JP2000307155A - Light-emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure, of a light-emitting diode(LED) with a high emission efficiency and with a higher output power than conventional with smaller power consumption than conventional, wherein the light omnidirectionally emitted from an active layer of the LED is sufficiently reflected for the entire spectrum. SOLUTION: In an LED where a pair of distributed Bragg reflectors(DBRs) 5 made of two kinds of materials are formed on a substrate 1 and a light- emitting part is formed on the DBRs 5, the layer thicknesses of the DBRs 5 are changed by 30 to 15% in each pair to form a DBR 6 of a multilayer structure consisting of three layers or more and, at least one layer of the constituent layers of this DBR 6 has a thickness equal to an optical length of the 1/4 wavelength of the LED. Moreover, the constituent layers of the DBR 6 are combined with each other so that the energy distribution of the reflection spectrum may be a normal distribution or a logarithmic normal distribution the center of which is the peak wavelength energy of the LED.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (hereinafter, referred to as LE) having low power consumption and high output, and having high luminous efficiency.
D).

[0002]

2. Description of the Related Art LEDs are widely used as light sources for various displays. In particular, light sources for outdoor displays are required to have low power consumption and high output. However, since the light emission of the LED is spontaneous emission light, the spectrum width is wide, and the light is emitted from the active layer in the same direction, so that the available light is small and the output efficiency of the device is low. For this reason, for example, in an AlGaInP-based visible light LED, the current spreading is increased by making the current diffusion layer sufficiently thick, or a distributed Bragg reflector (hereinafter, referred to as a two-layer) formed of only two layers.
By using DBR), light emission to the back side of the substrate is reflected, power consumption is suppressed, and output is increased.

[0003] Japanese Patent Application Laid-Open No. 10-65264 discloses a distributed Bragg reflector and a method of manufacturing the same. Here, a DBR is formed by alternately stacking an InP layer and a GaPSb layer containing InP so as to have an optical length of １ ／ wavelength on the In substrate. By inserting one or several molecular layers of the InP layer into the GaPSb layer, a substrate pull-in effect that matches the lattice constant of the lower layer occurs, and the lattice constant matches the InP layer, stabilizing the composition. It is planned. This indicates that the controllability of the center wavelength is improved, which contributes to the reduction of the threshold value of the laser.

[0004]

However, in a DBR consisting of only two layers, the reflection spectrum is narrow, and the light emitted from the LED is emitted isotropically. Therefore, light that does not enter the DBR perpendicularly is sufficiently reflected. The luminous efficiency was low.

[0005] Further, the coherent light emitted from the active region of the surface-emitting semiconductor laser of the light source for optical communication is highly reflected by the conventional DBR, so that the controllability of the central wavelength of this light is improved, and the laser light is improved. The threshold could be reduced. However, isotropic light emitted from the active layer of the LED as a display light source cannot be sufficiently reflected by the conventional DBR.

[0006] The present invention has been made in view of the above circumstances, and emits light from an LED isotropically emitted from an active layer.
High luminous efficiency LED that reflects enough light over the entire emission spectrum, has lower power consumption and higher output than conventional LEDs
The purpose is to provide a structure.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a pair of DBs made of two kinds of materials on a substrate.
In an LED in which R is formed and a light emitting portion is formed on the DBR, the layer thickness of the DBR is 3% to 15% for each pair.
A DBR having a multilayer structure of at least three layers is formed by changing the thickness, at least one of the constituent layers of the DBR is formed to have an optical length of １ ／ wavelength, and the energy of the reflection spectrum is further increased. The constituent layers of the DBR are combined so that the distribution becomes a normal distribution or a logarithmic distribution centering on the peak wavelength energy of the LED.

With the above structure, the multi-layered DBR of the present invention not only emits light emitted from the LED isotropically from the active layer, but also emits light obliquely to the DBR as well as light incident perpendicularly to the DBR. Light incident in the direction can also be reflected with high efficiency. As a result, an LED with low power consumption and high output and high luminous efficiency can be realized.

[0009]

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

FIG. 1 is an enlarged sectional view of an AlGaInP-based LED according to an embodiment of the present invention.

An n-type conductive GaAs substrate 1 is sequentially grown on a GaAs substrate 1 by epitaxial growth.
aAs buffer layer 2, Al _x Ga _{1 -x} As (0
≦ x ≦ 1), the DBR constituent layer 3, Al _y Ga _1-y A
A DBR constituent layer 4 composed of s (0 ≦ y ≦ 1, x ≠ y) is formed. The DBR 5 formed by the DBR constituent layers 3 and 4 has a layer thickness changed by 3% to 15% to form a DBR 6 having a multilayer structure of at least three layers.
In this DBR 6, the thickness of at least one of the constituent layers is 1 /
The layers are formed so as to have an optical length of four wavelengths, and the constituent layers of the DBR 6 are combined so that the energy distribution of the reflection spectrum becomes a normal distribution or a logarithmic normal distribution centering on the peak wavelength energy of the LED.

