CS245592B1 - Target of vidicon pickup tube or another electrooptic converter - Google Patents

Abstract

Multi-layer electrooptical target optical image / el. image, signal, where blocking layers for holes and electrons They are made of alloyed materials elements of the second and third, and fifth and fifth respectively the sixth group of the periodic system and have the width of the forbidden belt at least o 0.001 eV greater than the forbidden width the energy of the layer in which it occurs to photoelectric or induced conductivity.

Description

BACKGROUND OF THE INVENTION The present invention relates to a target for a television sensor tube of the vidicon type and similar electro-optical optical / electrical signal converters.

The essence of these devices is the conversion of the optical image projected onto their input into an image electrical signal at their output, which consists of the electro-optical (e.g. photoelectric) conversion of information carriers (information is transferred from photons to electric charge carriers), the spatio-temporal transformation that results from an optical image of an electrical video signal. Target is a multilayer structure that is deposited on glass or other radiation transmissive backing, or may optionally be self-supporting, in whose individual layers the above processes take place. The basic schematic composition of the target is shown in Fig. 1.

When sensing the accumulation surface of a target by an electron beam under conditions such that the secondary emission coefficient of the accumulation surface is less than 1, an electric field is created in the target, determined by the positive potential of the signal electrode connected to a source whose negative pole is connected to the electron source electron guns). Radiation passing through the signal sleeve to the photoconductive part of the target generates electron-hole pairs.

The charges are separated by an internal field in the target so that the positive charge accumulates on the side of the incident beam. The sensitivity of the element is then dependent on the magnitude of the charge generated and the time of accumulation, and thus depends on minimizing recombination of the holes as they pass from the excitation site to the accumulation surface. Therefore, both sides of the structure are provided with blocking layers which on the signal electrode side prevent back-diffusion of the holes and, on the other hand, on the side of the incident electrons prevent their penetration into the target.

In the case of α-Si: H-based vidicones, a-SiO, α-Si _x Ny, Sb2Sj, AS2Se ^ 5 ^Te y 5 ^and alloys of α-Si: H, n or p type have been used to block the blocking effects (see Fig. 2).

All these materials can be divided into two types:

and - materials with a wider band of prohibited energies than the photoconductive layer itself (see Fig. 2);

b - materials with the same bandwidth of the energy prohibited as the photoconductive layer (see Fig. 3).

In the case of a - the blocking layers are optically well permeable, there is no loss of absorbed radiation, but because they partially block the opposite type of wearers, both types of wearers accumulate at their interface with the photoconductive layer and at the same time increase their recombination.

In the case of b - accumulation, opposite charges do not occur, but due to the same width of the forbidden energy band, partial absorption of radiation already occurs in the blocking layer at the signal electrode and thus the sensitivity of the whole element decreases significantly, especially in the shortwave part of the spectral characteristic.

It has therefore proven necessary to solve a targent structure in which both types of charge at the interface do not accumulate and where appropriate adjusting of the alloy will adjust the dark current so that the inertia is optimal.

The object of the present invention is that the blocking layers for holes and electrons are formed from amorphous materials alloyed with elements of the second and third and fifth and sixth groups of the periodic system and have a band gap of at least 0.001 eV — Greater than the width of the banned band by the photoconductive layer energy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a prior art target composition; FIGS. 2 and 3 are schematically depicted target band models of the prior art; FIG. 4 is a schematic depicted target band model of the present invention; 5 shows a basic schematic composition of a target according to the invention.

An advantage of the invention is that the drawbacks of the known embodiments are overcome by blocking layers made of materials of the following characteristics:

(a) the width of their banned energy band is greater than the width of the banned energy band in the photoconductive layer;

(b) are appropriately alloyed with impurities so that both types of charge cannot accumulate at their interface with the photoconductive layer.

the following conditions are observed (see Fig. 4):

(a) ZE ^bd > Δ E ^f and Δ E ^be > Δ E ^f ,.

E and Δ E, the widths of forbidden bands of energy in the electron blocking layer _{of p} f _p f _> _ PBE BE _F ^E F ^E V "F ^E V ^{E E} C - ^E F - ^E C ^d - ^Ε" 'wherein

AE ^bd , and holes;

b) wherein the symbols E ^, E ^be and E ^bd denote Fermi energy in the photoconductive layer and in the electron-blocking and hole-blocking layers, respectively; furthermore, E ^ and E ^bd are the bottom energy of the conductive bands in the phototape t β conductive layer and the hole blocking layer, and the symbols By and E _y are the peak energy of the valence band in the photoconductive and electron blocking layer. Such a target structure (see.

5) can be realized, for example, on a glass substrate 1 provided with a transmissive, electrically conductive signal electrode made of tin or indium oxide, or both 2 with a layer of alloyed α-SiN 3 which is n-type and is proto-blocking for holes.

- λ y—

Elements of the fifth or sixth group of the periodic system, such as phosphorus, may be used as alloying impurities. Another deposited layer 40 is an intrinsic α-Si: H layer which has a high photoelectric conductivity. Finally, an electron blocking layer 5 is formed, which is formed from the α-SiN β-type, using elements of the second or third group of the periodic system, such as boron, as admixtures.

The decomposition of suitable SiH 2 -based gas mixtures in the high-frequency discharge may be advantageously used to prepare the individual thin films.

The proposed solution of the blocking layers by means of alloyed materials solves another problem concerning the inertia of the vidicon tubes. By appropriate alloying and appropriate voltage selection at the target, the magnitude of the dark current can be increased to a level that would otherwise have been achieved by illuminating the target so that the inertia caused by the electron beam sensing mechanism drops below 5% after 60 ms.

245592 4

Claims (1)

SUBJECT OF THE INVENTION Target vidicon pickup tubes or other electro-optical transducers based on amorphous semiconductors, in particular amorphous silicon, characterized in that the blocking layers for holes and electrons are formed of semiconducting materials alloyed with elements of the second and third, fifth and sixth groups of the periodic system and have the energy band by at least 0.001 eV greater than the width of the banned band of the photoconductive layer.