CN112349564A

CN112349564A - Transmission-type NEA GaAs photocathode with graphene gate layer

Info

Publication number: CN112349564A
Application number: CN202011103548.0A
Authority: CN
Inventors: 富容国; 段赐琛
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2020-10-15
Filing date: 2020-10-15
Publication date: 2021-02-09

Abstract

The invention discloses a transmission type NEA GaAs photocathode with a graphene gate layer, which comprises a transmission type NEA GaAs photocathode inner core and a vacuum cavity shell. Wherein the inner core structure of the transmission type NEA GaAs photocathode comprises Si which are sequentially arranged from top to bottom₃N₄The device comprises an anti-reflection layer, a GaAlAs buffer layer, a GaAs emission layer, a Cs-O active layer and a high-quality graphene gate layer; the vacuum chamber is made of Corning 7056^#Glass, indium sealing filler, kovar metal and ceramic cavity. According to the invention, the suspended graphene gate layer with good electrical property is added on the basis of the traditional NEA photocathode structure, so that the service life of the cathode is prolonged and the structural stability of the cathode is enhanced under the condition that the photocathode maintains higher quantum efficiency.

Description

Transmission-type NEA GaAs photocathode with graphene gate layer

Technical Field

The invention belongs to the technical field of semiconductors, and particularly relates to a transmission type NEA GaAs photocathode with a graphene gate layer.

Background

The appearance of NEA GaAs photocathodes is a qualitative leap in the development history of photocathodes, and the NEA GaAs photocathodes play an important role in the fields of low-light-level imaging, vacuum electron sources, solar energy conversion and the like.

The main structure of the activated transmission type NEA GaAs photocathode commonly used at present is divided into 5 layers, namely a glass layer and a Si layer from top to bottom₃N₄Antireflection layer, Ga_1-xAl_xThe organic light-emitting diode comprises an As window layer, a GaAs emission layer and Cs-O active layers which are alternately covered. Currently, NEA GaAs cesium activation in light source applicationsThe service life of the photocathode is less than 500 h; tests in an ultrahigh vacuum system show that under the illumination condition of 300nm, the cesium-activated GaN photocathode rapidly reduces the quantum efficiency after continuously operating for about 10 hours, and the photocurrent is reduced by more than 85% within 20 hours of continuous operation. Regarding the lifetime problem of NEA GaAs photocathodes, one of the major contributing factors is atomic desorption of the active layer, resulting in the destruction of the NEA structural state at the cathode surface.

When the NEA GaAs photocathode works, along with continuous emission of electrons, cesium atoms and oxygen atoms of the activation layer are continuously separated from the emission layer due to the impact of the electrons, so that the surface potential barrier is slowly increased, and the integral quantum efficiency of the photocathode is influenced to be continuously reduced. In addition, even when the photocathode is not in an operating state, the adsorbed atoms of the active layer are continuously released due to vibration of the external environment or the like in a natural storage state. Overall, therefore, older NEA photocathodes tend to have a short lifetime and a rapid degradation over prolonged periods of sustained operation.

Disclosure of Invention

The present invention is directed to solve the above problems of the prior art, and an object of the present invention is to provide a transmissive NEA GaAs photocathode having a graphene gate layer.

The technical solution for realizing the purpose of the invention is as follows: a transmission-type NEA GaAs photocathode with a graphene gate layer comprises Corning 7056 arranged from top to bottom to form a closed vacuum cavity^#Glass, tubular ceramic chamber and anode part, wherein Corning 7056^#Annular kovar metal is arranged between the contact surfaces of the glass and the tubular ceramic cavity; a transmission-type photocathode inner core is arranged in the tubular ceramic cavity, and the inner core comprises a Si3N4 antireflection layer, a GaAlAs buffer layer, a GaAs emission layer, a Cs-O active layer and a suspended graphene gate layer which are sequentially arranged from top to bottom in an overlapped mode; corning 7056^#Indium sealing filler is filled between the glass and the kovar metal to connect the photocathode inner core and the kovar metal; the anode part is connected with kovar metal through a tubular ceramic cavity, and a vacuum channel is formed between the lower end of the tubular ceramic cavity and the inner core of the photocathode; corning 7056^#The lower surface of the glass was bonded to a Si3N4 antireflective layer.

Further, the photocathode inner core is cylindrical.

