladding layer or the active layer.

Furthermore, the present inventors are concerned that the crystallinity of the p-type current diffusion layer is originally deteriorated by interposing a layer having a large lattice constant. I found that it was not a minor problem.

[0026]

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

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

This epitaxial wafer is made of n-type GaAs
AlGaInP is formed on the s substrate 1 by MOVPE.
N-type GaAs buffer layer 2 made of a base compound semiconductor, n
AlGaInP cladding layer (hereinafter referred to as “n-type cladding layer”)
That. 3, an undoped AlGaInP active layer (hereinafter, referred to as “active layer”) 4 made of an AlGaInP-based compound semiconductor having a composition smaller in band gap energy than the n-type cladding layer 3, and a p-type composition having a larger band gap energy than the active layer 4. A p-type AlGaInP cladding layer (hereinafter, referred to as a “p-type cladding layer”) 5 made of an AlGaInP-based compound semiconductor, and a p-type GaP current diffusion layer (sometimes called a window layer, but hereinafter, referred to as a “p-type current diffusion layer”). 6 in that the insertion layer 7 having a larger lattice constant than the p-type cladding layer 5 is provided between the p-type cladding layer 5 and the p-type current diffusion layer 6.

The carrier concentration of the insertion layer 7 is 2 × 10 ¹⁷ cm
^The reason for setting ^{-3 to} 5 × 10 ¹⁸ cm ^-3 is 2 × 10 ¹⁷
If it is lower than cm ^−3, the resistivity of the insertion layer 7 increases,
The driving voltage of the light emitting element becomes too high, and 5 × 10 ¹⁸ cm ⁻³
If it is higher than this, the crystallinity of the insertion layer 7 is deteriorated, and the light emission output of the device is reduced, so that a practical light-emitting device cannot be obtained in any case.

The reason why the AlGaInP-based material is selected as the material of the insertion layer 7 is that the same material as that of the active layer 4 and the clad layers 3 and 5 is used to suppress mixing of unnecessary impurities. For example, As generated when using As-based material
This is to eliminate factors that cause deterioration of the device, such as a substitution reaction between As and P in the AlGaInP layer due to the diffusion of GaAs.

The lattice constant of the insertion layer 7 is
The effect of preventing the diffusion of zinc increases as the value increases, but if the difference between the lattice constants is too large, a defect occurs in the insertion layer 7 and the performance of the light emitting element is rather deteriorated. Therefore, the lattice constant of the insertion layer 7 has an optimum range, which varies depending on the material, composition, and epitaxial growth conditions of the insertion layer 7 or the p-type cladding layer 5 serving as an underlayer.

In order to prevent the diffusion of zinc from reaching the active layer 4, an insertion layer having a large lattice constant may be interposed between the p-type cladding layers 5.
A plurality of insertion layers may be inserted therein.

[0033]

EXAMPLE An epitaxial wafer for a red light emitting diode having a light emission wavelength of about 620 nm having a structure as shown in FIG. 1 was produced.

This epitaxial wafer is made of n-type GaAs
An n-type (Se-doped: 1 ×)
10 ¹⁸ cm ⁻³ ) GaAs buffer layer 2, n-type (Se doped: 8 × 10 ¹⁷ cm ⁻³ ) (Al _0.7 Ga _0.3 ) _0.5 In
_0.5 P clad layer (n-type clad layer) 3, undoped (Al _0.15 Ga _0.85 ) _0.5 In _0.5 P active layer (active layer)
4. p-type (zinc-doped) (Al _0.7 Ga _0.3 ) _0.5 In
_{A 0.5} P clad layer (p-type clad layer) 5 is grown,
A 0.1 μm-thick p-type (Al _0.7
Ga _0.3 ) _0.45 In _0.55 Insertion layer (hereinafter referred to as “insertion layer”) 7 is grown by MOVPE, and p
In this case, a current diffusion layer 6 is formed.

MOVPE growth up to the p-type cladding layer 5 is performed at a growth temperature of 700 ° C., a growth pressure of 50 Torr, a growth rate of each layer of 0.3 to 1.0 nm / s, and a V / III ratio of 300 to 600. . The insertion layer 7 has a V / III ratio of 1
The growth rate was set to 00 and the growth rate was 1 nm / s. The zinc concentration of the p-type cladding layer 5 is 5 × 10 ¹⁷ cm ⁻³ , the zinc concentration of the insertion layer 7 is 5 × 10 ¹⁷ cm ⁻³ , and the zinc concentration of the p-type current diffusion layer is 1 × 10 ¹⁸ cm ⁻³ . .

FIG. 2 is a diagram showing the result of SIMS analysis of the zinc concentration distribution in the epitaxial layer shown in FIG. 1. The horizontal axis indicates the depth, and the vertical axis (logarithmic axis) indicates the zinc concentration.

The concentration distribution of zinc in the depth direction in the grown epitaxial layer was almost as expected, and no abnormal diffusion of zinc as in the conventional example was observed. Further, this epitaxial wafer was 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 diameter of 15 μm is formed on the upper surface of the chip.
A circular p-type electrode of 0 μm was formed. The n-type electrode is made of gold germanium, nickel, and gold,
nm, 500 nm in order, and the p-type electrode is gold zinc,
Nickel and gold are 60 nm, 10 nm and 1000 respectively.
nm. As a result of examining the light emission characteristics, the light emission output was 1.2 mW, and the forward operating voltage (when 20 mW was applied) was 2.0 V.

