JPH071799B2 - Semiconductor yellow light emitting diode device - Google Patents

Description

The present invention relates to a light emitting diode, and more particularly to a semiconductor light emitting diode that emits light in the visible region with high brightness.

Visible light emitting diodes have recently been applied as displays for outdoor use and light sources for optical communication.

[Prior Art] Red light emitting diodes, such as Ga _1-x Al _x As light emitting diodes, are very bright and highly efficient.

As a color light source for display or the like, one having a shorter wavelength is desired. In particular, realization of three primary colors is desired. As a yellow light source, a semiconductor light emitting diode having a peak wavelength at 570-600 nm is desired.

InGaP mixed crystal semiconductors and InGaAlP mixed crystal semiconductors are materials with this possibility.

Although it is not a light source for yellow light, a red visible light (660 nm) semiconductor laser is a typical example of a light emitting device using an InGaP-based mixed crystal semiconductor material. FIG. 6 shows an example of a sectional structure of a semiconductor laser using such InGaP as a light emitting layer.

In _1-xy Ga _x Al _y P intermediate clad layer 2, In _x G on GaAs substrate 1
a _1-x P active layer _{3, In 1-xy Ga x} Al y P surface cladding layer 4 are sequentially metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (M
BE) method and other vapor phase growth methods. Full surface electrode 5 on substrate 1, stripe electrode 6 on surface clad layer 4
Is formed.

By passing a current between both electrodes, laser oscillation is induced in the portion of the active layer below the stripe electrode 6.

The structure of this semiconductor laser is the same as that of a light emitting diode (LED) in that it is a diode, but it is significantly different from the LED in terms of a light emitting mechanism and a light emitting direction. To obtain high-efficiency LEDs, technology different from semiconductor lasers is required.

In order to obtain a yellow light source, the mixed crystal composition must be adjusted to the emission wavelength of 570-600nm. Along with this, various adjustments are necessary.

[Problems to be Solved by the Invention] An object of the present invention is to achieve high efficiency with In _1-x Ga _x P or In _1-xy Ga _x Al _y P having a peak emission wavelength in the range of 570 to 600 nm as a light emitting layer. Is to provide a yellow light emitting diode.

[Study carried out to solve the problem] Since LEDs use light emission by spontaneous emission, crystallinity is extremely important. The MOCVD method and MBE method make it difficult to obtain a very high-quality crystal because of its growth mechanism.

Furthermore, unlike a laser, an LED is so-called surface emission that extracts light in a direction perpendicular to the active layer. In order to improve the luminous intensity, it is necessary to improve the luminous efficiency of surface emission, the extraction efficiency of emitted light, and the like. It has been found that the intermediate clad layer under the active layer needs to have a sufficient thickness in order to efficiently emit light emitted in the vertical direction in the active layer and take it out. But,
The MOCVD method mainly used for the growth of the In _1-x Ga _x P system usually yields a thin film of about several μm. Therefore, it is difficult to obtain a highly efficient LED by MOCVD even if a double hetero structure is formed.

[Means for Solving the Problems] In _1-x Ga _x P or In having a peak emission wavelength of 570-600 nm
In addition to providing an intermediate cladding layer made of In _1-xy Ga _x Al _y P with a sufficient thickness between the light emitting layer made of _1-xy Ga _x Al _y P and the GaP substrate, a light emitting diode having a double-hetero structure is formed and the efficiency is improved. Improve.

A clad layer of sufficient thickness can be grown using temperature difference liquid phase epitaxy.

[Function] The light emitting layer of the LED is sandwiched between the clad layers having a wider forbidden band and effectively emits light of 570-600 nm.

Furthermore, since the clad layer between the light emitting layer and the GaP substrate has a sufficient thickness, lattice defects from the substrate and the composition gradient layer can be sufficiently relaxed and the crystallinity can be improved. In addition, the confinement effect, which is a feature of the double hetero structure, appears remarkably, resulting in a highly efficient LED.

[Embodiment] FIG. 1 shows a sectional structure of a light emitting diode according to an embodiment of the present invention. An n-type GaP substrate 11 is used as the substrate crystal, and n-type In _1-xy Ga _x Al _y p (x = 1-0.7, y
= 0-0.2) The composition gradient layer 10 is formed. N-type In _0.1 1Ga _0.7 Al _0.2 P intermediate clad layer 1
2, p-type In _0.3 Ga _0.7 P light emitting layer (or active layer) 13 and p
A type In _0.3 Ga _0.7 Al _0.2 p surface clad layer 14 is epitaxially laminated, and Au-Zn electrodes 16 and Au-Ge-Ni electrodes 15 are formed on the upper and lower surfaces. The composition gradient layer 10 is formed as a buffer layer for absorbing a difference in lattice constant between the GaP substrate 11 and the light emitting layer 13.