Furthermore, the graphene gate layer is fixedly suspended through an Au/Cu graphene bracket arranged on the inner wall of the tubular ceramic cavity.

Compared with the prior art, the invention has the following remarkable advantages: 1) the graphene gate layer with good electrical property is added on the surface of the Cs-O active layer, so that the structural stability of the Cs-O atomic layer of the transmission GaAs photoelectric cathode is maintained under the condition that the quantum efficiency is not reduced, the service life of the cathode is prolonged, and the stability of the cathode is enhanced; 2) the adopted graphene is in a film shape, the surface potential barrier can be ignored, electrons can easily overflow to vacuum, and the quantum efficiency as high as possible is obtained; 3) the adopted graphene is a zero band gap material, and due to the adoption of a suspension structure, the graphene material is not in direct contact with the substrate, the interaction between the graphene material and the substrate is extremely weak, the electrical property of the graphene film is close to the intrinsic state of the graphene film, and the electron mobility is high.

The present invention is described in further detail below with reference to the attached drawing figures.

Drawings

FIG. 1 is a schematic diagram of a transmissive NEA GaAs photocathode with a graphene gate layer in one embodiment.

Figure 2 is a diagram of the overall operation of a transmissive NEA GaAs photocathode with a graphene gate layer in one embodiment.

Fig. 3 is a diagram of the operation mechanism of a graphene gate layer in a transmissive NEA GaAs photocathode with a graphene gate layer in one embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In one embodiment, in conjunction with fig. 1, there is provided a transmissive NEA GaAs photocathode with a graphene gate layer, the photocathode comprising a closed-form closed structureCorning 7056 for a vacuum chamber arranged from top to bottom^#Glass 7, tubular ceramic chamber 10 and anode part 11, Corning 7056^#An annular kovar metal 9 is arranged between the contact surfaces of the glass 7 and the tubular ceramic cavity 10; a transmission-type photocathode inner core is arranged in the tubular ceramic cavity 10, and the inner core comprises a Si3N4 antireflection layer 1, a GaAlAs buffer layer 2, a GaAs emission layer 3, a Cs-O active layer 4 and a suspended graphene gate layer 5 which are sequentially arranged from top to bottom in an overlapped mode; corning 7056^# Indium sealing filler 8 is filled between the glass 7 and the kovar metal 9 to connect the photocathode inner core and the kovar metal 9; the anode part 11 is connected with kovar metal 9 through a tubular ceramic cavity 10, and a vacuum channel is formed between the lower end of the tubular ceramic cavity 10 and the inner core of the photocathode; corning 7056^#The lower surface of glass 7 was bonded to Si3N4 antireflective layer 1 to act as a top window.

Further, in one embodiment, the photocathode core is cylindrical and has a diameter of about 15mm to 20 mm.

Further, in one embodiment, the graphene gate layer 5 is fixed and suspended by an Au/Cu graphene bracket 6 disposed on the inner wall of the tubular ceramic cavity 10.

Further, in one of the embodiments, the Si is₃N₄The thickness of the anti-reflection layer 1 is 100 nm-200 nm.

Further, in one embodiment, the GaAlAs buffer layer 2 is p-type with a doping concentration of 1.0 × 10¹⁸cm^-3～1.0×10¹⁹cm^-3The total thickness is 500 nm-1000 nm.

Further, in one embodiment, the GaAs emission layer 3 is p-type with a doping concentration of 1.0 × 10¹⁸cm^-3～1.0×10¹⁹cm^-3The total thickness is 1000 nm-3000 nm.

Further, in one embodiment, the Cs-O active layer 4 is formed by applying a vacuum 10 to the Cs-O active layer^-8And the GaAs emitting layer is adsorbed on the lower surface of the GaAs emitting layer 3 in an environment above Pa by adopting a Cs and O alternate activation mode.

Further, in one embodiment, the Cs — O active layer 4 has a thickness of 0.5nm to 1.5 nm.

Further, in one embodiment, the graphene gate layer 5 has a larger diameter than the GaAs emission layer 3, and is a multilayer graphene film prepared by a chemical vapor deposition method and subjected to clean transfer.

Further, in one embodiment, the total thickness of the graphene thin film is 2nm to 10nm, and the total thickness of the graphene gate layer is 200nm to 600 nm.

