JPS6328510B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to light emitting diodes, and particularly to a so-called light emitting diode array in which a plurality of light emitting diodes are arranged on the same substrate.

As is well known, a light emitting diode (hereinafter abbreviated as LED) is a diode that emits light by passing a forward current through a pn junction formed in a semiconductor crystal.
The important characteristics required for this LED are emission wavelength characteristics, luminous efficiency, lifespan, price, etc., and for this purpose, various semiconductor materials,
Manufacturing technology has been developed and it is widely used in various lamps, numeric display devices, light sources for optoelectronics, etc. LEDs are often used as a single element depending on the application, but especially when manufacturing light emitting display devices such as numbers and letters with LEDs,
So-called arranging multiple LEDs on the same board
The most common method is to fabricate it as an LED array. No matter what field you use LEDs in, that is, when you use them as a single element,
Furthermore, even when used as an array, it is of course desirable that the luminous efficiency be high. However, it has been found that LED arrays obtained by conventional methods have important problems that reduce luminous efficiency.

The above-mentioned problems with this conventional LED array will be explained using the following specific example.

Conventionally, for example, when attempting to manufacture a red LED array using GaAlAs crystal, the following method has been adopted. As the cross-sectional structure is shown in FIG. A p-type GaAlAs crystal layer 3 designed by the growth method is formed. The pn junction formed by this n-type GaAlAs layer 2 and p-type GaAlAs layer 3 becomes the main light emitting region of the LED, but it is better to obtain this pn junction by liquid phase growth than the pn junction obtained by diffusion method. This is because the luminous efficiency is also high.

Now, in order to manufacture an LED array using this crystal, the p-type GaAlAs layer 3 on the light emitting surface side must be electrically isolated. Conventionally, as shown in FIG. 1b, which shows the cross-sectional structure after separation,
After depositing an insulating film 5 such as SiO ₂ , a window of a predetermined size is opened and n-type impurities such as Se and Te are selectively diffused through the window to form an n-type diffusion region that reaches the n-type growth layer 2 . 4 is formed. This will separate the areas that will become individual LEDs into islands.

As can be easily seen from Figure 1, from the p-type surface to the n
When the type impurity diffuses, it diffuses not only in the depth direction but also in the lateral direction, so the width B of the region that will later become the light extraction window is determined by the liquid phase growth, which is the important light emitting surface. As a result, the structure is inevitably much narrower than the width A of the pn junction region thus formed. Therefore, although the pn junction area of liquid phase growth, which has good luminous efficiency and is parallel to the plane of the light extraction window and makes it easy to extract light, is wide, the window that extracts the light to the outside is small. As a result, the luminous efficiency was reduced. In addition, the pn junction formed by diffusion itself has poor luminous efficiency and is in a state where it is difficult to extract light.

In this conventional LED array, the smaller the size of the individual LEDs and the shorter the distance between the LEDs, the more
In other words, the higher the degree of integration, the more the above-mentioned luminous efficiency decreases.

The purpose of the present invention is to solve the problems of conventional LEDs,
In other words, the object is to eliminate the causes of decreasing luminous efficiency and provide an LED array with high luminous efficiency.

An embodiment of the present invention will be described in detail using a GaAlAs red LED array as an example.

In the present invention, the pn junction region, which is the main light emitting region, is formed by liquid phase growth, as in the conventional method. That is, the cross-sectional structure shown in FIG. 2a, obtained by the same method as in FIG. 1a, is used as a crystal plate for manufacturing an LED array.
In order to configure an LED array on this substrate, each LED in the array must be electrically isolated, but the LED array of the present invention can be obtained by the following manufacturing process. . In order to make it easier to understand the present invention, this process is based on an example in which the LED array is arranged in one direction.

From the surface of the crystal plate with the cross-sectional structure shown in Figure 2a,
Selectively diffuse n-type impurities such as Se and Te.
The n-type GaAlAs region 4 formed by the diffusion is made to reach the n-type GaAlAs layer 2 obtained by the liquid phase growth method. The diffusion region 4 seen from the substrate surface is the LED as shown in Figure 2b.
Leaving region 3 where the
It is formed in a region where a metal electrode for ohmic contact with the layer is arranged (a region from which light is not extracted). Thereafter, an insulating film of SiO ₂ , Si ₃ N ₄ or the like is formed on the diffusion region 4 so as to cover the pn junction formed by diffusion exposed on the surface. After that, in order to electrically isolate each LED in the LED array, instead of using the conventional diffusion method, we selected a p-type GaAlAs liquid phase growth layer 3, whose surface structure is shown in Figure 2c. Generally n-type
The cut region 6 is removed so as to reach the GaAlAs liquid phase growth layer 2 and partially cuts into the n-type diffusion region 4. For selective removal of the p-type GaAlAs growth layer, chemical etching is usually used, but other physical and chemical methods such as sputtering may also be used. By doing this, the cross-sectional view in the X-X' direction of Figure 2c has a structure in which the regions 3 that become each LED are electrically isolated, as shown in Figure 2c-1. . In other words, the light emitting area of the pn junction obtained by the liquid phase growth method, which has high luminous efficiency, and the area of the light extraction window are almost equal, and the pn junction obtained by the diffusion method, which has low luminous efficiency, has a second As can be seen from Figure 2 c-2, which is a cross-sectional view in the Y-Y′ direction of Figure c,
Only a small amount remains in the area where the metal electrode for ohmic contact with the p-type GaAlAs layer is placed. Figure 2 c-3 is Figure 2 c-
FIG. 3 is a cross-sectional view in the X' direction. Figure 2 d is Figure 2 c
This is an example of a surface layout configuration diagram completed by forming a metal electrode 7 for ohmic contact on a p-type GaAlAs growth layer of an LED array.

