JPH0441516B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use Visible light-emitting diodes (LEDs) are widely used as pilot lamps and display elements such as numeric display elements and level indicators. Especially in the field of display, red,
Three-color LEDs, yellow and green, are often used.
GaP green LEDs, which are formed by sequentially growing n-type and p-type epitaxial layers on a gallium phosphide (hereinafter abbreviated as GaP) substrate, are visible along with GaP red LEDs.
It occupies a central position among LEDs. The present invention provides a GaP green LED suitable for the above display element.
Regarding.

Conventional configuration and its problems GaP green LEDs contain nitrogen (N) as the emission center and are yellow-green with a peak emission wavelength of 565 nm.
There are two types: LED and pure green LED, which does not contain nitrogen and has a peak emission wavelength of 555 nm. Both of these structures are formed by sequentially growing n-type and p-type epitaxial layers on an n-type GaP substrate.

GaP substrates are generally sliced into 111 planes, and these planes include an A plane (gallium plane) and a B plane (phosphorus plane). The A-plane is chemically stable and difficult to be etched, and when an epitaxial layer is formed on the A-plane, it is difficult to dope impurities into the epitaxial layer. Therefore, the epitaxial layer is usually formed on the B-plane. will grow upwards. The back surface of the substrate of the GaP LED formed as a result is the A side.

FIG. 1 is a diagram showing the cross-sectional structure of a conventional GaP green LED having such a structure. An n-type GaP epitaxial layer 2 is grown on the B side of an n-type GaP substrate 1, and then a It has a structure in which a p-type GaP epitaxial layer 3 is grown, and a GaP green LED element formed by providing electrodes 4 and 5 is fixed to a support 6 such as a stem. By the way, as mentioned above, the n-type and p-type epitaxial layers are formed on the B side of the n-type GaP substrate 1, while the A side, which is the back side of the n-type GaP substrate of the GaP green LED, is formed on the B side of the n-type GaP substrate 1. In order to make the thickness of the GaP substrate 1 uniform and to increase the light reflectance on this surface, it is polished to a mirror surface. and
In a GaP green LED, the light emitted near the pn junction and emitted to the outside is
The light component is roughly divided into a light component that is directly emitted to the outside, as shown by , and a light component that is once reflected on the A surface and emitted to the outside, as shown by Y in the figure.

The light emission of GaP pure green LEDs is close to the GaP bandgap, and has large internal absorption. Therefore,
Most of the light that is multiple-reflected within the GaP pure green LED is absorbed, and the light component Y that is reflected once on the A plane and emitted to the outside as described above is also largely absorbed. For this reason, traditional GaP pure green LEDs
It was not possible to obtain high luminous output.

Similar problems also occurred with GaP yellow-green LEDs.

Purpose of the Invention The present invention reduces the amount of light emitted inside a GaP green LED by internal absorption of the light component that is emitted to the outside through internal reflection. The purpose of this invention is to provide a method for manufacturing this.

Structure of the invention The present invention serves as a starting material for GaP green LEDs.
When the A-side of a GaP substrate, which is difficult to etch, is etched with aqua regia, etch pits and tortoiseshell-like irregularities occur on the etched surface due to crystal defects.
In other words, etching was previously considered difficult.
This was done based on the confirmation that surface A of a GaP substrate could be textured, and the structure of a GaP green LED was created on the 111B surface of an n-type GaP substrate, which is the starting material for a GaP green LED. n-type all over
A GaP epitaxial layer is formed, a p-type GaP epitaxial layer is further formed thereon, and the GaP After forming n-type and p-type GaP epitaxial layers on the 111B surface of an n-type GaP substrate prepared as a starting material for a green LED, etching the back side A of the n-type GaP substrate with aqua regia, Same n type
A method is adopted in which the back side of the GaP substrate is made to have an uneven surface, and then this substrate is subdivided into chips so that the pn junction surface and the back surface of the substrate have approximately the same area. In this method, the back side (A
For GaP green LEDs with a textured surface (surface),
The light emitted inside becomes diffusely reflected on the back surface, and light is also emitted to the outside from the side of the GaP green LED element. Overall, the amount of light absorbed inside the board is reduced, resulting in high light output. By the way.