Each layer of the DBR 6 is formed, for example, in the lower D
3% to 1 as going upward with respect to the layer thickness of BR5
It is formed to be 5% thick (or thin).

Further, on this DBR 6, a cladding layer 7 made of AlGaInP lattice-matched to GaAs and having an indirect transition type band structure and n-type conductivity is formed.
Al lattice-matched to As and having a direct transition band structure
An active layer 8 which is a light emitting part made of GaInP, and a G
A cladding layer 9 made of an AlGaInP layer lattice-matched to aAs and having p-type conductivity with an indirect transition band structure is formed. Finally, a layer having p-type conductivity and a thickness of 1 [μm] or more is formed. A current diffusion layer 10 made of GaP is formed.

Light emitted from the active layer 8 of the AlGaInP-based LED is isotropic light having a wavelength of 500 to 700 [nm]. This light is transmitted to the DBR 6
Accordingly, not only light incident on the DBR 6 in the vertical direction but also light incident on the DBR 6 in the oblique direction can be reflected with high efficiency.

FIG. 2 shows the wavelength of the reflected light when the light emitted from the active layer 8 which is the light emitting portion of the LED shown in FIG. FIG. 4 is a reflectivity measurement diagram in which is plotted on the vertical axis. Where D
A reflection intensity spectrum distribution a with respect to a wavelength of light incident perpendicular to the BR 6 and a reflection intensity spectrum distribution b with respect to a wavelength of light obliquely incident on the DBR 6 are shown.

As shown in FIG. 2, of the light emitted from the active layer 8, the reflection intensity spectrum distribution b of the light obliquely incident on the DBR 6 is perpendicularly incident on the DBR 6. It can be seen that the intensity is about the same as the reflection intensity spectrum distribution a of the light. Also, the width of the reflection spectrum is sufficiently wide.

As a result, the LED of the present invention is
Despite having the same thickness as D, the light extraction efficiency increased by 20%, the output during constant current operation increased by 20%, and the power consumption at rated output decreased by 20%.

[0018]

As is apparent from the above description,
According to the present invention, the following excellent effects are exhibited.

(1) By changing the layer thickness of the DBR for each pair to form a multi-layered DBR, light emission of the LED isotropically emitted from the active layer is emitted in a direction perpendicular to the DBR. Not only the incident light but also the light obliquely incident on the DBR can be reflected with high efficiency.

(2) As a result, an LED with low power consumption and high output and high luminous efficiency can be realized.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating a reflectance measurement of the light emitting diode shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 GaAs substrate 2 GaAs layer 3 DBR constituent layer 4 DBR constituent layer 5 DBR 6 DBR having a multilayer structure 7 AlGaInP layer 8 AlGaInP active layer (light emitting portion) 9 AlGaInP layer 10 GaP layer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Masatoshi Shibata 3550 Kida Yomachi, Tsuchiura City, Ibaraki Prefecture Within Hitachi Cable Advanced Research Center (72) Inventor Takanobu Tsukamoto 3550 Kida Yomachi, Tsuchiura City, Ibaraki Hitachi Cable Inside Advanced Research Center Co., Ltd. (72) Inventor Taiichiro Konno 3550 Kida Yomachi, Tsuchiura-shi, Ibaraki Hitachi Cable F-term within Advanced Research Center Co., Ltd. 5F041 AA03 AA24 CA12 CA34 CA35 CA36 CA37 EE23

Claims (5)

[Claims] 1. A light emitting diode in which a pair of distributed Bragg reflectors made of two types of materials are formed on a substrate and a light emitting portion is formed on the distributed Bragg reflector, the thickness of the distributed Bragg reflector is reduced. A light emitting diode characterized by forming a distributed Bragg reflector having a multilayer structure of at least three or more layers by changing every pair. 2. The light emitting diode according to claim 1, wherein the layer thickness of the distributed Bragg reflector is changed by 3% to 15% for each pair. 3. The light emitting diode according to claim 1, wherein at least one of the constituent layers of the distributed Bragg reflector has an optical length of １ ／ wavelength in thickness. 4. The light emitting diode according to claim 1, wherein the constituent layer of the distributed Bragg reflector is formed of a semiconductor crystal. 5. A light emission obtained by combining the constituent layers of the distributed Bragg reflector such that the energy distribution of the reflection spectrum of the multilayer Bragg reflector has a normal distribution or a lognormal distribution centered on the peak wavelength energy of the light emitting diode. diode.