CN110706989A - Cs/NF3 activation method for improving stability of GaAs photocathode - Google Patents
Cs/NF3 activation method for improving stability of GaAs photocathode Download PDFInfo
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- CN110706989A CN110706989A CN201911042061.3A CN201911042061A CN110706989A CN 110706989 A CN110706989 A CN 110706989A CN 201911042061 A CN201911042061 A CN 201911042061A CN 110706989 A CN110706989 A CN 110706989A
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Abstract
The invention relates to Cs/NF for improving the stability of GaAs photocathode3Activation methods, i.e. using a Cs source and NF in an ultra-high vacuum activation system3The sources collectively perform GaAs photocathode activation. The method comprises the following steps: 1. degreasing and cleaning the GaAs photocathode; 2. carrying out chemical etching on the GaAs photoelectric cathode; 3. performing high-temperature purification on the GaAs photocathode in an ultrahigh vacuum system; 4. the purified GaAs photocathode is subjected to Cs/NF (Cs/NF) under the illumination of monochromatic light of a red light wave band3And (4) activating. By the mode, the GaAs photocathode with higher spectral response and better stability can be obtained.
Description
Technical Field
The invention belongs to the field of semiconductorsThe technical field of preparation of bulk photoelectric emission materials, in particular to Cs/NF for improving the stability of GaAs photocathode3An activation method.
Background
The GaAs photocathode has higher response capability and smaller dark emission current in visible light and near infrared regions, and emits electron energy and an angle distribution set, so the GaAs photocathode is widely applied to the fields of low-light-level night vision imaging devices, spin-polarized electron sources, semiconductor sensitive devices and the like. Research institutions at home and abroad are constantly dedicated to researching how to improve the spectral response and the overall performance of the GaAs-based photocathode. The development of high-performance GaAs photocathodes puts high requirements on a preparation system of the photocathode. The process of preparing the photocathode is closely related to the factors such as the vacuum degree of a system, the crystal face of a cathode material, the cleaning degree, the surface adsorption condition and the like. In the current photocathode application, it is required to be able to prepare photocathodes having long working life and long storage life. The effectiveness of the NEA GaAs photocathode activation process depends on various factors such as the degree of surface purification, the source material of the activation, the activation step, the activation light conditions, and the like.
At present, the domestic use is more based on Cs/O2The GaAs photocathode activation method of alternate activation comprises adopting a Cs source to be continuously opened, and introducing O according to the change condition of a photocurrent2The activation process of (c); only if there is a source of Cs and O2Alternate activation processes of the sources take turns, and so on. Experiments have shown that these Cs/O2The GaAs photocathode obtained by the activation method has poor stability. It remains to be studied as to which activation method should be used to improve the operating life of the cathode after activation.
In summary, the prior art has a problem that the activation effect on the GaAs photocathode is not good enough.
Disclosure of Invention
1. The technical problem to be solved is as follows:
aiming at the technical problem, the invention provides a Cs/NF for improving the stability of a GaAs photocathode3The activation method adopts the way of introducing Cs and NF simultaneously3The method activates the GaAs photocathode, and can obviously improve the GaAs photocathodeStability of (2).
2. The technical scheme is as follows:
Cs/NF capable of improving stability of GaAs photocathode3An activation method, characterized by: the method comprises the following steps:
step one, putting the GaAs photocathode into an organic solvent for degreasing and cleaning.
And step two, placing the degreased GaAs photocathode into an acid solution for chemical etching.
And step three, placing the etched GaAs photocathode into an ultrahigh vacuum system for high-temperature heating purification.
And step four, after the temperature of the ultra-high temperature system is reduced to room temperature, Cs is introduced into the GaAs photocathode, and the photocurrent or quantum efficiency of the GaAs photocathode begins to increase until the first Cs peak is reached.
And step five, continuously electrifying the GaAs photoelectric cathode to enable the Cs to be excessive, continuously electrifying the Cs when the photocurrent (quantum efficiency) of the GaAs photoelectric cathode is reduced to 70- ~ 80% of the peak value of the first Cs, and simultaneously introducing NF (nitrogen-nitrogen oxide)3So that the photocurrent or quantum efficiency of the GaAs photocathode begins to increase again.
Step six, when the photocurrent or quantum efficiency of the GaAs photocathode rises to the 2 nd peak value and is kept for a period of time, the Cs source is closed, so that the photocurrent or quantum efficiency of the GaAs photocathode rises to the peak value again, and the NF is closed at the moment3And the activation is finished.
And further, the degreasing and cleaning in the first step comprises the specific process that the GaAs photocathode is sequentially placed into a container filled with carbon tetrachloride, acetone, absolute ethyl alcohol and deionized water, and meanwhile, the container filled with the organic solvent of the GaAs photocathode is placed into an ultrasonic cleaner for ultrasonic cleaning for 5 ~ 10 minutes.
Further, the chemical etching in the second step comprises the following specific steps: and (3) placing the degreased GaAs photocathode into a solution of HCl and IPA in a ratio of 1:10 for etching for not less than 5 minutes, and then washing with deionized water for not less than 10 seconds.
