阅读说明：本技术 一种提高GaAs光电阴极稳定性的激活方法 (Activation method for improving stability of GaAs photocathode ) 是由 张益军 宋淳 荣敏敏 李诗曼 张锴珉 舒昭鑫 李姗 詹晶晶 钱芸生 于 2021-02-03 设计创作，主要内容包括：本发明公开了一种提高GaAs光电阴极稳定性的激活方法,包括两次Cs/Li/NF-3激活,分别在两次高温净化之后各进行一次激活。本发明的操作步骤少,Cs源一直保持开启状态,Li源的开启和关闭只需判定光电流的大小,NF-3的开启和关闭只需控制阀门开关,可操作性强,且光电阴极稳定性提升显著。(The invention discloses an activation method for improving the stability of a GaAs photocathode, which comprises two times of Cs/Li/NF 3 And (4) activating, wherein activation is carried out once after two times of high-temperature purification respectively. The method has less operation steps, the Cs source is always kept in an open state, and the opening and closing of the Li source only need to judge the magnitude of photocurrent, NF 3 The opening and closing of the photoelectric cathode can be realized by only controlling the valve switch, the operability is high, and the stability of the photoelectric cathode is obviously improved.)

1. An activation method for improving the stability of a GaAs photocathode is characterized by comprising the following specific steps:

step 1, chemically cleaning a GaAs photoelectric cathode, and putting the GaAs photoelectric cathode into an ultrahigh vacuum system for high-temperature purification;

step 2, turning on a Cs source and a Li source, starting the photocurrent to rise, turning off the Li source when the photocurrent reaches a first peak value, turning the photocurrent to fall, and turning on the NF of the ultra-high vacuum system when the photocurrent falls to 40% -60% of the first peak value current₃The photocurrent rises again through the air inlet valve;

step 3, turning on the Li source when the photocurrent rises to about 3 times of the first peak current, and turning off the Li source when the photocurrent drops to 60-80% of the previous peak current; when the photocurrent rises to about 6 times of the first peak current, the Li source is turned on, and when the photocurrent drops to 60-80% of the previous peak current, the Li source is turned off;

step 4, turning off NF when the photocurrent reaches the peak value and does not increase any more₃The air inlet valve is used for closing the Cs source, closing the light source and finishing the first activation;

step 5, heating the GaAs photocathode at low temperature;

and 6, starting the light source for secondary activation, starting the Cs source and the Li source, starting the photocurrent to rise, closing the Li source when the photocurrent reaches a first peak value, converting the photocurrent into the photocurrent to fall, and starting NF when the photocurrent falls to 40-60% of the first peak value current₃The photocurrent rises again through the air inlet valve;

step 7, when the photocurrent rises to about 3 times of the first peak current, turning on a Li source, turning off the Li source after turning on the Li source for 2-5 min, when the photocurrent rises to about 6 times of the first peak current, turning off the Li source when the photocurrent drops to 60-80% of the previous peak current, turning on the Li source when the photocurrent increase rate slows down until reaching the peak value, and turning off the Li source when the photocurrent drops to 60-80% of the previous peak current;

step 8, turning off NF when the peak value of the photocurrent is not increased any more₃And (4) an air inlet valve, a Cs source is closed, a light source is closed, and activation is finished.

2. The activation method for improving the stability of the GaAs photocathode according to claim 1, wherein the chemical cleaning method in the step 1 is specifically:

carrying out ultraviolet ozone cleaning on the surface of the GaAs photocathode;

removing grease on the surface of the GaAs photoelectric cathode;

putting the GaAs photocathode into an HF solution for etching;

putting the GaAs photocathode into a mixed solution of hydrochloric acid and isopropanol for etching;

washing the GaAs photocathode clean by using deionized water;

and drying the cleaned GaAs photocathode by using nitrogen.

3. The activation method for improving the stability of the GaAs photocathode according to claim 1, wherein the high temperature purification step in step 1 is: and (3) putting the photocathode subjected to chemical cleaning into an ultrahigh vacuum system for heating for 40-80 minutes at the temperature of 550-650 ℃.

4. The activation method for improving the stability of the GaAs photocathode according to claim 1, characterized in that the high temperature purification step in step 6 is: and (3) putting the photocathode after the first activation into an ultrahigh vacuum system to heat for 10-20 minutes, wherein the heating temperature is 450-550 ℃.

5. The activation method for improving the stability of GaAs photocathode according to claim 1, wherein the Cs source and the Li source are solid sources packaged by a nickel tube, the Cs source is a solid source of Cs for reducing chromic acid from zirconium-aluminum alloy powder, the Li source is a solid source of Li for reducing chromic acid from zirconium-aluminum alloy powder, and NF is₃The source is a high purity gaseous source.

6. The activation method for improving the stability of GaAs photocathode according to claim 1, wherein the high temperature cleaning and the activation are both performed in an ultra-high vacuum systemThe vacuum degree of the system is not lower than 10^-7Of the order of Pa.

