JPH03163882A - Light-emitting diode with optical reflection layer - Google Patents

Abstract

PURPOSE:To improve liminous power conversion efficiency by composing an optical reflection layer of plural kinds of light-wave interference type reflection layers including light-wave interference type reflection layers having wavelength selection characteristics centering around a wavelength longer than the central wavelength of light generated from an active layer. CONSTITUTION:A light-emitting diode is constituted of a substrate 12, a buffer layer 14, an optical reflection layer 16, an N-type clad layer 18, an active layer 20, a P-type clad layer 22, a contact layer 24, an N-type ohmic electrode 26 and a P-type ohmic electrode 28. Since the optical reflection layer 16 is organized of plural kinds of reflection layers 30, 32, 34 including light-wave interference type reflection layers 30, 34 having wavelength selection characteristics centering around light having a wavelength longer than the central wavelength of light generated from the active layer 20, even light oblique to the optical reflection layer 16 formed on the side reverse to the optical extracting surface of the active layer 20 is reflected efficiently. Accordingly, luminous power conversion efficiency is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to improvements in light emitting diodes with light reflective layers.

BACKGROUND OF THE INVENTION Light emitting diodes are widely used in optical communications and displays. Such light emitting diodes are generally manufactured using liquid phase epitaxy (LPE) on a semiconductor substrate.
p by an evitaxial or longitudinal method such as the pitaxy method
It is constructed using a diode that forms an n-junction. In addition, one type of light emitting diode has an active layer that generates light to be emitted from a light extraction surface, and a layer that is formed on the opposite side of the active layer to the light extraction surface and that emits light from the active layer to the active layer. Some devices are equipped with a light reflection layer that reflects the light toward the light source, and the light reflected by the light reflection layer is also emitted from the light extraction surface to improve luminous efficiency. For example, JP-A-H]-200
This is what is described in Publication No. 678. In a light-emitting diode equipped with a light-reflecting layer as described above, among the light generated within the active layer, the light directed toward the side opposite to the light extraction surface is reflected toward the active layer by the light-reflecting layer. Therefore, the light extraction efficiency, that is, the luminous efficiency is improved.

Problems to be Solved by the Invention By the way, the light reflecting layer provided in the above-mentioned conventional light emitting diode has a light wave interference type anti-conventional structure, so it has a wavelength selection characteristic that reflects mainly a specific wavelength. Generally, the reflectance is highest near the wavelength of light emitted from the active layer. However, the conventional light emitting diode configured as described above has a problem in that the light emitting efficiency cannot be increased to the extent originally intended.

The present invention has been made against the background of the above circumstances,
The aim is to provide a light emitting diode with a light reflective layer having high luminous efficiency.

Means for Solving the Problems The inventors of the present invention have conducted various studies based on the above circumstances, and have found that the light reflecting layer provided in the light emitting diode not only reflects light at right angles to it but also In order to increase the reflection efficiency, it is desirable to efficiently reflect light that is oblique to the light reflective layer. It has been found that this is one of the reasons why light emitting diodes cannot achieve sufficient luminous efficiency.

The present invention has been made based on this knowledge, and its gist consists of an active layer that generates light to be emitted from a light extraction surface, and a side of the active layer opposite to the light extraction surface. a light reflecting layer formed on the active layer to reflect light from the active layer toward the active layer, and the light reflected by the light reflecting layer is also radiated from the light extraction surface. In the light emitting diode equipped with a reflective layer, the light reflective layer may be of multiple types including a light wave interference type reflective layer having a wavelength selection characteristic centered on light having a longer wavelength than the center wavelength of light generated from the active layer. The reason is that it is composed of a light wave interference type reflective layer.