And further, the high-temperature heating purification in the third step comprises the specific steps of putting the GaAs photocathode after chemical etching into an ultrahigh vacuum system for heating, wherein the heating temperature is 650 ~ 660 ℃, and the heating time is 20 minutes.
Further, Cs/NF was performed in step four, step five and step six3The illumination condition during activation is 633 +/-5 nm monochromatic light.
3. Has the advantages that:
the GaAs photocathode activated by the method has better stability, longer service life and longer storage life.
Drawings
FIG. 1 shows Cs/NF of the present invention for improving GaAs photocathode stability3A flow chart of an activation method;
FIG. 2 shows Cs/NF in accordance with an embodiment of the present invention3A quantum efficiency change diagram of an activation process;
FIG. 3 shows Cs/O in accordance with an embodiment of the present invention2A quantum efficiency change diagram of an activation process;
FIG. 4 shows the vacuum sweep gas pair Cs/NF in one embodiment of the present invention3Activation and Cs/O2The quantum efficiency of the activated GaAs photocathode affects the comparative plot.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
As shown in figure 1, Cs/NF for improving stability of GaAs photocathode3An activation method, characterized by: the method comprises the following steps:
step one, putting the GaAs photocathode into an organic solvent for degreasing and cleaning.
And step two, placing the degreased GaAs photocathode into an acid solution for chemical etching.
And step three, placing the etched GaAs photocathode into an ultrahigh vacuum system for high-temperature heating purification.
And step four, after the temperature of the ultra-high temperature system is reduced to room temperature, Cs is introduced into the GaAs photocathode, and the photocurrent or quantum efficiency of the GaAs photocathode begins to increase until the first Cs peak is reached.
Step five, continuing to electrify the GaAs photoelectric cathode to enable the GaAs photoelectric cathode to be excessive, and when the photocurrent, namely the quantum efficiency of the GaAs photoelectric cathode is reduced to 70 percent ~ 80 percent of the peak value of the first Cs% while continuing to introduce Cs and NF3So that the photocurrent or quantum efficiency of the GaAs photocathode begins to increase again.
Step six, when the photocurrent or quantum efficiency of the GaAs photocathode rises to the 2 nd peak value and is kept for a period of time, the Cs source is closed, so that the photocurrent or quantum efficiency of the GaAs photocathode rises to the peak value again, and the NF is closed at the moment3And the activation is finished.
And further, the degreasing and cleaning in the first step comprises the specific process that the GaAs photocathode is sequentially placed into a container filled with carbon tetrachloride, acetone, absolute ethyl alcohol and deionized water, and meanwhile, the container filled with the organic solvent of the GaAs photocathode is placed into an ultrasonic cleaner for ultrasonic cleaning for 5 ~ 10 minutes.
Further, the chemical etching in the second step comprises the following specific steps: and (3) placing the degreased GaAs photocathode into a solution of HCl and IPA in a ratio of 1:10 for etching for not less than 5 minutes, and then washing with deionized water for not less than 10 seconds.
And further, the high-temperature heating purification in the third step comprises the specific steps of putting the GaAs photocathode after chemical etching into an ultrahigh vacuum system for heating, wherein the heating temperature is 650 ~ 660 ℃, and the heating time is 20 minutes.
Further, Cs/NF was performed in step four, step five and step six3The illumination condition during activation is 633 +/-5 nm monochromatic light.
The specific embodiment is as follows:
according to the scheme shown in FIG. 1, in Cs/NF3Before activation, the GaAs photoelectric cathode material is subjected to degreasing cleaning, chemical etching and high-temperature purification.
And the degreasing and cleaning step is to sequentially place the GaAs photocathode sample into a container containing carbon tetrachloride, acetone, absolute ethyl alcohol and deionized water, and sequentially place the container in which the GaAs photocathode sample is placed into an ultrasonic cleaner for ultrasonic cleaning for 6 minutes.
The chemical etching step is to etch for not less than 8 minutes in a 1:10 solution of HCL and IPA, and then rinse for 20s with deionized water.
The high temperature purification step is to put the sample into a vacuum degree of 10-8In an ultra-high vacuum system of Pa magnitude, the heating temperature is set to 650 ℃ and the heating time is set to 20 minutes.
When the sample is naturally cooled to room temperature, the sample is sent to an activation chamber of a vacuum system, and the Cs/NF process is started3And (4) activating.
During activation, monochromatic red light with the wavelength of 632nm is vertically irradiated on the surface of the GaAs photocathode, and the Cs source and NF are determined by measuring and observing the quantum efficiency of cathode photoemission in real time3The source is on or off. During activation, firstly, a Cs source is turned on, and the quantum efficiency of a cathode starts to increase until a first Cs peak is reached; continuously introducing Cs to make it excessive, starting to reduce quantum efficiency, when the photoelectric current is reduced to 75% of first Cs peak value, continuously introducing Cs, at the same time introducing NF3So that the quantum efficiency starts to increase again; when the quantum efficiency rises to the 2 nd peak value and keeps turning off the Cs after a period of time, the photocurrent rises to the peak value again, and the NF is turned off at the moment3And the activation process is ended. The variation curve of quantum efficiency in the activation process of the method is shown in FIG. 2
By adopting the same GaAs photocathode and the same degreasing cleaning, chemical etching and high-temperature purification processes, a comparison experiment is carried out, a Cs source is continuously opened during activation, and O is introduced according to the change condition of quantum efficiency2Cs/O of2Activation, other activation conditions and the above Cs/NF3Activation identity, Cs/O2The variation curve of quantum efficiency during activation is shown in fig. 3.
