DE2429189A1 - PROCESS FOR MANUFACTURING A SEMICONDUCTOR PHOTOCATHOD INTENDED FOR TRANSMISSION OPERATION - Google Patents

Description

BLUMBACH -WESER BERGEN & KRAMER

PATENT LAWYERS IN WIESBADEN AND MUNICH

DlPL-ING. P. G. BLUMBACH-DIPL-PHYS. DR. W. WESER DIPL-ING. DR. JUR. P. BERGEN DIPL-ING. R. KRAMER

WIESBADEN · SONNENBERGER STRASSE 43 · TEL. (06121) 562943, 561998 MÖNCHEN

Ftnrrarnatriu TV C -'- ". T / r ·" ":.

-Jiizuuka, Japan ί-'ara I

Method for the production of an i ialbleitfc i-fotokaüiotle_

! Ue invention relates to a method for producing a iialconductor photocathode intended for operation in transmitted light.

If the surface of ρ-conducting semiconductor crystals looks like like iliziuni or C: allium arsenic! and other suitable TII-V compound semiconductors are cleaned and their Klektro · affinities by activating with oesiuir or aosiuii; and Oxygen is made small, the electrons are that are excited by incident light in the semiconductor, emitted into a vacuum. Semiconductor photocathodes of this type have over a wide range of waves a comparative constant Speirtralempfmdlithki.it on; also work they are highly efficient and with small = ounkelstr ..) ni.

409883/0944

2429139

Per photocathode type working in transmitted light mode, for example used in image pickup tubes. In this ■ all are thin areas or zones that form i ^ otoelectrons, necessary to prevent the electrons excited by light from reaching the emission surface during the infusion attenuated or deleted. Crystallinity must also be improved in order to increase the diffusion path length. Previously, gallium arsenide crystals were made in thin layers grown on transparent, insulating substrates such as sapphire. Because of the pronounced difference of the crystal structures of the substrate and the gallium arsenide, the bad crystal was grown as soon as the layer patches became less. It was therefore necessary to make the layer considerably thicker than the diffusion path length of the electrons, to remedy this deficiency. This resulted in a drop in photoelectric sensitivity.

Furthermore, a method is known in which a single crystal substrate from gallium phosphide with the same crystal structure

409883 / Ü944

2429183

and a wide forbidden band is used, and at to overcome the citter constant difference this substrate a gallium arsenic phosphor transition layer and then a gallium arsenide thin layer in which ^ otoelectrons be formed, let grow up,! "- och have the / otocathodes obtained by this process the main disadvantage that their light-sensitive zones are decidedly narrower because the short ones are very long of the incident light are absorbed by the gallium phosphide and the gallium arsenic phosphor layers.

It has already been proposed to grow gallium arsenide on germanium, which has a similar crystal structure and small lattice constant deviation, and this method still lacked the need to reduce the absorption of incident light by making the substrate very thin because the forbidden band of germanium T ₁ represents 66 electron volts, and is substantially narrower than the forbidden band of gallium arsenide.

409883/0944

The object of the invention is to remedy these and other known disadvantages.

To solve the problem, the invention is based on a method of the type mentioned at the beginning and is characterized by

A. Growing a semiconductor crystal thin film having photoelectron emission properties on a substrate whose crystal structure is the same as that of the semiconductor crystal or is similar

B. Growing a transparent protective layer on the thin film and

C. Removing at least a portion of the substrate to thereby exposing a portion of the thin film for use as a photoelectron emitting surface.

The thin film can be appropriately doped so that it is p, or becomes strongly p-conductive.

An important feature of the invention is in the partial

409883/0944

or complete removal of the substrate from the crystal layer grown on the substrate, whereby a photoelectron-emitting surface is formed in the layer areas exposed in this way. If the substrate is only partially removed, the remaining parts provide additional mechanical strength.

The substrate may advantageously be non-transparent because part of it is removed to form a surface area of the layer so that the photoelectron emitting surface is formed.

In one application, the layer with the exposed Surface, the remaining substrate part and the protective layer in connection with a fluorescent screen or a fluorescent surface over the designated exposed surface, Be acceleration electrodes between the exposed Surface and the screen, a receptacle device therefor, a device for projecting an image

409883/0944

can be used on the protective layer and photoelectron emission on the screen.

Another advantage of the invention is that the invention is easy to carry out and the resulting device is reliable and efficient. The layered crystal can be of any thickness desired.

The invention will be described in detail below in conjunction with the accompanying drawings and furthermore Features and benefits received. The drawings show:

IA, IB and IC show an embodiment of various

Stages in the production of the component according to the invention,

Fig. 2 the application of the according to the invention

according to the method produced component in a television camera.

