JP2001156328A - Epitaxial wafer for light-emitting device and light- emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial wafer for light-emitting devices that can improve light emission intensity and light take-out efficiency, and the light- emitting devices using it. SOLUTION: In the epitaxial wafer for light-emitting devices in multiple quantum well structure where a plurality of barrier layers 7 and well layers 8 are alternately laminated in an active layer 9 on a GaAs substrate 1, the thickness of each well layer 8 is changed, thus distributing a band gap and widening the width (half-value width) of emission spectrum and hence drastically improving the emission intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial wafer for a light emitting device in which an active layer on a GaAs substrate has a multiple quantum well structure in which a plurality of barrier layers and well layers are alternately stacked, and light emission using the same. It relates to an element.

[0002]

2. Description of the Related Art FIG.
Fig. 1 shows a typical structure of an AlGaInP-based light emitting diode epitaxial wafer having an active layer having a multiple quantum well structure with a light emission wavelength of 630 nm among conventional light emitting diode epitaxial wafers.

[0003] As shown in the figure, this epitaxial wafer is formed by metalorganic vapor phase epitaxy (MOVPE).
(Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 3 is laminated on an n-type GaAs substrate 1 with an n-type GaAs buffer layer 2 interposed therebetween, and a multiple quantum well active layer 4 and a P-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 5 and P-type GaP layer 6 are sequentially laminated.

The multiple quantum well active layer 4 has a plurality of un- (Al _0.5 Ga _0.5 ) _0.5 I as shown in FIG.
The structure is such that n _0.5 P barrier layers 7 and un-Ga _0.5 In _0.5 P well layers 8 are alternately and multiplexed.

The multiple quantum well active layer 4
In the light emitting diode obtained by the epitaxial wafer having the above, the brightness is improved about 1.5 times as compared with the light emitting diode of a normal double hetero (DH) structure as shown in FIG. It has been frequently adopted as a light emitting diode of high brightness specification.

On the other hand, in the light emitting diode using such a conventional epitaxial wafer, the luminance is limited to about 100 mcd. Therefore, in order to expand the applicable range in the future, a higher luminance specification is required. Are desired.

Accordingly, the present invention has been devised in order to solve such a problem, and an object of the present invention is to provide a novel epitaxial wafer for a light emitting device capable of greatly improving the luminance as compared with the conventional one. And a light-emitting element using the same.

[0008]

In the multiple quantum well active layer 4, quantum levels are formed on the valence band Ev side and the conductor Ec side of the well layer 8 by the quantum effect as shown in FIG. The energy difference between these quantum levels becomes the substantial band gap of the well layer 8, and the absolute value of the quantum level that determines this band gap is
It is known that the thickness varies depending on the film thickness or composition of the barrier layer 7 or the film thickness or composition on the barrier layer 7 side.

Therefore, in the conventional multiple quantum well active layer 4, as shown in FIGS.
And the well layers 8 have the same thickness and the same composition, respectively, so that the absolute values of the quantum levels of the well layers 8 are all the same, and consequently, the substantial band gap is also reduced in all the well layers 7. Are the same.

If the substantial band gaps of the respective well layers 8 are all the same as described above, the width (half width) of the emission spectrum becomes narrower, and the luminance of the light emitting diode obtained by using the same is obtained. Is difficult to further improve. If the band gaps of all the well layers 8 are the same, light emitted from the well layer 8 located at a position distant from the light extraction surface is absorbed before reaching the light extraction surface. The efficiency was low.

Accordingly, the present invention provides a light emitting device having a multiple quantum well structure in which an active layer on a GaAs substrate has a plurality of barrier layers and well layers alternately stacked, as described in the above claims. In the epitaxial wafer, any one of the film thickness or composition on the well layer side, any one of the film thickness or composition on the barrier layer side, or both layers are not single.

As a result, the absolute value of the quantum level changes and a substantial band gap can be distributed, so that the width (half width) of the emission spectrum can be increased, and the emission intensity can be increased. And the luminance of a light emitting element using the same can be greatly improved.

The substantial band gap of each well layer 8 is gradually increased toward the light extraction surface, so that the substantial band gap of each well layer 8 is gradually increased toward the light extraction surface. Therefore, the absorption of light in the active layer is suppressed, the efficiency of extracting light to the outside is improved, and the luminance can be further improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows an embodiment of an epitaxial wafer for a light emitting device (hereinafter, referred to as an epitaxial wafer) according to the present invention.