FIG. 4 shows the vacuum sweep gas vs. Cs/NF in an embodiment of the present invention3Activation and Cs/O2The quantum efficiency of the activated GaAs photocathode affects the comparative plot. Introducing common oxygen-containing residual gas O into the activated vacuum system2CO and CO2The experiment shows that Cs/NF3The activated GaAs photocathode surface has better chemical immunity to oxygen-containing residual gas, and is suitable for oxygen-containing residual gas O in a vacuum system2、CO、CO2，Cs/NF3The decay rate of the activated cathode quantum efficiency is less than Cs/O2And (3) the quantum efficiency decay rate of the activated cathode. The slower decay of the photoemission performance of the cathode obtained by the invention can be seen, which indicates that the inventionThe activated GaAs photocathode has better stability.
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. Cs/NF capable of improving stability of GaAs photocathode3An activation method, characterized by: the method comprises the following steps:
step one, putting a GaAs photocathode into an organic solvent for degreasing and cleaning;
secondly, putting the degreased GaAs photocathode into an acid solution for chemical etching;
step three, placing the etched GaAs photocathode into an ultrahigh vacuum system for high-temperature heating purification;
step four, Cs is introduced into the GaAs photocathode after the temperature of the ultra-high temperature system is reduced to room temperature, and the photocurrent or quantum efficiency of the GaAs photocathode begins to increase until the first Cs peak is reached;
and step five, continuously electrifying the GaAs photoelectric cathode to enable the Cs to be excessive, continuously electrifying the Cs when the photocurrent (quantum efficiency) of the GaAs photoelectric cathode is reduced to 70- ~ 80% of the peak value of the first Cs, and simultaneously introducing NF (nitrogen-nitrogen oxide)3So that the photocurrent or quantum efficiency of the GaAs photocathode begins to increase again;
step six, when the photocurrent or quantum efficiency of the GaAs photocathode rises to the 2 nd peak value and is kept for a period of time, the Cs source is closed, so that the photocurrent or quantum efficiency of the GaAs photocathode rises to the peak value again, and the NF is closed at the moment3And the activation is finished.
2. Cs/NF for improving GaAs photocathode stability according to claim 13An activation method, characterized by: the degreasing and cleaning process in the first step comprises the following specific steps: the GaAs photocathode is sequentially put into a container filled with carbon tetrachloride, acetone, absolute ethyl alcohol and deionized water, and simultaneously the GaAs photocathode is put into the containerThe container of organic solvent of GaAs photocathode was put into an ultrasonic cleaner for ultrasonic cleaning for 5 ~ 10 minutes.
3. Cs/NF for improving GaAs photocathode stability according to claim 13An activation method, characterized by: the chemical etching in the second step comprises the following specific steps: and (3) placing the degreased GaAs photocathode into a solution of HCl and IPA in a ratio of 1:10 for etching for not less than 5 minutes, and then washing with deionized water for not less than 10 seconds.
4. Cs/NF for improving GaAs photocathode stability according to claim 13The activation method is characterized in that the high-temperature heating purification in the third step comprises the specific steps of putting the GaAs photocathode after chemical etching into an ultrahigh vacuum system for heating, wherein the heating temperature is 650 ~ 660 ℃, and the heating time is 20 minutes.
5. Cs/NF for improving GaAs photocathode stability according to claim 13An activation method, characterized by: performing Cs/NF in the fourth step, the fifth step and the sixth step3The illumination condition during activation is 633 +/-5 nm monochromatic light.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111584327A (en) * | 2020-04-29 | 2020-08-25 | 南京理工大学 | Activation method for improving quantum efficiency of gallium arsenide photocathode |
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| CN109427517A (en) * | 2017-09-02 | 2019-03-05 | 南京理工大学 | A kind of monochromatic light exposure Activiation method improving GaAs photocathode spectral response and stability |
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Patent Citations (5)
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| FR2004044A1 (en) * | 1968-03-15 | 1969-11-14 | Philips Nv | |
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| L.B. JONES ET AL: "GALLIUM ARSENIDE PHOTOCATHODE RESEARCH AT DARESBURY LABORATORY", 《PROCEEDINGS OF IPAC2011, SAN SEBASTIÁN, SPAIN》 * |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111584327A (en) * | 2020-04-29 | 2020-08-25 | 南京理工大学 | Activation method for improving quantum efficiency of gallium arsenide photocathode |
| CN111584327B (en) * | 2020-04-29 | 2022-09-27 | 南京理工大学 | Activation method for improving quantum efficiency of gallium arsenide photocathode |
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