阅读说明：本技术 一种提高砷化镓光电阴极发射性能的激活方法 (Activation method for improving gallium arsenide photocathode emission performance ) 是由 冯琤 刘健 张益军 钱芸生 宋宇飞 赵静 于 2020-07-20 设计创作，主要内容包括：本发明公开了一种提高砷化镓光电阴极发射性能的激活方法,包括步骤1在超高真空系统中对具有原子级清洁表面的GaAs光电阴极进行高温加热；2超高真空系统温度降至室温后开启铯源量子效率逐渐增长直至到达首个铯峰；保持铯源开启当量子效率保持稳定或下降至首个铯峰的80%~85%时,打开氟源,同时铯源保持开启,量子效率再次开始上升,直到达到第二个峰值；关闭氟源,量子效率开始下降,当量子效率到达谷底时,关闭铯源,量子效率会转而上升到第3个峰值,然后保持比较好的稳定性；3再次将GaAs光电阴极放入超高真空系统中进行加热处理,并重复步骤2后,结束激活过程。本发明可以得到量子效率高、稳定性更好的GaAs光电阴极。(The invention discloses an activation method for improving the emission performance of a gallium arsenide photocathode, which comprises the following steps of 1, heating a GaAs photocathode with an atomic-scale clean surface at a high temperature in an ultrahigh vacuum system; 2, after the temperature of the ultrahigh vacuum system is reduced to room temperature, the quantum efficiency of the cesium source is started to gradually increase until the first cesium peak is reached; keeping the cesium source on, when the quantum efficiency keeps stable or drops to 80% -85% of the first cesium peak, opening the fluorine source, keeping the cesium source on, and starting the quantum efficiency to rise again until reaching a second peak value; when the fluorine source is turned off, the quantum efficiency begins to decrease, when the quantum efficiency reaches the valley bottom, the cesium source is turned off, the quantum efficiency can rise to the 3 rd peak value, and then the good stability is kept; and 3, putting the GaAs photocathode into the ultrahigh vacuum system again for heating treatment, and finishing the activation process after repeating the step 2. The invention can obtain the GaAs photocathode with high quantum efficiency and better stability.)

1. An activation method for improving the emission performance of a gallium arsenide photocathode is characterized in that: the method specifically comprises the following steps:

step 1, performing first high-temperature heating on a GaAs photoelectric cathode with an atomic-scale clean surface in an ultrahigh vacuum system;

step 2, after the temperature of the ultrahigh vacuum system is reduced to room temperature, the cesium source is started, and the quantum efficiency of the GaAs photocathode is gradually increased until the first cesium peak is reached; keeping the cesium source on, and turning on a fluorine source when the equivalent quantum efficiency is kept stable or is reduced to 80-85% of a first cesium peak, and simultaneously keeping the cesium source on, so that the quantum efficiency begins to rise again; until reaching the second peak value, namely detecting that the quantum efficiency is reduced, closing the fluorine source, starting to reduce the quantum efficiency, and closing the cesium source when the quantum efficiency reaches the valley bottom, namely the quantum efficiency is not reduced any more; the quantum efficiency of the GaAs photocathode can rise to the 3 rd peak value in turn, and then relatively good stability is kept;

And 3, performing high-temperature heating treatment on the ultrahigh vacuum system placed in the GaAs photoelectric cathode for the second time, and finishing the activation process after repeating the step 2.

2. The activation method for improving the emission performance of a gallium arsenide photocathode according to claim 1, wherein the first high temperature heating in step 1 is performed at 640-660 ℃ for 15-20 minutes.

3. The activation method for improving the emission performance of GaAs photocathode according to claim 1, wherein step 2 is performed under 632nm or 670nm laser illumination.

4. The activating method for improving the emission performance of a gallium arsenide photocathode according to claim 1, wherein the second high temperature heating in step 3 is performed at 550-610 ℃ for 15-20 minutes.

5. The activation method for improving the emission performance of GaAs photocathode according to claim 1, wherein the vacuum degree of said ultra-high vacuum system is not lower than 1 x 10 a 7 Pa.

6. The activation method for improving the emission performance of GaAs photocathode according to claim 1, wherein the oxide layer on the surface of the GaAs photocathode is atomically clean and has a thickness not exceeding 3 angstroms.

Technical Field

The invention belongs to the technical field of semiconductor photoelectric emission material preparation, and particularly relates to an activation method for improving the emission performance of a gallium arsenide photoelectric cathode.

Background

The GaAs photocathode has the advantages of high quantum efficiency, spectral response range, good imaging effect, high response speed and the like, so the GaAs photocathode has wide application prospect in the fields of low-light night vision imaging devices, spin-polarized electron sources, semiconductor sensitive devices and the like. In the research process of photocathodes, people are constantly dedicated to research methods and technologies for improving quantum efficiency and stability. For example, a graded band gap or DBR structure is adopted to improve the light absorption capacity and the electron transport capacity in the photocathode, so that the emission efficiency of the photocathode is improved; and for example, solid oxygen source activation is adopted to replace gaseous oxygen source activation, so that the oxygen flow in the activation process can be controlled more accurately, and the emission efficiency and stability of the photocathode are improved.