DESCRIPTION OF THE EMBODIMENTS FIG. 2 is a sectional view showing an embodiment of the GaP green LED of the present invention, and the basic structure is the same as the conventional one shown in FIG.

However, as shown, GaP green color
Since the back surface (Side A) of the n-type GaP substrate, which is the surface to be bonded to the support 6 of the LED element, is an uneven surface, the light emitted internally that is reflected from this surface is This unevenness causes diffuse reflection. In other words, the light reflected from the back surface of the n-type GaP substrate is composed of the light component Y emitted to the outside from the p-type epitaxial layer surface (one surface) and this LED.
It is divided into a light component Z which is emitted to the outside from the side surface of the element itself, and most of it is occupied by the light component Z. The passage distance inside the element of the light component Z emitted to the outside from this side surface is shorter than that of the light component Y, and therefore the amount of internal absorption is reduced. In other words, the back surface (A side) of the n-type GaP substrate
Of the light components reflected by the LED, the amount of light emitted to the outside of the device increases, improving the light emitting output characteristics of the GaP green LED compared to conventional structures.

By the way, the present invention having such a structure
The GaP green LED is formed by the method described below. First, n-type and p-type GaP epitaxial layers are sequentially grown in liquid phase on the 111B surface of an n-type GaP substrate. Next, the back side A of this epitaxially grown GaP substrate is removed by mechanical polishing to a predetermined thickness, and only this polished surface is exposed and etched with aqua regia for several minutes. As a result of this etching process, the back side A of the substrate becomes an uneven surface as shown in FIG. After this, a GaP green LED having the structure shown in FIG. 2 is formed through the formation of electrodes and the adhesion of the element to the support.

In order to confirm the effects of the present invention explained above, Figure 3 shows a GaP pure green LED with a conventional structure formed by mirror polishing the back surface of an n-type GaP substrate, and a GaP pure green LED with an uneven structure formed by etching the back surface of the n-type GaP substrate with aqua regia. FIG. 3 is a diagram showing a comparison of light emitting outputs of processed and formed GaP pure green LEDs of the present invention.

As shown in the figure, according to the present invention, the light emission output is approximately 20% larger than that of the conventional structure, and a high light emission output is achieved.

Note that similar results were obtained when the present invention was applied to a GaP yellow-green LED.

Effects of the Invention According to the present invention, it is possible to increase the light emitting output of GaP green LEDs without making any major changes to the basic structure or basic manufacturing process of GaP green LEDs, and the display field of GaP LEDs can be improved. This has the effect of expanding the scope of application.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the structure of a conventional GaP green LED in which the back surface of an n-type GaP substrate is polished to a mirror surface, and Figure 2 is a cross-sectional view showing the structure of a conventional GaP green LED in which the back surface of an n-type GaP substrate is made uneven by aqua regia etching. FIG. 3 is a cross-sectional view showing the structure of a GaP green LED, and is a diagram showing a comparison of light emitting output between a conventional GaP pure green LED and a GaP pure green LED of the present invention. 1...n-type GaP substrate, 2...n-type GaP epitaxial layer, 3...p-type GaP epitaxial layer, 4
...N-type side electrode, 5...P-type both sides electrode, 6...
Support (stem).

Claims (1)

[Claims] 1 111B surface (phosphorus surface) of n-type gallium phosphide substrate
Above, a pn layer consisting of an n-type gallium phosphide epitaxial layer and a p-type gallium phosphide epitaxial layer.
a step of forming a bond, a step of removing the back side 111A (gallium surface) of the n-type gallium phosphide substrate by mechanical polishing to a predetermined thickness, and then etching it with aqua regia to form an uneven surface; A step of partially forming an electrode on the uneven surface, and dividing the gallium phosphide substrate including the p-n junction into pieces so that the areas of the p-n junction surface and the uneven surface are approximately the same, and forming chips. A method for manufacturing a green light emitting diode, comprising a step of: