JPH03261029A - High sensitive electron emitter and light receiving device - Google Patents

Abstract

PURPOSE:To hold the emission of thermoelectrons after the irradiation of light is stopped and count it to increase the amount of output charge (sensitiveness) relative to the number of incoming photons by radiating light to a preset half- insulating semiconductor in an electric field of a preset value or more. CONSTITUTION:A half-insulating semiconductor 1-1 mainly composed of GaAs has both sides provided with a mesh-shaped film electrode 1-2 and a Schottky- type electrode 1-3, respectively, across which voltage is applied to cause not less than 1KV/cm electric field in the semiconductor 1-1. Long wave-length light is radiated from an energy gap in the semiconductor 1-1, so that the Fermi level of the semiconductor moves to a conduction band and the emission of thermoelectrons are increased and still remains in a greatly increased state after the irradiation of light is stopped. In this way, electron current which is taken out of the semiconductor into a vacuum is counted at the timing of light irradiation to know its sensitiveness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a highly sensitive photoelectron emitter and a photodetector.

[Conventional technology]

Although the photoelectron emission phenomenon has been applied to various devices,
The quantum efficiency with respect to optical energy is low and the amount of signal is small.

In particular, in the wavelength region longer than 900 nm, Ag
Only the -〇-Cs (so-called Sl) photoelectron emitter is in practical use, and the sensitivity of this photoelectron emitter is also extremely low. To this end, various studies are being conducted, and if the photoelectron emitter has the ability to multiply photoelectrons, it will lead to an increase in sensitivity.

Although photoelectron emitters having a multiplication function have not been put to practical use in the prior art, some photoelectron emitters have been devised in hopes of lowering the surface barrier by utilizing the electric field effect. This technique is based on a well-known phenomenon in which electron multiplication occurs due to avalanche amplification caused by a strong electric field near the surface, and the multiplied electrons are emitted.

Furthermore, in the CsSb type photoelectron emitter, which has been most commonly used in the past, there is a so-called fatigue effect in which the amount of thermionic radiation increases significantly after being irradiated with strong light, which is well known.

[Problem to be solved by the invention]

However, in the conventional technique of multiplying photoelectrons using avalanche amplification, the multiplication factor of avalanche amplification is only about 100 times at most, so that sufficient sensitivity of the photoelectron emitter could not be obtained. Further, the electric field strength applied to the photoelectron emitter cannot be expected to be multiplied much because the physical property constants of the element are not designed solely for avalanche multiplication. Furthermore, in avalanche multiplication, the signal-to-noise ratio always deteriorates because the multiplication factors of the signal and the noise are different.

Furthermore, the increase in the amount of thermionic radiation due to the fatigue effect in the conventional C5-8b type photoelectron emitter is a temporary phenomenon that occurs only when extremely strong light is irradiated, and the extent of this increase is also small. .

[Means to solve the problem]

The present invention has been made to solve these problems, and includes a light irradiation means for irradiating light, an electric field application means for applying an electric field of 1 KV/beat or more, and a light irradiation means for applying the electric field. It is composed of a semi-insulating semiconductor that has an amplification function that, when irradiated with light, thermionic emission from the element increases significantly compared to the value before irradiation with light.

[Effect]

Due to the high electric field applied to the semi-insulating semiconductor, the Fermi level energy position of the semiconductor increases, and the thermal electrons emitted in vacuum after light irradiation are sufficiently multiplied. Furthermore, the current due to this multiplication phenomenon flows continuously.

[Example] Next, an example of an extremely sensitive photoelectron emitter according to the present invention will be described.

Thermionic emission of semiconductors is a phenomenon in which electrons thermally excited from the Fermi level to the conduction band are emitted into vacuum, limited by the escape probability determined by the height of the surface barrier. Therefore, in a situation where the surface barrier does not change much, increasing the number of electrons flowing into the conduction band increases the amount of thermionic radiation.

In addition, the normal photoelectron emission phenomenon is a phenomenon in which photon energy excites electrons from the valence band to the conduction band, increasing the amount of current flowing in the conduction band and increasing the number of electrons emitted into the vacuum. . The feature of the present invention is that it combines both of these phenomena. By moving the Fermi level position closer to the conduction band by light irradiation, thermal electron excitation is increased, and the amount of electrons emitted into the vacuum is increased. There are many things.

Since the amount of electrons extracted is controlled by the optical input, it is completely different from conventional photoelectron emission phenomena.

This phenomenon has not been previously reported and requires a new interpretation. The currently assumed interpretation will be explained in more detail using examples of the present invention. FIG. 1 shows an example in which the photoelectron emitter of the present invention is formed using semi-insulating GaAs.

In Fig. 1, the reference numeral 1-1 is a semi-insulating GaAs semiconductor, and the reference numeral 1-2 is a mesh-like thin film electrode or an island-like thin film electrode made to allow light to enter and not interfere with electron emission. . In addition, numerals 1-3 are Schottky electrodes;
For example, it is W-Si, etc., and is an electrode for collecting electrons. Further, the electrode 1-2 is surface-treated with an alkali metal such as Cs or an alkali oxide so as to lower the surface barrier and facilitate electron emission. Electrode 1-2.1-3
A voltage is applied between them with the polarity shown in the figure, and the electric field generated within the semiconductor 1-1 is 1 KV/am or more.

A GaAs semiconductor 1 is attached to the photoelectron emitter constructed in this way.
Light with a long wavelength is irradiated from an energy gap of -1. The irradiated light passes through the GaAs semiconductor 1-1 and thus reaches the electrode 1-3.

In the electrode 1-3, the light excites electrons, crosses the Schottky barrier existing between the electrode 1-3 and the GaAs semiconductor 1-1 by internal emission, and injects electrons into the GaAs semiconductor 1-1. These electrons are captured in a deep level existing in the GaAs semiconductor 1-1 while traveling to the electrode 1-2.

Before an electron is captured, that is, before it is irradiated with light, '
The Fermi level in the GaAs semiconductor 1-1 is
Located in the middle of the energy gap. Therefore, the number of electrons thermally excited to the conduction band is smaller than the Fermi level,
As a result, the number of thermoelectrons extracted into the vacuum is also small. However, in a situation where electron capture occurs due to light irradiation, the Fermi level moves close to the conduction band, so
The number of electrons thermally excited in the conduction band is large, and the amount of thermionic radiation is also large.

By the way, the situation in which the Fermi level exists near the conduction band continues because the GaAs semiconductor 1-1 has changed into a completely different substance, an n-type semiconductor. In other words, even if the light is cut off, thermionic emission remains significantly increased.

As a result, in the thermionic irradiation, the amount of externally emitted electrons is significantly increased compared to before the light irradiation.

Since the amount of emitted electrons is controlled by light in this way, it can be said that an extremely sensitive photoelectron emitter is formed.

Currently, this new phenomenon is interpreted as described above, but it is not confirmed.

By the way, this situation of increased thermionic radiation is caused by the semiconductor 1
This continues until the electric field applied to -1 is cut off and electron injection is cut off. Therefore, it cannot be used as a photoelectron emitter for general-purpose photodetection, but it can be used as a detector in situations where the timing of optical input is known in advance and a reset function can be added, or this element can be made into another element so that it does not operate. It can be applied to image pickup tubes for infrared images.

Furthermore, since thermionic emission continues, by integrating it, the amount of output charge relative to the number of incident photons, that is, the sensitivity, can be increased as much as possible by extending the integration time. This amplification effect also significantly improves the S/N ratio. For these applications, the temperature of the semiconductor can be adjusted to select the optimum state. In general, keeping it at a low temperature will give better results.

By the way, in the embodiment shown in FIG.
When light of a single wavelength is incident from the energy gap of .

For use on the single wavelength side, the electrode 1-3 may be made a transparent electrode and light may be incident from the electrode 1-3 side. In this case, a photoelectron due to excitation from the valence band becomes the first trapped electron.

In the description of the above embodiments, the method of generating photoelectrons that are initially trapped, the surface treatment that lowers the surface barrier for electron emission, etc. are not the essence of this patent, but are merely applications. The essence of this patent is that the discovery that light irradiation generates electron traps and increases the Fermi level, resulting in a significant increase in thermionic emission, and that this increase continues even after the light irradiation is cut off. It is applied to the body.

〔Effect of the invention〕

As explained above, according to the present invention, due to the high electric field applied to the semi-insulating semiconductor, the Fermi level energy position of the semiconductor increases, and thermionic electrons are sufficiently multiplied after light irradiation. Furthermore, the current due to this multiplication phenomenon flows continuously.

Therefore, although under limited conditions, it is possible to obtain a high amount of electron emission using the infrared light irradiation 11.

This can be applied to a variety of devices, even though good photoelectron emitting surfaces for infrared light have not yet been realized.

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[Brief explanation of drawings]

FIG. 1 is a block diagram of a photoelectron emitter according to an embodiment of the present invention. 1-1...GaAs semiconductor, 1-2...Mesh electrode or island electrode, 1-3...Schottky electrode.

Claims (1)

[Scope of Claims] 1. A light irradiation means that irradiates light, an electric field application means that applies an electric field of 1 KV/cm or more, and an element that is irradiated with light from the light irradiation means while applying this electric field. A high-sensitivity photoelectron emitter made of a semi-insulating semiconductor, characterized by having an amplification function that greatly increases thermionic emission from a semi-insulating semiconductor compared to the value before irradiation with light. 2. The highly sensitive photoelectron emitter according to claim 1, wherein the semi-insulating semiconductor is composed of a semiconductor mainly composed of GaAs. 3. The highly sensitive photoelectron emitter according to claim 1 or 2, wherein the surface of the semi-insulating semiconductor is treated with an alkali metal or an alkali oxide. 4. A light irradiation means for irradiating light, an electric field application means for applying an electric field of 1 KV/cm or more, and thermionic emission from the element is caused by irradiation of light from the light irradiation means while applying this electric field. a semi-insulating semiconductor having an amplification function that greatly increases the value before the light irradiation; a reset means for resetting the semi-insulating semiconductor at each clock timing using a photoelectron emitting surface of the semi-insulating semiconductor; A light-receiving device comprising: means for integrating the electron flow extracted from the semi-insulating semiconductor into a vacuum.