Semiconductor photoelectric cathode structure for improving quantum efficiency and low-light-level image intensifier

Abstract

The utility model discloses a semiconductor photoelectric cathode structure for improving quantum efficiency and a low-light-level image intensifier. The semiconductor photoelectric cathode structure comprises a photoelectric emission layer, an incidence window supporting layer and a substrate layer, the substrate layer is arranged between the photoelectric emission layer and the incident window supporting layer; the substrate layer is in contact with the photoelectric emission layer and the incident window supporting layer. And the substrate layer is an amorphous electret material layer and / or a ferroelectric electret material layer with negative fixed charges. According to the structure, the quantum efficiency of the photoelectric emission layer can be effectively improved, the back diffusion of photoelectrons in the photoelectric emission layer is inhibited, and the sensitivity and noise of the cathode can be effectively improved. As the photoelectrons moving towards the supporting layer are suppressed, thermal noise and thermal emission electrons generated by the photoelectric emission layer can be effectively reduced, and the noise of the photoelectric cathode can be effectively reduced.

Description

Technical Field

[0001] The present application relates to the field of photocathode technology, and in particular to a semiconductor photocathode structure for improving quantum efficiency and a low-light image intensifier. Background Art

[0002] Electromagnetic wave detectors such as image intensifiers and photomultiplier tubes detect targets by converting received electromagnetic and light wave signals into electrical signals for multiplication or amplification.

[0003] Vacuum image intensifiers and photomultiplier tubes usually contain a photocathode, which converts the received electromagnetic radiation or light waves into electron flow emission and amplifies them through an electron multiplier device, thereby being able to detect weak electromagnetic radiation and light signals.

[0004] like Figure 1 As shown, this type of photocathode is usually composed of a transparent support layer 10 and a photoelectric emission layer 20 connected to the substrate. The support layer 10 is highly transparent to the incident light, and the incident light passes through the support layer 10 to reach the photoelectric emission layer 20, and then the photons are absorbed by the photoelectric emission layer 20 and generate photoelectrons, a part of which moves along the direction of the incident light and is emitted from the emission surface of the photoelectric emission layer 20, and is then amplified by the photomultiplier device for detection and imaging.

[0005] The other part of the photoelectrons diffuse toward the support layer 10 in the opposite direction of the incident light due to collision and thermal motion, and then recombine with holes in the photoelectric emission layer 20 and are lost.

[0006] This part of the back-diffused photoelectrons is lost in the photoemission layer, which not only leads to a significant decrease in the cathode photoemission quantum efficiency, but also increases the dark current and thermal noise of the photocathode, which is not conducive to the improvement and enhancement of the device's detection performance. The quantum efficiency of the photocathode is the number of emitted photoelectrons / the number of incident photons. As the number of back-diffused photoelectrons in the photoemission layer increases, the quantum efficiency of the photocathode decreases, affecting the luminescence performance of the device.

[0007] In the prior art for the above-mentioned problems, for example, CN101211730B and CN101859672A of Hamamatsu Corporation of Japan disclose an alkaline photocathode having an anti-reflection film layer and a metal oxide crystal layer between the support layer and the photoelectric emission layer, which significantly improves the quantum efficiency of the alkaline photocathode. CN104781903B of Photonis Company of France discloses a method for improving the cathode quantum efficiency by using a surface micro-nano diffraction grating anti-reflection layer to improve the light absorption rate of a semi-transparent photocathode. However, the above method still has no inhibitory effect on the loss of back-diffused electrons in the photoelectric emission layer. The CN113994220A patent discloses a method for improving the quantum efficiency of the photocathode by suppressing back-diffused electrons using field-assisted emission. However, this method requires the production of an additional transparent electrode layer and a dielectric layer on the photocathode, and requires the application of an additional voltage to control the potential difference between the transparent electrode layer and the photoelectric emission layer. This method not only increases the complexity of the structure, but also increases the probability of electrical breakdown of the photocathode when used in image tubes and photomultiplier tubes.

[0008] The information disclosed in the background technology section is only intended to increase the understanding of the overall background of the utility model, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to ordinary technicians in the field. Utility Model Content

[0009] In view of the above technical problems, the present application provides a semiconductor photocathode structure and a low-light image intensifier for improving quantum efficiency. The structure can suppress the diffusion of back-direction photoelectrons and improve quantum efficiency.

[0010] The present application provides a semiconductor photocathode structure for improving quantum efficiency, comprising: a photoelectric emission layer, an incident window support layer, and a substrate layer; the substrate layer is arranged between the photoelectric emission layer and the incident window support layer; the substrate layer is arranged in contact with the photoelectric emission layer and the incident window support layer respectively.

[0011] Preferably, the substrate layer is an amorphous electret material layer and / or a ferroelectret material layer with negative fixed charge.

[0012] Preferably, the base layer is a thin layer containing negative electrode material.

[0013] Preferably, the base layer is a LiNbO3 material thin layer or a LiNbO3 single crystal material layer.

[0014] Preferably, the thickness of the base layer is between 1 nm and 500 nm.

[0015] Preferably, the refractive index of the substrate layer is between the refractive index of the support layer and the refractive index of the photoelectric emission layer.

[0016] Preferably, the photocathode emission layer is a compound layer containing alkali metal and antimony.

[0017] Preferably, the thickness of the photoelectric emission layer is between 10 nm and 500 nm.

[0018] Preferably, the incident window supporting layer is a high-boron glass layer.

[0019] Another aspect of the present application provides a low-light level image intensifier, including: the above-mentioned photocathode structure.

[0020] The beneficial effects of this application include:

[0021] 1) The semiconductor photocathode structure with improved quantum efficiency provided in the present application is achieved by placing a substrate layer between a supporting layer and a photoelectric emission layer. Due to the positioning structure, the polar charges in the substrate layer generate an inward bias electric field in the interface region between the substrate layer and the photoelectric emission layer and cause the energy band of the semiconductor photoelectric emission layer to bend, thereby inhibiting the diffusion of photoelectrons generated by the photoelectric emission layer toward the supporting layer.

[0022] 2) The semiconductor photocathode structure with improved quantum efficiency provided by the present application can effectively improve the quantum efficiency of the photoemission layer, inhibit the back diffusion of photoelectrons in the photoemission layer, and effectively improve the sensitivity and noise of the cathode. Since the photoelectrons moving toward the supporting layer are inhibited, the thermal noise and thermal emission electrons generated by the photoemission layer can be effectively reduced, and the noise of the photocathode can be effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the photocathode structure in the prior art;

[0024] Figure 2 A schematic diagram of the structure of at least one embodiment provided in the present application;

[0025] Figure 3 A schematic diagram of the energy bands of the photocathode in at least one embodiment provided in the present application;

[0026] Figure 4 This is a comparison chart of cathode quantum efficiency obtained in the control example and the embodiment provided in this application;

[0027] Legend:

[0028] Photoelectric emission layer 33 , incident window support layer 11 , and substrate layer 22 . DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

[0031] The technical means that are not described in detail in this application and are not used to solve the technical problems of this application are all set according to the common knowledge in the field, and can be implemented in a variety of common knowledge settings.

[0032] See also Figures 2 to 4 The semiconductor photocathode structure with improved quantum efficiency provided in the present application includes: a highly transparent incident window support layer 11, a substrate layer 22 arranged on the bottom surface of the incident window support layer 11, and a semiconductor photoelectric emission layer 33 containing alkali metal elements arranged on the substrate layer 22.

[0033] The base layer 22 is an amorphous electret material layer and / or a ferroelectric electret material layer with negative fixed charge, specifically SiO2, Al2O3, HfO2 electret material, or the ferroelectric electret material is KNbO3, LiNbO3, BaTiO3. The amorphous electret material layer and the ferroelectric electret material layer with negative fixed charge can be stacked.

[0034] In a specific embodiment, the base layer 22 is a thin layer containing a negative electrode material, which is a thin layer of SiO2, Al2O3, HfO2 or LiNbO3 material, and is in contact with the photoelectric emission layer 33. The base layer 22 is formed according to the existing method in the art. The LiNbO3 material used is a ferroelectric with spontaneous polarization characteristics.

[0035] In the photocathode structure, the above-mentioned base layer 22 is placed between the supporting layer 11 and the photoelectric emission layer 33. Due to this position structure, the polarity charges in the base layer 22 will generate an internal bias electric field in the interface region between the base layer 22 and the photoelectric emission layer 33 and cause the energy band of the semiconductor photoelectric emission layer to bend, thereby inhibiting the photoelectrons generated by the photoelectric emission layer 33 from diffusing toward the supporting layer. Therefore, the quantum efficiency of the photoelectric emission layer 33 can be effectively improved.

[0036] Since the photoelectrons moving toward the support layer 11 are suppressed, the thermal noise and thermal emission electrons generated by the photoemission layer 33 can be effectively reduced, and the noise of the photocathode can be effectively reduced.

[0037] In a specific embodiment, the refractive index of the base layer 22 is between the refractive index of the support layer 11 and the refractive index of the photoelectric emission layer 33 , and the base layer 22 can function as an anti-reflection layer to increase the number of photons incident on the photoelectric emission layer 33 .

[0038] In one embodiment, the thickness of the base layer 22 is between 1 nm and 500 nm.

[0039] In a specific embodiment, during the preparation process, if the electrode material contained in the substrate layer 22 is a ferroelectric material with spontaneous polarization performance such as KNbO3, LiNbO3, BaTiO3, etc., the operation of unifying the polarization direction is performed according to the conventional operation in the field. An external electric field is applied to the substrate layer 22 for polarization, so that the polarization direction of the substrate layer 22 has a specific orientation, and then a photoelectric emission layer 33 is arranged on the substrate layer. Therefore, a surface charge layer is formed at the contact surface between the substrate layer 22 and the photoelectric emission layer 33, and the surface charge density is proportional to the spontaneous polarization intensity of the ferroelectric material.

[0040] In a specific embodiment, the base layer 22 is a LiNbO3 single crystal material layer, which has a better photoelectron suppression effect because it has a higher spontaneous polarization intensity and a higher paraelectric-ferroelectric structure phase transition temperature.

[0041] The charge layer bends the energy band near the contact surface between the photoelectric emission layer 33 and the substrate layer 22 and inhibits the diffusion of photoelectrons in the direction opposite to the photoelectric emission surface, thereby effectively improving the quantum efficiency of the photocathode.

[0042] In a specific embodiment, the photocathode emission layer 33 is a compound layer containing alkali metals and antimony, and the compound containing alkali metals and antimony in the layer is any one of Na2KSb, K2CsSb, Na3Sb, K3Sb, Cs3Sb, and Na2KSb(Cs); the settings of each film layer in the present application are all according to the commonly used methods in the field and are not repeated here.

[0043] The thickness of the photoelectric emission layer 33 is adjusted by those skilled in the art according to the spectral range of the incident light wave. In a specific embodiment, the thickness of the photoelectric emission layer 33 is between 10 nm and 500 nm.

[0044] The electret material contained in the negative electrode substrate layer 22 is not limited to the above-mentioned amorphous SiO2, Al2O3, HfO2 materials and KNbO3, LiNbO3, BaTiO3 ferroelectric materials. Based on the principle of the present invention, the substrate layer 22 is an electret material ion-doped compound layer, which is formed by the electret material ion-doped compound. This inhibits the movement of photoelectrons in the direction opposite to the photoelectric emission surface, thereby achieving the effect of improving the quantum efficiency of the photocathode.

[0045] Another aspect of the present application provides a low-light-level image intensifier, comprising: the above-mentioned photocathode structure. The photocathode structure and other undetailed components and structures necessary for use in the low-light-level image intensifier are arranged according to conventional methods in the art and are not described here.