Operation and Effect of the Invention In this way, the light reflection layer includes a plurality of light wave interference type reflection layers having a wavelength selection characteristic centered on light having a longer wavelength than the center wavelength of the light generated from the active layer. Since it is composed of different types of reflective layers, even oblique light is efficiently reflected from the light reflective layer formed on the opposite side of the light extraction surface of the active layer, greatly increasing the light emitting efficiency of the light emitting diode. be.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a perspective view of a light-emitting diode IO which is an embodiment of the present invention, and FIG. 2 is a diagram for explaining its laminated structure. In those figures, the light emitting diode 10 is a double heterostructure surface emitting type light emitting diode,
On the n-GaAs single crystal substrate 12, n Ga
+-o. ssA! ! ．． O-0. 45A S buffer layer 14, light reflective layer 16, n Gao. ssAI! ．． o.
asAs layer 18, p-GaAs active layer 20, p-GaO
．． SSA E o. a, A S layer 22, and P”
The GaAs:l contact layer 24 has a thickness of 0.01 to several μm.
They are each provided with a film thickness on the order of . An n-type ξ ohmic electrode 26 made of Au--Ge is provided on the bottom surface of the substrate 12, while a p-type ohmic electrode 28 made of Au--Zn is provided on the contact layer 24.

The buffer layer 14, the light reflection layer 16, the n-type cladding layer l8,
The active layer 20, the P-type cladding layer 22, and the contact layer 24 are sequentially formed in a single crystal state on the substrate 12 by, for example, a metal organic chemical vapor deposition method, a molecular beam epitaxy method, or a vapor phase epitaxy method. It is formed by being made a preceptor.

The light reflecting layer 16 includes three types of first reflecting layers 30 that reflect light by light wave interference and have mutually different wavelength selection characteristics;
It is composed of a second reflective layer 32 and a third reflective layer 34. As shown in an enlarged view in FIG. 3, the first reflective layer 30 has 6
A 2 nm thick GaAs layer and a 68 nm thick Alo.
asGao. 5. 14 pairs of As layers are laminated to form a so-called superlattice, and the wavelength is such that light with a wavelength of 895 nm that is incident in a direction perpendicular to the light reflection N16 has a maximum reflectance. It has selective properties. Also,
The second reflective layer 32 provided on the substrate 12 side of the first reflective layer 30 has six
0 nm thick GaAs layer and 65 nm thick A1
o. asG ao. Seven pairs of ssA and s layers are laminated to form a so-called superlattice, and the wavelength selection characteristic is such that light with a wavelength of 860 nm that is incident in a direction perpendicular to the light reflection layer 16 has a maximum reflectance. It is equipped with The third reflective layer 34 provided on the substrate 12 side of the second reflective layer 32 includes a 67 nm thick GaAs layer and a 74 nm thick Afio. 4sGao. ssA S layer and 1
By stacking two pairs, it forms a so-called superlattice, and the light enters the light reflecting layer 16 in a direction perpendicular to the light reflecting layer 16.
It has wavelength selection characteristics such that light with a wavelength of 8 nm has a maximum reflectance.

The GaAs layer constituting the light reflecting layer 1G and AI! . ．． 4
5G ao. The ssA S layer is layered alternately by switching the raw material gas by operating a valve while maintaining the temperature of the substrate 12 in the chamber at 850°C, and by controlling the flow time of the raw material gas. Obtain the desired thickness. For example, when disciplining the GaAs layer, T
The flow rate of MG gas is 2.2×10-'mole/min,
The flow rate of 10% diluted AsH,l gas was 510cc/m.
in, 10 ppm diluted H2Se gas flow rate 2 8
．． 3 cc/min. Also, A l o1sG
a o. When forming the ssA S layer, TMG
The gas flow rate is 2.2X10-5mole/IIlin,
TMA gas flow rate 7.8X10-bmole/
min, the flow rate of 10% diluted AsHs gas is 5 1 1c
c/min, 10 ppm dilution H. Se gas flow rate 2
8. 3 cc/min. And the above Ga
The period and AI that form the As layer! . , 45G ao.
AsH3 gas is allowed to flow for 10 seconds between the period of forming the ssA S layer.