In this way, in the LED array according to the present invention, the actual light emitting area (that is, the pn junction area obtained by the highly efficient liquid phase growth method) and the light extraction area are almost the same, so it is not possible to emit light like the conventional one. Loss can be extremely reduced, resulting in
This makes it possible to increase the luminous efficiency of the LED array. Moreover, the area of the extra pn junction formed by the diffusion method is small, so each LED
Even if the light extraction area is the same, the junction area is smaller than that of conventional LEDs, so current density can be increased, and the light emission intensity also increases.

As mentioned above, the LED array shown in FIG. 2 according to the present invention has a much higher luminous efficiency than the conventional LED array, but there still remains some pn junction region due to the diffusion method with low luminous efficiency. There is.
For the purpose of further clarifying the invention, FIG.
An embodiment for further improving the luminous efficiency of the LED array will be described based on FIG. 3.

N-type impurities such as Se and Te are selectively diffused from the surface of the substrate as shown in FIG. 2a to the top of the p-type GaAlAs growth layer 3 as shown in the plan view in FIG. A plurality of n-type diffusion regions 4 are formed. The diffusion depth is set to reach the n-type GaAlAs growth layer 2. The size, shape, and arrangement of this n-type diffusion region 4 are determined by the fact that a metal electrode for ohmic contact will be formed on the p-type GaAlAs growth layer 3, which will finally become the light emitting surface. The decision will be made accordingly.

After an insulating layer 5 of SiO ₂ , Si ₃ N ₄ or the like is formed to cover the n-type diffusion region 4, the above-mentioned cut region 6 is provided. This cut area 6 is shown in Figure 3b.
As shown in the plan view after completion of the LED array, the LED array is provided so as to extend over the entire surface except for the region 3 that will become the light emitting surface and the electrode 7, and to reach the depth of the n-type GaAlAs layer 2.

Therefore, as can be understood from FIG. 3c, which is a cross-sectional view of one LED in the LED array (a cross-sectional view along the Y-Y' direction in FIG. 3b), the LED is formed by diffusion. Since the pn junction exists only in the portion below the electrode that connects the electrode 7 and the light emitting region 3, the luminous efficiency and luminous intensity are further improved compared to the LED array having the structure shown in FIG.

The present invention has been described above using a GaAlAs red LED array as an example, but LEDs using other - group compound semiconductors or - group compound semiconductors may also be used.
Of course, it can also be applied to arrays. Also,
There is no problem even if the LED array has a conduction type completely opposite to that shown in Figure 2. Furthermore, although the cut region is formed before the formation of the ohmic electrode on the surface in the example shown in FIG. 2, it may be formed after the formation of the ohmic electrode. Furthermore, it goes without saying that a method of pouring synthetic resin or the like into the cut area may also be used.

[Brief explanation of the drawing]

Figure 1a shows n-type GaAlAs on an n-type GaAs crystal substrate.
FIG. 2 is a cross-sectional structural diagram of a crystal plate in which a p-type GaAlAs growth layer is obtained by liquid phase growth. Figure 1b shows the conventional
Cross-sectional structure diagram of GaAlAs LED array. Figure 2 a is the same as Figure 1 a, with an n-type GaAs crystal substrate and an n-type GaAs crystal substrate.
FIG. 2 is a cross-sectional view of a crystal plate in which a GaAlAs and p-type GaAlAs growth layer is obtained by liquid phase growth. FIG. 2b is a plan view of the surface of FIG. 2a after selectively diffusing n-type impurities according to the present invention. FIG. 2c is a plan view of the GaAlAs LED array after the notch region according to the present invention is formed, and FIG.
Cross-sectional views in the X' direction, c-2 in the Y-Y' direction, and c-3 in the -' direction. FIG. 2d is a plan view of a completed GaAlAs LED array in which metal electrodes are provided after the notch region is formed according to the present invention. FIG. 3a is selectively n from the surface of FIG. 2a according to the present invention.
FIG. 2 is a plan view of a substrate in which a type impurity is diffused to form a diffusion region, viewed from the surface. FIG. 3b is a plan view of a completed GaAlAs LED array with cut regions formed according to the present invention. FIG. 3c is a cross-sectional view taken along YY' direction of FIG. 3b. DESCRIPTION OF SYMBOLS 1... n-type GaAs substrate; 2... n-type GaAlAs crystal layer; 3... p-type GaAlAs crystal layer; 4... n-type diffusion region; 5... insulating film; 6... notch region; 7... electrode.

Claims (1)

[Claims] 1. By forming a growth layer having a first conductivity type by liquid phase growth on a semiconductor crystal, and a growth layer having a second conductivity type opposite to the first conductivity type by subsequent liquid phase growth. In a light emitting diode array in which a plurality of light emitting diodes are arranged on a semiconductor substrate having a pn junction, a metal electrode region is arranged to provide ohmic contact with the light emitting surface of each light emitting diode constituting the light emitting diode array. A region of the second growth layer corresponding approximately to the region of the growth layer having the first conductivity type is converted by selective diffusion to the same conductivity type as the growth layer having the first conductivity type, and a region of the second growth layer that becomes the light emitting surface of each light emitting diode is A light emitting diode array characterized in that the second growth layer in other parts is removed, leaving only the layer region and the second growth layer region whose conductivity type has been converted substantially corresponding to the metal electrode region. .