The preparation of the GaAs photocathode with high quantum efficiency and good stability is always a research hotspot of the application of the photocathode at present. However, the decay of the cathode quantum efficiency with time is still a technical problem in the practical process. The prior art application number is: 2016101685912 the invention name is: an activation method for improving the stability of a gallium arsenide photocathode is disclosed, which is a commonly used activation method in China at present, wherein a GaAs photocathode with negative electron affinity is prepared in a mode that cesium and oxygen are alternately covered on the surface of a clean GaAs material in an ultrahigh vacuum environment, the activation of the cesium and the oxygen enables the surface vacuum level of the GaAs photocathode to be lower, electrons reaching the surface of the cathode are easier to escape to vacuum, and the quantum efficiency of the cathode is greatly improved. There are problems in that: in the activation process, the current ratio of different cesium sources and oxygen sources and the starting steps of different cesium sources and oxygen sources can affect the activation effect of the GaAs photocathode, and the current experiments show that the GaAs photocathode obtained by the activation mode of alternately covering cesium and oxygen has unsatisfactory emission performance, especially poor stability.

Disclosure of Invention

1. The technical problem to be solved is as follows:

aiming at the technical problems, the invention provides an activation method for improving the emission performance of a gallium arsenide photocathode, and solves the problem that the emission performance, namely the emission efficiency and the stability of the prepared GaAs photocathode are not good enough in the prior art.

2. The technical scheme is as follows:

an activation method for improving the emission performance of a gallium arsenide photocathode is characterized in that: the method specifically comprises the following steps:

step 1, performing first high-temperature heating on a GaAs photoelectric cathode with an atomic-scale clean surface in an ultrahigh vacuum system.

Step 2, after the temperature of the ultrahigh vacuum system is reduced to room temperature, the cesium source is started, and the quantum efficiency of the GaAs photocathode is gradually increased until the first cesium peak is reached; keeping the cesium source on, and turning on a fluorine source when the equivalent quantum efficiency is kept stable or is reduced to 80-85% of a first cesium peak, and simultaneously keeping the cesium source on, so that the quantum efficiency begins to rise again; until reaching the second peak value, namely detecting that the quantum efficiency is reduced, closing the fluorine source, starting to reduce the quantum efficiency, and closing the cesium source when the quantum efficiency reaches the valley bottom, namely the quantum efficiency is not reduced any more; the quantum efficiency of the GaAs photocathode can turn up to the 3 rd peak and then maintain relatively good stability.

And 3, performing high-temperature heating treatment on the ultrahigh vacuum system placed in the GaAs photoelectric cathode for the second time, and finishing the activation process after repeating the step 2.

Further, the first high-temperature heating in the step 1 is carried out, wherein the heating temperature is 640-660 ℃, and the heating time is 15-20 minutes.

Further, step 2 is carried out under laser irradiation at 632nm or 670 nm.

Further, the second high-temperature heating in the step 3 is carried out, wherein the heating temperature is 550-610 ℃, and the heating time is 15-20 minutes.

Further, the vacuum degree of the ultrahigh vacuum system is not lower than 1 x 10^7 Pa.

Further, the oxide layer thickness on the surface of the GaAs photocathode which is atomically clean does not exceed 3 angstroms.

3. Has the advantages that:

(1) the GaAs photocathode adopting cesium source activation and fluorine activation has better emission performance.

(2) The GaAs photocathode prepared by the method has high quantum efficiency and longer working life and storage life.

(3) The operation steps of the invention are less, the cesium source is always kept in the open state, and the open and close of the fluorine source only need to judge whether the quantum efficiency reaches the valley value and the peak value, thus providing a better activation method for the automatic control activation of the computer.

Drawings

FIG. 1 is an activation flow diagram of the present invention;

FIG. 2 is a graph showing the change in quantum efficiency during activation of cesium fluoride in an embodiment of the present invention;

FIG. 3 is a graph comparing cesium fluorine activated and cesium oxygen activated quantum efficiencies in an embodiment of the present invention;

FIG. 4 is a graph comparing the stability of cesium fluorine activation and cesium oxygen activation in accordance with examples of the present invention.

Detailed Description

An activation method for improving the emission performance of a gallium arsenide photocathode is characterized in that: the method specifically comprises the following steps:

step 1, performing first high-temperature heating on a GaAs photoelectric cathode with an atomic-scale clean surface in an ultrahigh vacuum system.

Step 2, after the temperature of the ultrahigh vacuum system is reduced to room temperature, the cesium source is started, and the quantum efficiency of the GaAs photocathode is gradually increased until the first cesium peak is reached; keeping the cesium source on, and turning on a fluorine source when the equivalent quantum efficiency is kept stable or is reduced to 80-85% of a first cesium peak, and simultaneously keeping the cesium source on, so that the quantum efficiency begins to rise again; until reaching the second peak value, namely detecting that the quantum efficiency is reduced, closing the fluorine source, starting to reduce the quantum efficiency, and closing the cesium source when the quantum efficiency reaches the valley bottom, namely the quantum efficiency is not reduced any more; the quantum efficiency of the GaAs photocathode can turn up to the 3 rd peak and then maintain relatively good stability.

And 3, performing high-temperature heating treatment on the ultrahigh vacuum system placed in the GaAs photoelectric cathode for the second time, and finishing the activation process after repeating the step 2.

Further, the first high-temperature heating in the step 1 is carried out, wherein the heating temperature is 640-660 ℃, and the heating time is 15-20 minutes.

Further, step 2 is carried out under laser irradiation at 632nm or 670 nm.

Further, the second high-temperature heating in the step 3 is carried out, wherein the heating temperature is 550-610 ℃, and the heating time is 15-20 minutes.

Further, the vacuum degree of the ultrahigh vacuum system is not lower than 1 x 10^7 Pa.

Further, the oxide layer thickness on the surface of the GaAs photocathode which is atomically clean does not exceed 3 angstroms.