Technical Field

The invention belongs to a GaAs photocathode activation technology, and particularly relates to an activation method for improving the stability of a GaAs photocathode.

Background

The GaAs photocathode is an important component of a modern low-light-level night vision device, and has wide application in the fields of low-light-level image intensifiers, transmission electron microscopes, novel solar cells and the like. In the current photocathode application, the low stability of the GaAs photocathode is a technical problem, and the practical development of the GaAs photocathode is hindered. Therefore, how to prepare a high-stability GaAs photocathode becomes crucial. The activation process under the ultrahigh vacuum environment determines the performance of the GaAs photocathode to a great extent, and factors such as the types of the activation sources, the alternating sequence of the activation sources, the flow ratio of the activation source gas and the like in the activation process have great influence on the stability of the photocathode.

In the current GaAs photocathode activation process, a Cs/O high-temperature and low-temperature two-step activation process is most commonly used. In an ultrahigh vacuum environment, firstly, carrying out first Cs/O alternate activation on the surface of the GaAs photocathode after chemical cleaning and high-temperature purification, and then carrying out second Cs/O alternate activation on the surface of the GaAs photocathode after low-temperature purification. When the GaAs photocathode is activated, a white light source is adopted to irradiate the surface of the cathode, and Cs/O activation enables the potential barrier of the surface of the GaAs photocathode to be reduced, so that the negative electron affinity photocathode is obtained. However, the GaAs photocathode obtained by the high-temperature and low-temperature two-step activation method is poor in stability, and the second activation is slightly improved in stability compared with the first activation.

Disclosure of Invention

The invention aims to provide an activation method for improving the stability of a GaAs photocathode.

The technical solution for realizing the purpose of the invention is as follows: an activation method for improving the stability of a GaAs photocathode comprises the following specific steps:

step 1, carrying out chemical cleaning and high-temperature purification on a GaAs photoelectric cathode;

step 2, turning on a light source and carrying out first activation; turning on a Cs source and a Li source, and starting the photocurrent to rise;

and 3, turning off the Li source when the photocurrent reaches a first peak value, turning down the photocurrent, and turning on NF when the photocurrent is reduced to 40-60% of the first peak value₃The photocurrent rises again through the air inlet valve;

step 4, turning on the Li source when the photocurrent rises to about 3 times of the first peak current, and turning off the Li source when the photocurrent drops to 60-80% of the previous peak current; when the photocurrent rises to about 6 times of the first peak current, the Li source is turned on, and when the photocurrent drops to 60-80% of the previous peak current, the Li source is turned off;

step 5, turning off NF when the peak value of the photocurrent is not increased any more₃The air inlet valve is used for closing the Cs source, closing the light source and finishing the first activation;

step 6, performing secondary high-temperature purification on the GaAs photocathode;

and 7, turning on the light source, activating for the second time, turning on the Cs source and the Li source, starting the photocurrent to rise, turning off the Li source when the photocurrent reaches a first peak value, turning the photocurrent to fall, and turning on NF when the photocurrent falls to 40-60% of the first peak value₃The photocurrent rises again through the air inlet valve;

step 8, when the photocurrent rises to about 3 times of the first peak current, turning on a Li source, turning off the Li source after turning on the Li source for 2-5 min, when the photocurrent rises to about 6 times of the first peak current, turning off the Li source when the photocurrent drops to 60-80% of the previous peak current, turning on the Li source when the photocurrent increase rate slows down until reaching the peak value, and turning off the Li source when the photocurrent drops to 60-80% of the previous peak current;

step 9, turning off NF when the peak value of the photocurrent is not increased any more₃And (4) an air inlet valve, a Cs source is closed, a light source is closed, and activation is finished.

Preferably, the chemical cleaning method in step 1 specifically comprises:

carrying out ultraviolet ozone cleaning on the surface of the GaAs photocathode;

removing grease on the surface of the GaAs photoelectric cathode;

putting the GaAs photocathode into an HF solution for etching;

putting the GaAs photocathode into a mixed solution of hydrochloric acid and isopropanol for etching;

washing the GaAs photocathode clean by using deionized water;

and drying the cleaned GaAs photocathode by using nitrogen.

Preferably, the high-temperature purification step in step 1 is: and (3) putting the photocathode subjected to chemical cleaning into an ultrahigh vacuum system for heating for 40-80 minutes at the temperature of 550-650 ℃.

Preferably, the high-temperature purification step in step 6 is: and (3) putting the photocathode after the first activation into an ultrahigh vacuum system to heat for 10-20 minutes, wherein the heating temperature is 450-550 ℃.

Preferably, the Cs source and the Li source are both solid sources packaged by nickel tubes, the Cs source is a solid source for reducing the Cs chromate from the zirconium-aluminum alloy powder, the Li source is a solid source for reducing the Li chromate from the zirconium-aluminum alloy powder, and NF is₃The source is a high purity gaseous source.