With reference to fig. 2, the working mechanism of the present invention is: incident photons are transmitted through Corning 7056^# Glass 7 and Si₃N₄The anti-reflection layer 1 reaches the upper surface of the substrate of the transmission type photoelectric cathode inner core, electrons in the cathode enter a conduction band through the excitation of incident photons to become photoelectrons, and the photoelectrons are accelerated and transported through the buffer layer GaAlAs2 and the GaAs emission layer 3, escape to an inner cavity vacuum region through the surface barrier overcome by the lower surface of the Cs-O activation layer 4, and pass through the high-quality graphene gate layer 5 to reach the anode part 11.

With reference to fig. 3, the suspended graphene gate layer with good electrical properties is added on the surface of the Cs-O active layer, so that atoms in the Cs-O atomic layer are prevented from falling off, and the structural stability of the Cs-O atomic layer is maintained. In addition, as shown in fig. 3, the thin film graphene with zero band gap is adopted in the invention, the surface barrier is negligible, and electrons easily overflow to vacuum, so that the quantum efficiency as high as possible is obtained. In general, the graphene gate layer plays a role in screening atoms which cannot pass through and electrons which can pass through, and has important significance in improving the service life of the NEA photocathode.

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. AThe utility model provides a transmission-type NEA GaAs photocathode with graphite alkene grid layer, its characterized in that, photocathode includes the Corning 7056 that sets up from top to bottom that constitutes airtight vacuum cavity^#A glass (7), a tubular ceramic chamber (10) and an anode part (11), wherein Corning 7056^#An annular kovar metal (9) is arranged between the contact surfaces of the glass (7) and the tubular ceramic cavity (10); a transmission-type photocathode inner core is arranged in the tubular ceramic cavity (10), and the inner core comprises a Si3N4 antireflection layer (1), a GaAlAs buffer layer (2), a GaAs emission layer (3), a Cs-O activation layer (4) and a suspended graphene gate layer (5) which are sequentially arranged from top to bottom in a superposed manner; corning 7056^#Indium sealing filler (8) is filled between the glass (7) and the kovar metal (9) to connect the photocathode inner core and the kovar metal (9); the anode part (11) is connected with kovar metal (9) through a tubular ceramic cavity (10), and a vacuum channel is formed between the lower end of the tubular ceramic cavity (10) and the inner core of the photocathode; corning 7056^#The lower surface of the glass (7) is bonded to the Si3N4 antireflection layer (1).

2. The transmissive NEA GaAs photocathode of claim 1, wherein the photocathode core is cylindrical.

3. The transmissive NEA GaAs photocathode of claim 1 or 2, wherein the graphene gate layer (5) is fixedly suspended by Au/Cu graphene supports (6) disposed on the inner wall of the tubular ceramic cavity (10).

4. The transmissive NEA GaAs photocathode of claim 3 having a graphene gate layer, wherein said Si is₃N₄The thickness of the anti-reflection layer (1) is 100 nm-200 nm.

5. The transmissive NEA GaAs photocathode of claim 4, wherein the GaAlAs buffer layer (2) is p-type with a doping concentration of 1.0 x 10¹⁸cm^-3～1.0×10¹⁹cm^-3The total thickness is 500 nm-1000nm。

6. The transmissive NEA GaAs photocathode of claim 5, wherein the GaAs emission layer (3) is p-type with a doping concentration of 1.0 x 10¹⁸cm^-3～1.0×10¹⁹cm^-3The total thickness is 1000 nm-3000 nm.

7. The transmissive NEA GaAs photocathode with a graphene gate layer according to claim 6, wherein the Cs-O active layer (4) is formed by applying a vacuum of 10 degrees^-8And the GaAs emitting layer is adsorbed on the lower surface of the GaAs emitting layer (3) in an environment above Pa by adopting a Cs and O alternate activation mode.

8. The transmissive NEA GaAs photocathode with a graphene gate layer according to claim 7, wherein the Cs-O active layer (4) has a thickness of 0.5nm to 1.5 nm.

9. The transmissive NEA GaAs photocathode of claim 8, wherein the graphene gate layer (5) is larger in diameter than the GaAs emission layer (3) and is a multi-layer graphene thin film prepared by chemical vapor deposition and subjected to clean transfer.

10. The transmissive NEA GaAs photocathode of claim 9, wherein the graphene thin film has a total thickness of 2nm to 10nm, and the graphene gate layer has a total thickness of 200nm to 600 nm.