As shown in the figure, this epitaxial wafer is formed by a metalorganic vapor phase epitaxy (MOVPE) as in the prior art.
N) (Al _0.7 Ga _0.3 ) _0.5 In on an n-type GaAs substrate 1 via an n-type GaAs buffer layer 2
_{A 0.5} P clad layer 3 is grown, and a multiple quantum well active layer 9 (hereinafter referred to as an active layer 9) is formed on the clad layer 3.
Is formed, and a P-type (Al _0.7 Ga) is formed on the active layer 9.
_0.3 ) _0.5 In _0.5 P clad layer 5 and P-type GaP layer 6 are sequentially grown and stacked in multiple layers.

The active layer 9 includes a plurality of un- (A
l _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layer 7 (hereinafter referred to as barrier layer 7) and un-Ga _0.5 In _0.5 P well layer 8
(Hereinafter, referred to as well layers 8) are alternately grown and stacked in multiple layers.

Here, in the present embodiment, the thickness of each barrier layer 7 is all 10 nm, whereas the thickness of each well layer 8 is gradually reduced in the laminating direction. All film thicknesses are different. Specifically, as shown in FIG. 1 and FIG. 2, the thickness of the well layer 8a farthest from the light extraction surface in each of the well layers 8 is 6.3 nm.
The thickness of the well layer 8g at the position closest to the light extraction surface is 5.7 nm, which is the thinnest state. .

For this reason, as shown in FIG.
When the absolute values of the quantum levels of ~ 8 g are different from each other, the substantial band gap gradually increases toward the light extraction surface.

Therefore, since the substantial band gap of the well layer 8 can have a distribution, the emission spectrum width (half width) is widened, and the emission intensity of the active layer 9 is greatly improved as compared with the conventional one. . In addition, each of the well layers 8a to 8g
The light absorption in the active layer 9 is suppressed by gradually increasing the substantial band gap in the direction of the light extraction surface, so that the efficiency of light extraction to the outside is improved.

The change in the band gap can be obtained not only by changing the thickness of the well layer 8 but also by appropriately changing the thickness of the barrier layer 7 or both layers.
Further, the above-mentioned effect can be achieved by changing the composition of the well layer 8 or the barrier layer 7, and therefore, the same operation and effect as described above can be obtained by these methods. Further, it is possible to change only a part of the well layer 8 (or the barrier layer 7) without changing all the layers.

[0022]

Next, specific examples of the present invention will be described.

(Embodiment) As shown in FIG.
An n-type (Se-doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 3 is provided on an n-type GaAs substrate 1 via an n-type (Se-doped) GaAs buffer layer 2 by a VPE method.
And an emission wavelength of 63 on the cladding layer 3.
A multiple quantum well active layer 9 near 0 nm was formed. Here, the multi-quantum well active layer 9 has a thickness of 10 nm.
Eight-(Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layers 7 and un-Ga _0.5 In _0.5 P well layers 8 are alternately and multiplexed, and the thickness of the well layer 8 is 6.3 n.
A structure in which the thickness was changed in steps of 0.1 nm in the range of m to 5.7 nm so as to become thinner in order in the direction of the light extraction surface was adopted.

Next, p-type (zinc-doped) (Al) is formed on the multiple quantum well active layer 9 by the MOVPE method.
_{The 0.7} Ga _0.3 ) _0.5 In _0.5 P clad layer 5 and the p-type (zinc-doped) GaP layer 6 were each laminated to a thickness of 10 μm to form an epitaxial wafer for a light emitting device according to the present invention. All the epitaxial layers were formed at a film forming temperature of 700 ° C., a film forming pressure of 50 Tool, and a film forming speed of 0.3 to 0.3 ° C.
The measurement was performed at 3.0 nm / s and the V / III ratio was 100 to 600.

Next, the same process as in the prior art was performed on the epitaxial wafer for a light emitting device to produce a light emitting diode chip. The size of this chip was 300 μm square, and an n-type electrode was formed on the entire lower surface of the chip.
A 50 μm circular p-type electrode was formed. The n-type electrode is made of gold germanium, nickel, and gold at 60 nm and 10 nm, respectively.
nm, then 1000 nm, and the p-type electrode is made of gold, zinc, nickel and gold at 60 nm, 10 nm and 10 nm, respectively.
Deposition was performed in the order of 00 nm. Further, this chip was assembled into a stem and the process was performed up to resin molding, and the light emitting characteristics of the light emitting diode were examined.