FIG. 2 shows the distribution of the forbidden band width (energy gap) of each layer. The forbidden band widths of the GaP substrate 11 and the composition gradient layer 10 are selected to be larger than the forbidden band width of the active layer 13 as shown in FIG. Therefore, of the light emitted from the light emitting portion, the light traveling toward the substrate can be extracted to the outside without being absorbed.

After the In _1-xy Ga _x Al _y P composition gradient layer 10 is formed, the In _1-xy Ga _x Al _y P intermediate cladding layer 12 and In _1-x G are formed by the temperature difference liquid phase epitaxy method.
The a _x P light emitting layer 13 and the In _1-xy Ga _x Al _y P surface cladding layer 14 are epitaxially grown. Here, the clad layer 12 is required to have good crystallinity and a sufficient thickness in order to obtain efficient light emission from the light emitting layer 13. The surface clad layer 14 also has a crystallinity and a thickness capable of forming an effective double hetero structure. Good crystallinity and the required thickness can be obtained by the temperature difference liquid phase epitaxy method.

As shown in Fig. 4, the relationship between the forbidden band width and the lattice constant of InGaP and InAlGaP is InGaAlP having the same lattice constant as InGaP and a large forbidden band.
e) A heterojunction can be formed.

The relationship between the thickness of the cladding layer 12 and the luminous intensity of the light emitting diode is shown in FIG. According to this, the luminous intensity is In _1-xy Ga _x Al
Depending on the thickness of the _y P intermediate clad layer 12, when the thickness is thin, high luminous intensity cannot be obtained, and as the thickness increases, the luminous intensity increases. In order to obtain a sufficient luminous intensity, the thickness of the intermediate cladding layer 12 needs to be 10 μm or more.

To obtain a growth layer that satisfies these conditions,
This is impossible with the MOCVD method and can be achieved by the temperature difference liquid phase epitaxy method. In this method, by strictly controlling the conditions, not only In _1-x Ga _x P but also a thick film of In _1-xy Ga _x Al _y P containing Al can be obtained. This results in a sufficiently thick In
_1-x Ga _x P or In _1-xy Ga _x Al _y P emission layer, In _1-xy Ga _x Al _y
A high-efficiency yellow-emitting LED with a P cladding layer was obtained.

The thickness of the light emitting layer 13 also affects the luminous intensity. If it is too thin, light emission cannot be sufficiently performed, and if it is too thick, the confinement effect due to the double hetero structure cannot be obtained. The thickness may be about 1 μm.

For example, in a GaAlAs double heterostructure light emitting diode, the relationship between luminous intensity and active layer thickness as shown in FIG. 5 is obtained. The optimum thickness is about 1 μm or less. InGaP or InGaAlP
The same relationship can be obtained when the is used as the active layer.

[Advantages of the Invention] A highly efficient LED having an emission peak of 570-600 nm can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional structural view of an LED according to an embodiment of the present invention, FIG. 2 is a graph showing the forbidden band width of each layer in the LED of FIG. 1, and FIG. 3 is a graph showing the thickness of the intermediate cladding layer of the LED and the luminous intensity. Fig. 4 is a graph showing the relationship, Fig. 4 is a graph showing the relationship between the lattice constant of InGaP and InGaAlP and the forbidden band width, Fig. 5 is a graph showing the relationship between the luminous intensity of the GaAlAs double hetero light emitting diode and the active layer thickness, Fig. 6 FIG. 3 is a structural schematic diagram of a semiconductor laser diode using In1-xGaxP as an active layer. Explanation of symbols 10 …… InGaAlP composition gradient layer 11 …… GaP substrate 12 …… InGaAlP intermediate cladding layer 13 …… InGaP light emitting layer 14 …… InGaAlP surface cladding layer 15, 16 …… Electrode

Claims (1)

[Claims] 1. A peak emission wavelength in the range of 570-600 nm I
nGaP or InGaAlP is used as a light emitting layer, and InGaAlP clad layers having a forbidden band width larger than the forbidden band width of the light emitting layer are formed on the GaP substrate by arranging on both sides of the light emitting layer, and between the light emitting layer and the substrate. A semiconductor yellow light emitting diode device, wherein the InGaAlP clad layer is a continuous layer having a thickness of at least 10 μm or more.