Preferably, the vacuum degree of the ultrahigh vacuum system is not lower than 10^-7Of the order of Pa.

Compared with the prior art, the invention has the following remarkable advantages:

1. the GaAs photocathode activated by the method has higher stability;

2. the operation method is simple and easy to realize;

3. the method has less operation steps, the Cs source is always kept in an open state, and the opening and closing of the Li source only need to judge the magnitude of photocurrent, NF₃The opening and closing of the photoelectric cathode can be realized by only controlling the valve switch, the operability is high, and the stability of the photoelectric cathode is obviously improved.

Drawings

FIG. 1 is a flow chart of the present invention.

FIG. 2 shows the Cs/Li/NF ratio of the invention after high temperature heating₃Photocurrent curve of the activated GaAs photocathode.

FIG. 3 shows Cs/Li/NF after low temperature heating in accordance with the present invention₃Photocurrent curve of the activated GaAs photocathode.

FIG. 4 shows activation and Cs/NF of the present invention₃Graph of activated GaAs photocathode photocurrent decay versus time.

Detailed Description

As shown in FIG. 1, an activation method for improving the stability of GaAs photocathode comprises two Cs/Li/NF₃And (4) activating, wherein activation is carried out once after two times of high-temperature purification respectively. The method comprises the following specific steps:

step 1, chemically cleaning a GaAs photoelectric cathode, and putting the GaAs photoelectric cathode into an ultrahigh vacuum system for high-temperature purification;

the chemical cleaning method comprises the following steps: firstly, carrying out ultraviolet ozone cleaning on the surface of a GaAs photocathode, then removing grease on the surface of the GaAs photocathode, secondly, sequentially putting the GaAs photocathode into HF solution and mixed solution of hydrochloric acid and isopropanol for etching, then, washing the GaAs photocathode clean by using deionized water, and finally, drying the cleaned GaAs photocathode by using nitrogen.

The high-temperature purification step is as follows: and (3) putting the photocathode subjected to chemical cleaning into an ultrahigh vacuum system for heating for 40-80 minutes at the temperature of 550-650 ℃.

Step 2, turning on a Cs source and a Li source, starting the photocurrent to rise, turning off the Li source when the photocurrent reaches a first peak value, turning the photocurrent to fall, and turning on the NF of the ultra-high vacuum system when the photocurrent falls to 40% -60% of the first peak value current₃The photocurrent rises again through the air inlet valve;

step 3, turning on the Li source when the photocurrent rises to about 3 times of the first peak current, and turning off the Li source when the photocurrent drops to 60-80% of the previous peak current; when the photocurrent rises to about 6 times of the first peak current, the Li source is turned on, and when the photocurrent drops to 60-80% of the previous peak current, the Li source is turned off;

step 4, turning off NF when the peak value of the photocurrent is not increased any more₃The air inlet valve closes the Cs source, closes the light source, finishes the first activation and activates a photocurrent curve as shown in figure 2;

step 5, performing secondary high-temperature purification on the GaAs photocathode;

the high-temperature purification step is as follows: and (3) putting the photocathode after the first activation into an ultrahigh vacuum system to heat for 10-20 minutes, wherein the heating temperature is 450-550 ℃.

And 6, turning on the Cs source and the Li source, starting the photocurrent to rise, turning off the Li source when the photocurrent reaches a first peak value, turning the photocurrent to fall, and turning on NF when the photocurrent falls to 40-60% of the first peak value current₃The photocurrent rises again through the air inlet valve;

step 7, when the photocurrent rises to about 3 times of the first peak current, turning on a Li source, turning off the Li source after turning on the Li source for 2-5 min, when the photocurrent rises to about 6 times of the first peak current, turning off the Li source when the photocurrent drops to 60-80% of the previous peak current, turning on the Li source when the photocurrent increase rate slows down until reaching the peak value, and turning off the Li source when the photocurrent drops to 60-80% of the previous peak current;

step 8, turning off NF when the peak value of the photocurrent is not increased any more₃The inlet valve, the Cs source off, the light source off, the end of activation, and the activation photocurrent curve are shown in fig. 3.

The above reactions are all carried out in an ultrahigh vacuum system, and the vacuum degree of the ultrahigh vacuum system is not less than 10^-7Of the order of Pa. During the activation process, a tungsten halogen lamp is used to vertically irradiate the cathode surface. The used Cs source and Li source are solid sources packaged by nickel tubes, the Cs source is a solid source of reducing chromic acid Cs from zirconium-aluminum alloy powder, the Li source is a solid source of reducing chromic acid Li from zirconium-aluminum alloy powder, and NF₃The source is a high purity gaseous source.

As can be seen from fig. 4, the GaAs photocathode activated by the present invention has better stability.