[0046] Another aspect of the present application provides a photomultiplier tube, comprising: the above-mentioned photocathode structure. The photocathode structure and other undetailed components and structures necessary for use on the photomultiplier tube are arranged according to conventional methods in the art and are not described here.

[0047] Another aspect of the present application provides an electron tube, comprising: the above-mentioned photocathode structure. The photocathode structure and other undetailed components and structures necessary for use in the electron tube are arranged according to conventional methods in the art and are not described here.

[0048] Example

[0049] A substrate layer 22 with negatively charged polarity material is introduced between the incident window support layer 11 and the photoelectric emission layer 33, so that the internal bias field generated at the interface between the substrate layer 22 and the photoelectric emission layer 33 drives the photoelectrons to migrate toward the emission surface.

[0050] The incident window support layer 11 is made of high-boron glass, the base layer 22 is made of a z-cut LiNbO3 single crystal layer, and the photoelectric emission layer 33 is Na2KSb(Cs).

[0051] First, a 10 μm thick polarized z-tangent LiNbO3 is bonded to the glass support layer 11, and ICP and IBE etching are used to thin the LiNbO3 substrate layer 11 to a thickness of 20 nm. The polarization direction of the LiNbO3 substrate layer 11 points to the evaporated multi-alkali photoelectric emission layer Na2KSb (Cs).

[0052] Figure 3 Schematic diagram of the energy band of the photocathode with LiNbO3 substrate. Since the polarized LiNbO3 crystal surface has a 0.7C / m 2The bound charge density will attract free electrons to shield the surface bound charges, so that a fixed negative charge area is generated at the interface of the LiNbO3 substrate layer 22 and the photocathode emission layer. The energy band bending drives the photoelectrons near the interface of the substrate layer 22 and the photocathode emission layer 33 to move to the emission surface, reducing the electron recombination rate and improving the photoelectric emission quantum efficiency.

[0053] Comparison Example

[0054] The photoemissive layer is evaporated onto the glass support layer 11 to form the multi-alkali photocathode.

[0055] The cathode quantum efficiency of the photocathode obtained in the embodiment and the comparative example is measured respectively. The measuring method is that the modulated monochromatic light generated by the grating monochromator controlled by the computer is introduced into the photocathode through the optical fiber, the cathode current under the irradiation of the monochromatic light is amplified by the test system, and the data is input into the microcomputer through A / D conversion. After the microcomputer processes the collected data, the spectral response curve of the cathode quantum efficiency can be obtained.

[0056] Figure 4 In the embodiment, the spectral response curve of the quantum efficiency of a multi-alkali cathode with a LiNbO3 substrate layer 22 is shown.

[0057] The photocathode using the structure provided by the present application has higher sensitivity and higher quantum efficiency.

[0058] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A semiconductor photocathode structure for improving quantum efficiency, characterized in that: include: A photoelectric emission layer (33), an incident window support layer (11), and a substrate layer (22); the substrate layer (22) is arranged between the photoelectric emission layer (33) and the incident window support layer (11); and the substrate layer (22) is arranged in contact with the photoelectric emission layer (33) and the incident window support layer (11), respectively.

2. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The base layer (22) is an amorphous electret material layer and / or a ferroelectric electret material layer with negative fixed charge.

3. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The base layer (22) is a thin layer containing negative electrode material.

4. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The base layer (22) is a LiNbO3 material thin layer or a LiNbO3 single crystal material layer.

5. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The thickness of the base layer (22) is between 1 nm and 500 nm.

6. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The refractive index of the substrate layer (22) is between the refractive index of the incident window support layer (11) and the refractive index of the photoelectric emission layer (33).

7. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The photocathode emission layer (33) is a compound layer containing alkali metal and antimony.

8. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The thickness of the photoelectric emission layer (33) is between 10 nm and 500 nm.

9. The semiconductor photocathode structure for improving quantum efficiency according to claim 1, characterized in that: The incident window support layer (11) is a high-boron glass layer.

10. A low-light-level image intensifier, comprising: The photocathode structure according to any one of claims 1 to 9.

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