(Comparative Example) Emission wavelength 6 of the structure shown in FIG.
An epitaxial wafer for a red light emitting diode having a thickness of about 20 nm was produced. The epitaxial structure and the growth method were basically the same as those of the example, except that the insertion layer 7 was not formed on the p-type cladding layer 5 but the p-type current diffusion layer 6 was formed.

That is, this epitaxial wafer is
On an n-type GaAs substrate 1, an n-type GaAs buffer layer 2
, An n-type cladding layer 3, an active layer 4, a p-type cladding layer 5, and a p-type current diffusion layer 6 are sequentially laminated.

FIG. 4 is a diagram showing the result of SIMS analysis of the zinc concentration distribution in the epitaxial layer shown in FIG. 3, wherein the horizontal axis represents the depth and the vertical axis (logarithmic axis) represents the zinc concentration.

As a result of SIMS analysis, it was confirmed that zinc in the p-type current diffusion layer 6 was diffused in a large amount into the light-emitting regions of the p-type cladding layer 5 and the active layer 4.

Further, this epitaxial wafer was processed to produce a light emitting diode chip.

As a result of examining the light emitting characteristics of the light emitting diode by assembling the chip with a stem, the light emitting output was 0.6 mW, and the forward operating voltage (at the time of applying a current of 20 mmW) was 2.4 V.

As described above, according to the present invention, it is possible to obtain a light emitting diode having a simple structure, a higher light emitting output and a higher reliability than the conventional one.

Conventionally, since the reproducibility of the zinc diffusion degree is poor, the in-wafer variation of the zinc concentration distribution and the variation between lots are large, causing a deterioration in the uniformity and reproducibility of the element characteristics. However, according to the present invention, diffusion of zinc can be suppressed, and uniformity and reproducibility of element characteristics can be improved.

Further, since a layer having a certain carrier concentration or more can be inserted between the p-type cladding layer and the p-type current diffusion layer with good reproducibility, a light emitting diode having a low operating voltage can be obtained with good reproducibility. Can be

[0047]

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

AlGaIn with high emission output and high reliability
Provision of a P-based light emitting element and an epitaxial wafer for a light emitting element can be realized.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a result of SIMS analysis of a zinc concentration distribution in the epitaxial layer shown in FIG.

FIG. 3 is a structural diagram of a conventional epitaxial wafer for an AlGaInP-based light emitting device.

4 is a diagram showing a result of SIMS analysis of a zinc concentration distribution in the epitaxial layer shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 n-type GaAs substrate (substrate) 2 n-type GaAs buffer layer 3 n-type cladding layer 4 active layer 5 p-type cladding layer 6 p-type current diffusion layer 7 insertion layer

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Naoki Kanada 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable Advanced Research Center Co., Ltd. (72) Inventor Kenji Shibata 5-1-1 Hidakacho, Hitachi-shi, Ibaraki No. F-term in Hitachi Cable Hidaka Plant (reference) 5F041 AA03 AA43 CA35 CA37 CA39 CA49 CA53 CA65 5F073 AA52 AA55 CA13 CB07 CB18 DA05 DA35

Claims (10)

[Claims] 1. An n-type cladding layer comprising at least an AlGaInP-based compound semiconductor and an active layer comprising an AlGaInP-based compound semiconductor having a composition smaller in band gap energy than the n-type cladding layer on a substrate having n-type conductivity. A light emitting device in which a p-type cladding layer made of a p-type AlGaInP-based compound semiconductor having a composition having a bandgap energy larger than that of the active layer and a p-type current diffusion layer are sequentially laminated, wherein the p-type cladding layer and the p-type An insertion layer having a lattice constant larger than that of the p-type cladding layer is provided between the p-type cladding layer and the current diffusion layer.
nP light emitting element. 2. The AlGaInP-based light emitting device according to claim 1, wherein the p-type cladding layer and the p-type current diffusion layer are layers doped with zinc. 3. The AlGaInP-based light emitting device according to claim 1, wherein said current diffusion layer is a layer made of GaP. 4. The carrier concentration of the insertion layer is 2 × 10
AlGaInP-based light emitting device according to claim 1 is ¹⁷ cm ^-3 or more than 5 × 10 ¹⁸ cm ^-3. 5. The AlGaInP-based light emitting device according to claim 1, wherein said insertion layer is made of an AlGaInP-based material. 6. An n-type cladding layer composed of at least an AlGaInP-based compound semiconductor and an active layer composed of an AlGaInP-based compound semiconductor having a composition smaller in band gap energy than the n-type cladding layer on a substrate having n-type conductivity. A light emitting element epitaxial wafer having a structure in which a p-type cladding layer made of a p-type AlGaInP-based compound semiconductor having a composition larger in band gap energy than the active layer and a p-type current diffusion layer are sequentially laminated; An epitaxial wafer for an AlGaInP-based light emitting device, wherein an insertion layer having a larger lattice constant than a p-type cladding layer is provided between the p-type current diffusion layer and the p-type current diffusion layer. 7. The Al according to claim 6, wherein the p-type cladding layer and the current spreading layer are layers doped with zinc.
An epitaxial wafer for a GaInP-based light emitting device. 8. The epitaxial wafer for an AlGaInP light emitting device according to claim 6, wherein the current diffusion layer is a layer made of GaP. 9. The carrier concentration of the insertion layer is 2 × 10
¹⁷ cm ^-3 or more than 5 × 10 ¹⁸ cm ^-3 in the AlGaInP light emitting device epitaxial wafer according to claim 6. 10. The epitaxial wafer for an AlGaInP-based light emitting device according to claim 6, wherein the insertion layer is made of an AlGaInP-based material.