409883/0944

It is now the production process in connection with the Pig. IA, IB and IC are described. Layer 2 will grown or grown on a substrate 1. The substrate 1 can be made of a material with the same or a similar crystal structure as that of the layer, which can be a semiconductor crystal, in which ITbto electrons are formed. The layer 2 can be made of the vapor phase, the liquid phase or by vapor deposition using a suitable method can be grown on the substrate 1 in a vacuum. After the crystal is grown on the substrate, like FIG. 3 shows a protective layer 3 made of a suitable one; transparent material allowed to grow or otherwise attached to the layer 2 appended. Then at least part of the substrate 1 (FIG. IC) is removed, for example by chemical etching. It is possible, to increase the mechanical strength of the photocathode produced by this method by a part of the substrate 1, the is represented by the broken lines 1 *, is left to stand.

409883/0944

In Fig. 2, the photocathode obtained according to the method just described is shown and within a cylindris small, airtight vessel that forms a picture tube, shown. The surface of the semiconductor crystal layer 2, which by partial or complete removal of the substrate 1 has been exposed is arranged to face a fluorescent surface or fluorescent as shown Screen 5 is opposite. A plurality of acceleration electrodes are located between the exposed surface and the screen 6, 6 ... arranged. The container or vessel 4 can be connected to a high vacuum pump system so that the Gas in the vessel is evacuated. The surface of the crystal 2 can be cleaned and in a known manner with cesium or cesium and oxygen are activated. The vessel can then be separated from the pump system and sealed airtight. from of the lens 7, an optical image can be projected onto the photocathode and thus an electron image onto the fluorescent screen 5.

409883/0944

As already described above, according to the method, a layer 1 is removed on which a semiconductor crystal layer, The photoelectrons emitted had been allowed to grow, thereby creating a photoelectron emitting surface in the through removing the substrate to form exposed area. Therefore, any non-transparent substrate material can be used Material to be used. Even if you have materials whose crystal structure is the same or similar to the structure of the semiconductor crystal 2 and whose lattice constants are closely matched to one another are used, it is possible to use the semiconductor crystal 2 to make it extremely thin and still achieve good crystallinity. For example, if the photoelectron emitting semiconductor 2 is a gallium arsenide semiconductor, the materials, which meet the conditions just described, be gallium arsenide, zinc selenide, or germanium. It can other materials for the substrate 1 and the crystal 2 can be used, which depends on the type of component and the desired functions.

409 8 83/09 44

ίο

After removing the substrate 1, the protective layer 3 carries the crystal 2 and can protect the crystal layer 2 by it covers the surface of the same during the removal of substrate 1, which is carried out, for example, by etching. One suitable thick layer with a suitable refractive index means that less incident light is reflected. Because after the Growing the layer 2 on top of the layer 3 is formed, it is possible to use any transparent material without restrictions with regard to properties such as crystal structure and lattice constant. Pur the range of the transmission wavelength it is sufficient to include the light-sensitive zone of the thin-film crystal 2. Layer 3 can be made from Material such as silicon dioxide, silicon monoxide, silicon nitride and aluminum oxide. Although the photosensitive Zone of crystal 2 is somewhat narrower in the case of gallium arsenide, it is also possible. Material such as Use gallium phosphide and zinc selenide. It is also possible to use a plurality of layers from the aforementioned different materials to form.

409883 / 094A

The substrate 1 can be partially or completely removed by mechanical grinding. Because of this, however, the crystal 2 is easily damaged, another preferred method is chemical etching. It can be different materials for the crystal 2 and the substrate 1 are used, so that the conductive and / or dopant concentrations of the Crystal and the substrate change and differences in the etching speeds have the effect that the Substrate 1 is removed alone and the crystal 2 remains essentially undamaged. Even in the event that only one Part of the substrate 1 is removed, as shown by the broken lines 1 * in Fig. IC the remaining part is covered with a substance that is resistant to the etching solution and is therefore not etched. A suitable etching solution can be used so that the etching speed of the substrate 1 and the crystal 2 is low. It is also possible to determine the differences between these etching speeds by local irradiation or, if required, to enlarge by electrolytic etching.

409883/09 44

It can also be desirable for the same applications be that the electron-emitting surface of the layer 2 is strongly p-conductive. However, a heavily p-type zone becomes in usually etched at a faster rate than before n-type or a lightly doped zone. It is also possible to grow a lightly doped crystal 2 on the substrate 1 and after removing the substrate, diffusing p-type dopants into the crystal 2 so that the layer 2 is strong becomes p-conductive.

An embodiment will now be described. in the In the case of this exemplary embodiment, the substrate was produced as gallium arsenide, its FLOO) surface or (100) -B surface was mirrored by mechanical grinding or polishing, for example. The substrate 1 was with a

3: 1: 1 solution from H_SO., H-O and HO etched, then

2 4 2 2 2

see and dried. Then the substrate was in exposed to a hydrogen atmosphere in a liquid phase cultivator. One to a prescribed dopant -

409883/0944

amount and gallium arsenide in the amount that was found at the growth start temperature saturate, added gallium solution, was heated to the growth start temperature, in contact brought with the substrate 1 and then cooled until a crystal 2 of the desired thickness was grown on the substrate 1. Then the substrate 1 and the solution were separated and cooled to room temperature. The dopants became like this doped that their concentration in crystal 2 in the case of

18 19 2

Zinc about 10 to 5 χ 10 atoms / cm and in the case of

17 18 2

Silicon or germanium was around Io to Io atoms / cm. The crystal layer 2 is preferably between a few micrometers to several tens of micrometers thick. The substrate and the semiconductor crystal 2 grown thereon in the manner described above were then placed in a furnace for heating. Argon gas, which had previously been passed through an ethyltriethyloxysilane solution and contained its vapors, was fed to the furnace. After heating to about 700 ^° C., a protective layer 3 was precipitated on the silicon dioxide crystal 2 in the furnace by pyrolysis.

