JPS584835B2 - GaP green light emitting display device - Google Patents

Description

[Detailed description of the invention] This invention relates to improvements in GaP green light emitting displays.

Conventionally, monolithic semiconductor light emitting display devices have been manufactured by various methods, and for example, a planar type red light emitting display device using GaAs1-xPx has already been widely applied.

On the other hand, since red light strongly irritates the human eye, green semiconductor light emitting display devices are being developed in various places.

However, materials that emit green light with high efficiency are currently limited to GaP, and the reality is that GaP green light emitting display devices have not yet achieved sufficient contrast.

The reason for this will be explained using FIG. FIG. 1 schematically shows a planar monolithic light emitting display device using GaP crystal, in which a diffusion mask 2 with selective windows is provided on an n-type GaP substrate 1 containing sulfur and nitrogen to prevent zinc diffusion. Then, a P-type layer 3 was formed.

With this configuration, by passing a forward bias current through the pn junction, green light A is emitted from the pn junction surface.

However, the light from the outside is exposed to the diffusion mask 20 outside the light emitting area.
The reflected lights B and C reflected by the surface or the surface of the GaP substrate 1 and entering the human eye are considerably large.

Furthermore, since the GaP crystal is transparent, the reflected light D that enters the substrate 1, is reflected on the back surface, and comes out cannot be ignored.

That is, since the reflected lights B, C, and D are thicker than the desired green light A, the contrast between the light-emitting part and the non-light-emitting part is very poor, and there is a problem that the display device lacks clarity and resolution. there were.

This invention has been made in view of the above points, and provides a GaP green light-emitting display device that increases the contrast between the light-emitting part and the non-light-emitting part, and improves the clarity and resolution of the display device. .

The gist of the invention is that in a GaP green light emitting display device,
The contrast is improved by covering the surface of the GaP substrate other than the light emitting part with a silicon nitride film of 1600 to 2400 A, and by making the back surface of the GaP substrate a rough surface and depositing a light absorber layer on this surface.

A silicon nitride film is normally used as a diffusion mask when selectively diffusing impurities into a GaP substrate, but by forming this mask to the above-mentioned thickness and leaving it as it is on the surface of the non-emitting part, green light can be significantly reduced. This results in a significant improvement in contrast.

The reason for this will be explained below. When a GaP substrate is coated with a mask, the conditions to minimize reflection of external light are as follows:
If the refractive index of the P substrate is ns and the refractive index of the mask is n, then n
It is given by s=n2.

For green light, ns=3.5, so n=1.
The optimum condition is about 9.

A silicon nitride film can be formed at a temperature of 200 to 850°C to have a refractive index of about 1.9. Therefore, if a silicon nitride film is used as a diffusion mask and its thickness is set within a predetermined range, green light can be produced. This means that the reflection can be reduced to almost zero.

Figure 2 shows the thickness of the silicon nitride film and the green reflected light when a silicon nitride film is coated on the front surface of the GaP substrate, a light absorber layer is deposited on the back surface, and external light is applied through a green filter. This is data that measures the strength of the relationship.

Note that the intensity of green reflected light is expressed as a ratio to the intensity of external light that has passed through the green filter.

Further, the thickness of the silicon nitride film is limited to a range that can be practically used as a selective diffusion mask.

As is clear from this data, green reflected light can be effectively suppressed by selecting the thickness of the silicon nitride film in the range of 1600 to 2400 Å.

Next, an embodiment of the present invention will be described with reference to FIGS. 3 a to 3 e and FIG. 4.

FIG. 3 shows the wafer processing process. First, an n-type GaP substrate 11 containing sulfur and nitrogen is used, and a
A silicon nitride film 12 of 1600 to 2400 A is coated by a so-called CVD method in which silane gas and ammonia gas are reacted at 0 to 800° C. (a).

Next, using a photoresist (not shown) as a mask, the silicon nitride film 12 is selectively etched by Freon plasma etching to expose the surface of the GaP substrate 11 at a predetermined position (b).

Zinc is then diffused using the remaining silicon nitride film 12 as a selective diffusion mask, and the p-type layers 13 and 1 are approximately 5 μm deep.
31,132 (c).