(Conventional Example) As the multiple quantum well active layer, except that the thicknesses of all barrier layers and well layers are made uniform,
After forming an epitaxial wafer for a light emitting device by the same method as in the first embodiment, the same processing as before was performed on the epitaxial wafer for a light emitting device to produce a light emitting diode having a size similar to that of the embodiment. The light emission characteristics were examined.

First, comparing the emission spectra of the light emitting diodes of the embodiment and the conventional example when a current of 20 mA is applied, as shown in FIG. 3, in the present embodiment, the width of the emission spectrum is wider than that of the conventional example. As a result, the light emission intensity was greatly improved as compared with the conventional example.

Also, as a result of measuring the luminance of both light emitting diodes, the result is 130 mcd in the present embodiment, compared to 100 mcd in the conventional example, and the luminance is 30 mcd in comparison with the conventional example.
% Also improved.

[0029]

In summary, according to the present invention, the thickness or composition of the well layer or barrier layer of the multiple quantum well active layer is varied so as to have a distribution in the band gap, so that the width of the emission spectrum is widened. , Thereby improving the brightness. In addition, since the substantial band gap is widened as the band gap approaches the light extraction surface side, excellent effects such as an improvement in light emission extraction efficiency and further improvement in luminance can be achieved. be able to.

[Brief description of the drawings]

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

FIG. 2 is a conceptual diagram showing a band gap in a multiple quantum well active layer of an epitaxial wafer for a light emitting device according to the present invention.

FIG. 3 shows a light emitting device (light emitting diode) according to the present invention;
FIG. 9 is a graph showing the result of comparing the emission spectra of conventional light emitting diodes.

FIG. 4 is a structural view showing a typical example of a conventional epitaxial wafer for a light emitting device.

FIG. 5 is a graph showing an emission spectrum of a light emitting diode having a conventional double hetero active layer and an emission spectrum of a light emitting diode having a conventional multiple quantum well active layer.

FIG. 6 is an explanatory diagram showing a substantial band gap due to a quantum effect of a multiple quantum well active layer.

FIG. 7 is a conceptual diagram showing a band gap in a conventional multiple quantum well active layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs substrate 2 Buffer layer 3, 5 Cladding layer 4 Conventional multiple quantum well active layer 6 GaP layer 7 Barrier layer 8 Well layer 9 Multiple quantum well active layer of the present invention

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Taiichiro Konno 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Within Hitachi Cable Advanced Research Center (72) Inventor Naoki 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture (72) Inventor Masahiro Noguchi 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Hitachi Cable Co., Ltd. Hidaka Plant (72) Inventor Yukio Kikuchi 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture No. 1 F-term in the Hidaka Plant of Hitachi Cable, Ltd. (reference) 5F041 AA04 AA14 CA05 CA22 CA34 CA65 5F073 AA74 CA07 CB07 DA05

Claims (7)

[Claims] In an epitaxial wafer for a light emitting device having a multiple quantum well structure in which an active layer on a GaAs substrate has a plurality of barrier layers and well layers alternately stacked, the thickness of each well layer is a single. An epitaxial wafer for a light-emitting device, characterized in that: 2. An epitaxial wafer for a light emitting device having a multiple quantum well structure in which an active layer on a GaAs substrate has a plurality of barrier layers and well layers alternately stacked, wherein the composition of each well layer is single. An epitaxial wafer for a light emitting device, characterized in that it is not provided. 3. An epitaxial wafer for a light emitting device having a multiple quantum well structure in which an active layer on a GaAs substrate has a multiple quantum well structure in which a plurality of barrier layers and well layers are alternately stacked, wherein each of the barrier layers has a single thickness. An epitaxial wafer for a light emitting device, characterized in that: 4. In a light emitting device epitaxial wafer having a multiple quantum well structure in which an active layer on a GaAs substrate has a plurality of barrier layers and well layers alternately stacked, the composition of each barrier layer is not unitary. An epitaxial wafer for a light emitting device, characterized in that: 5. In a light emitting device epitaxial wafer having a multiple quantum well structure in which an active layer on a GaAs substrate has a plurality of barrier layers and well layers alternately stacked, a substantial band gap of each well layer is provided. Is not a single epitaxial wafer for a light emitting device. 6. A light emitting device epitaxial wafer having a multiple quantum well structure in which an active layer on a GaAs substrate has a plurality of barrier layers and well layers alternately stacked, wherein a substantial band gap of each well layer is provided. Characterized in that the size of the epitaxial wafer increases toward the light extraction surface. 7. A light-emitting device obtained by using the light-emitting device epitaxial wafer according to any one of claims 1 to 6.