■ 4 09883/0944

The treatment time was sufficient to be able to form a transparent and thick layer 3. The surface of the layer 3 can, as required, e.g. B. be attached to a glass plate with wax. If part of the substrate is to remain, this part is also covered with wax. Then the assembly was immersed in a known, above-described etching solution to remove the parts of the substrate 1 and dissolve. Further, when an η-conductive substrate 1 is used, it is possible to rapidly dissolve only the substrate by irradiating. Thereafter, the device or component produced was washed in water and dried. Peripherally ohmic contact electrodes were placed to form cathodes. ^: Then the device or the component was, for example, placed in a vessel, as shown in FIG. 2, and the surface of the crystal 2 was then activated with cesium or cesium and oxygen.

Regarding the example given above, it should be noted

409883/0944

that the etching process, the crystal growth, the The substrate 1 is polished and the protective layer 3 itself is grown on, all according to known methods walk. So little additional equipment is required to carry out the proposed method. Also need the tolerances are not restricted in the usual way, because the substrate material as a material with both transparent and non-transparent properties and the like or the same crystal structures and lattice constants which are closely matched to those of the crystal layer can be selected and the substrate is then removed. The specific procedures applied for each step can be used in any reputable Manufacturing manual and are known to those skilled in the art. As a result, no special operating parameters are required here to be reproduced.

Because according to the proposed method it is possible photoelectron emitting semiconductor crystals on substrates to raise them in crystal structure and terms

409883/0944

the lattice constants are very similar, it is possible to have crystal layers that are essentially thin and have good crystal properties or good crystallinity fcrystallinity) exhibit. As a result, high-performance potocathodes for transmitted light operation can be manufactured.

In the foregoing description, an exemplary embodiment has been used in application of the »proposed procedure. Numerous modifications will be made to those skilled in the art Modifications are obvious without wiping away from the content according to the method.

409883/0944

Claims (12)

DlPL-ING. R. KRAMER MÖNCHEN 17th PATENT CLAIMS Process for producing a semiconductor photocathode intended for transmitted light operation, marked by A. growing a semiconductor crystal thin film having photoelectron emission properties on a substrate, whose crystal structure is the same or similar to that of the semiconductor crystal, B. Growing a transparent protective layer on the thin film and C. Removing at least a portion of the substrate, thereby forming a portion of the thin film for use as a expose photoelectron emitting surface. 2. The method according to claim 1, characterized. 40 9 8 83/0944 that the thin film from the vapor phase, from liquid Phase is grown or by evaporation in a vacuum. 3. The method according to claim 1, characterized in that the substrate is removed by etching, wherein the The substrate is etched at a faster rate than the thin film. 4. The method according to claim 1, characterized in that that the substrate is completely removed. 5. The method according to claim 1, characterized in that a non-transparent material for the substrate is used, the lattice constant of which is closely matched to that of the crystalline thin film. 409883/094 6. The method according to claim 1, characterized in that that for the semiconductor thin film gallium arsenide and gallium arsenide, gallium phosphide, zinc selenide and / or germanium can be used for the substrate. 7. The method according to claim 2, characterized in that that silicon dioxide, silicon monoxide, silicon nitride and / or aluminum oxide are used for the protective layer. 8. The method according to claim 1, characterized in that that the semiconductor is grown thinly between a few micrometers and several micrometers corner. . 9. Semiconductor component, characterized by 40988 3/0944 Λ. a layer grown on a substrate with the same or a similar crystal structure, B. a transparent protective layer on the layer and C. the further feature that the layer passes through on the side opposite the transparent layer partial or complete removal of the substrate to form a surface for photoelectron emission is exposed. 10. Semiconductor component according to claim 9, characterized in that the layer made of gallium arsenide and the substrate Gallium arsenide, gallium phosphide, zinc selenide and / or germanium is built up, that the layer is between a few micrometers and several tens of micrometers sick and that the protective layer is composed of silicon monoxide, silicon dioxide and silicon nitride and / or aluminum oxide. 409883/0944 242S183 11. Semiconductor component according to claim 1C, characterized, that the layer is strongly p-conductive. 12. Semiconductor component according to claim 9, characterized in that that a fluorescent screen faces the exposed surface of the layer, that acceleration electrodes are placed between the exposed surface and the fluorescent screen are, that substrate, layer, protective layer, fluorescent screen and electrode are housed in one container are and that means for projecting an image through the protective layer onto the layer is provided to emit photoelectrons as the image on the screen. A0S883 / Ü944 Blank page