After polishing the back surface of the GaP substrate 11 by 5 μm or more, a gold-beryllium (1ωt%) alloy and gold are deposited on the surface, and this is patterned to form a p-type layer 13 on the surface of the p-type layer 13.
Side electrodes 14, 141, 142 are formed (d).

In order to keep the back surface of the polished GaP substrate 11 rough,
It is better not to perform acid treatment after polishing.

Next, an amorphous or polycrystalline silicon layer 15 with a thickness of 0.5 to 1.5 μm is deposited on the back surface of the GaP substrate 11, followed by a gold-silicon (2ωt%) alloy layer 16, A multilayer n-side electrode 18 is formed by continuously depositing a gold layer 17 (e).

This n-side electrode 18 also serves as a light absorber layer, and by making the back surface of the substrate rough, it becomes an effective light absorber layer.

After heat treatment at 500° C. for 10 minutes, the chip is cut out and fixed on the stem 19 using gold-epoxy paste as shown in FIG. , 202 and the p-side electrode 14
A bonding connection is made between them using gold wires 21, 211, and 212, and a green filter 22 is installed on top to complete the display device.

The n-side lead 23 is integrally connected to the stem 19 and electrically connected to the n-side electrode 18 of the element.

With this structure, by applying a forward bias between the leads 20 and 23, green light is emitted at the junction surface between the p-type layer 13 and the substrate 11, and a desired pattern is displayed.

In this case, the light from the light emitting section passes through the green filter 22 and is sensed by the human eye.

On the other hand, outside light entering the device through the green filter 22 is filtered through the silicon nitride film 12 by the above-mentioned Kamiyama in the non-light emitting region.
It will not be reflected.

Then, the GaP substrate 1 is passed through this silicon nitride film 12.
Since the n-side electrode 18 having a multilayer structure provided on the rough back surface acts as a good light absorber layer, the light that has traveled inside the device 1 is not reflected back from the back surface.

Therefore, the non-light-emitting area becomes almost completely black, and a green light-emitting display with extremely high clarity and resolution is performed.

Note that this invention is not limited to the above embodiments.

For example, in the embodiment, a green filter is installed on the front side of the element, but as shown in FIG. 5, after mounting a face on a stem and bonding, the entire element may be molded with green transparent resin 24.

Resin molding is easier to work with than fixing the filter.
Moreover, it has the advantage of being resistant to vibration.

In addition, in the example, a laminated film consisting of a silicon layer, a gold-silicon alloy layer, and a gold layer was used as the n-side electrode to function as a light absorber, but even without the silicon layer, it is sufficient to have a light absorber layer. Work as.

Furthermore, a germanium layer, a gold-germanium alloy layer,
A laminated film made of a gold layer may be used as an n-side electrode that also serves as a light absorber.

In addition, the present invention can be modified and implemented in various ways without departing from its spirit.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the contrast between the light emitting part and the non-light emitting part of a GaP green light emitting display device, FIG. 2 is a diagram showing experimental data for explaining the effects of this invention, and FIGS.
e is a diagram for explaining the wafer processing step of an embodiment of the present invention, FIG. Figure 5 shows Ga of another embodiment of this invention.
FIG. 3 is a diagram showing a P green light emitting display device. 11... N-type GaP substrate, 12... Silicon nitride film, 13, 131, 132... P-type layer, 14, 141,
142... p-side electrode, 15... silicon layer, 16...
...Gold-silicon alloy layer, 17...Gold layer, 18...
n-side electrode (light absorber layer), 19... stem, 20, 2
0,202...p side lead, 21,211,212
... Gold wire, 22 ... Green filter, 23 ... N-side lead 24 ... Green transparent resin.

Claims (1)

[Claims] 1 In a device that forms a Pn junction on a GaP substrate to perform a green light emitting display, the surface of the substrate other than the light emitting part is
1. A GaP green light emitting display device comprising a substrate covered with a silicon nitride film of ~2400A, the back surface of the substrate being made rough, and a light absorbing layer being deposited on this surface.