In the light emitting diode 10 configured as described above, light having a wavelength of 880 nm is generated from the active layer 20 by passing a driving current between the ohmic electrodes 26 and 28. Light traveling from the active layer 20 toward the light extraction surface 36 is emitted from the light extraction surface 36, while light traveling from the active layer 20 toward the substrate 12 is reflected by the light reflecting layer l6 into the active layer 2.
0 and passes through the active layer 20 to the light extraction surface 3.
Emitted from 6. At this time, from the active layer 20 to the substrate 12
The light directed to the side is not only perpendicular to the light reflecting layer 16 but also often obliquely to the light reflecting layer 16. As described above, the light reflective layer l6 includes the first reflective layer 30 and the third reflective layer 34, which have a wavelength selection characteristic having a center wavelength longer than the wavelength of 880 nm of the light generated from the active layer 20. Therefore, even light oblique to the light reflecting layer 1G is efficiently reflected by the light reflecting layer 16. Therefore, according to the light emitting diode 10 of this embodiment, the wavelength of light perpendicular to the light reflecting layer 16 is efficiently reflected. The light emitting efficiency is several tens of percent higher than that of a conventional light emitting diode equipped with a light wave interference type reflective layer having a single wavelength selection characteristic.

Further, according to the light emitting diode 10 of this embodiment, the buffer layer 1 is placed on the substrate 12 while the substrate 12 is placed in the chamber.
4, light reflective layer 16, n-type cladding layer 18, active layer 20,
Since the p-type cladding layer 22 and the contact layer 24 need only be epitaxially grown in sequence, there is an advantage that manufacturing is easy and the light emitting diode 10 is inexpensive. For example, metal organic chemical vapor deposition (MOCVD) is a method for evitaxial enhancement.
Chemical Vapor Depositio
n) method and molecular beam epitaxy (MBHHMolecul)
ar Beam Epitaxy) method, or vapor phase epitaxy (VPEHVapor Phase Epitaxy) method.
axy) method, etc. are preferably used, and among them, the organometallic chemical vapor phase method can easily form a precise and uniform thin film, so it forms a high-quality GaAs/AIGaAs superlattice layer. Particularly desirable above.

Furthermore, since the light reflecting layer 16 is composed of a GaAs/Aj2GaAs superlattice layer, the n-GaAs substrate l2
Ya n A l. 0. 3SG a 0. 6SA
A high-quality light emitting diode 10 can be obtained without causing lattice mismatch with the S cladding layer l4.

Although one embodiment of the present invention has been described above in detail based on the drawings, the present invention can also be implemented in other embodiments.

10 For example, the light emitting diode lO of the above embodiment is made of GaAs
/ A f! Although the GaAs double heterostructure is used, the present invention is also applicable to light emitting diodes made from other compound semiconductors such as GaP, InP, and InGaAsP, and to light emitting diodes with a single heterostructure or homostructure. may be applied.

Further, in the above embodiment, the light reflecting layer 16 is made of GaAs.
/ AE Ga As superlattice layer is provided, but it is also possible to use a light reflecting layer made of other semiconductor materials in consideration of refractive index and the like.

Further, in the above embodiment, the active layer 20 and the light reflecting layer 16 were provided in parallel, but they do not necessarily have to be parallel.
Moreover, the active layer 20 may be provided in a part.

Further, the light reflecting layer 16 of the above-mentioned embodiment is similar to the first reflecting layer 30.
, the second reflective layer 32, and the third reflective layer 34 are sequentially laminated, but the lamination order may be different from that described above.

Although no other examples are given, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a light emitting diode which is an embodiment of the present invention. FIG. 2 is a sectional view illustrating the laminated structure of FIG. 1. FIG. 3 is an enlarged view of the light reflecting layer of the light emitting diode shown in FIG. 1. 10: Light emitting diode 16: Light reflective layer 20: Active layer 30: First reflective layer (light wave interference type reflective layer) 32: Second reflective layer (light wave interference type reflective layer) 34: Third reflective layer (light wave interference type reflective layer) Layer) 36: Light extraction surface

Claims (1)

[Claims] An active layer that generates light to be emitted from a light extraction surface;
a light reflection layer formed on the opposite side of the light extraction surface of the active layer to reflect light from the active layer toward the active layer, and the light reflected by the light reflection layer also reflects the light from the light extraction surface. In a light-emitting diode equipped with a light-reflecting layer that emits light from a surface, the light-reflecting layer has wavelength-selective characteristics that center on light having a longer wavelength than the center wavelength of light emitted from the active layer. 1. A light-emitting diode comprising a light-reflecting layer, the light-emitting diode comprising a plurality of types of light-wave interference-type reflective layers, including a light-wave interference-type reflective layer.