CN109427518B - Activation method for improving quantum efficiency and service life of GaAs photocathode - Google Patents
Activation method for improving quantum efficiency and service life of GaAs photocathode Download PDFInfo
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- CN109427518B CN109427518B CN201710782391.0A CN201710782391A CN109427518B CN 109427518 B CN109427518 B CN 109427518B CN 201710782391 A CN201710782391 A CN 201710782391A CN 109427518 B CN109427518 B CN 109427518B
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- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
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Abstract
The invention discloses an activation method for improving the quantum efficiency and the service life of a GaAs photocathode, namely, in an ultrahigh vacuum activation system, a monochromatic light source with the wavelength of 532nm is adopted to replace the traditional halogen dock lamp light source for activation. The activation steps comprise: 1. chemically cleaning a GaAs sample to be activated; 2. purifying the sample after chemical cleaning at high temperature; 3. and (3) irradiating the surface of the cathode by adopting a monochromatic light source with the wavelength of 532nm, and activating the sample by adopting a continuous Cs source and intermittent oxygen source process. The GaAs photocathode obtained by the method is obviously improved in quantum effect and stability.
Description
Technical Field
The invention relates to a method for activating by adopting monochromatic light in the process of preparing a negative electron affinity semiconductor photoelectric emission material, in particular to an activation method capable of improving the quantum effect and the service life of a GaAs photoelectric cathode.
Background
The gallium arsenide (GaAs) photocathode is used as a negative electron affinity photocathode, can convert weak optical signals which are difficult to distinguish by naked eyes into electric signals, and has good photoelectric property and wide prospect. In order to obtain high quantum effects and long lifetime, it has extremely high requirements on the degree of vacuum and surface cleaning of the production process and the production equipment. As far as now is concerned, there is still a need for further improvement of the stability of the cathode, i.e. to minimize the rate of decay of the quantum efficiency of the cathode over time. The stability of the GaAs photocathode mainly depends on the interaction between the surface activation layer and the GaAs surface, and whether the surface activation layer fails is closely related to the factors such as the system vacuum degree, the type and purity of an activation source, the surface activation process and the like, so that the research and development of the activation process capable of prolonging the service life of the GaAs photocathode has important significance for the research and development of a high-performance micro-optical image intensifier.
The illumination condition is an important factor in the activation process, and can influence the adsorption effect of Cs and O on the surface of the cathode to a great extent, so that the quantum effect and the service life of the GaAs photocathode are influenced. In the conventional activation method, a tungsten halogen lamp with an illuminance of 100 lux is generally used to vertically irradiate the cathode surface. However, the GaAs photocathode obtained by using the tungsten halogen lamp as the activation method under the illumination condition still has a large space for improving the quantum effect and stability, and is not satisfactory especially in the life of the cathode.
Disclosure of Invention
The invention aims to provide an activation method using monochromatic light as illumination conditions, which can enable a GaAs photocathode to have higher quantum efficiency and stability.
The technical solution for realizing the purpose of the invention is as follows: an activation method for improving the quantum efficiency and the service life of a GaAs photocathode comprises the following steps:
step 2, performing high-temperature purification on the sample after chemical cleaning;
step 4, the photocurrent reaches a peak value and is reduced, the oxygen source is opened when the photocurrent is reduced to 75% -85% of the peak value, and the oxygen source is closed when the photocurrent has a new peak value;
and 5, repeating the step 4 until the peak current of the photocurrent is not increased any more, successively closing the oxygen source and the cesium source, and ending the activation process.
Compared with the prior art, the invention has the beneficial effects that: 1) compared with the traditional activation method, the increase speed of the photocurrent of the monochromatic light irradiation activation is faster than that of the tungsten halogen lamp irradiation activation, and higher cathode quantum efficiency can be obtained; 2) the GaAs photocathode obtained by the activation method provided by the invention has longer service life, and the stability after Cs is supplemented is higher than that of the traditional method.
Drawings
Fig. 1 is an activation flow diagram of the present invention.
Fig. 2 is a graph showing the variation of photocurrent on the surface of a sample during activation according to the present invention and the conventional method.
FIG. 3 is a graph comparing the quantum effect curves of GaAs cathode samples activated by the present invention and conventional methods.
Fig. 4 is a graph comparing the photocurrent decay of GaAs cathode samples after activation according to the present invention and the conventional method.
FIG. 5 is a comparison graph of the quantum effect curves after the GaAs cathode sample is compensated with Cs after being activated by the method of the present invention and the conventional method.
FIG. 6 is a graph showing the photocurrent attenuation comparison after the GaAs cathode sample is compensated with Cs after being activated by the method of the present invention and the conventional method.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments.
With reference to fig. 1, the activation method for improving the quantum efficiency and the lifetime of the GaAs photocathode of the present invention includes the following steps:
Step 2, performing high-temperature purification on the sample after chemical cleaning; the high-temperature purification step is as follows: delivering the sample after chemical cleaning to a heating position of an activation system for heating, wherein the heating temperature is 650 ℃, the heating time is 10 minutes, and the vacuum degree of the system is not less than 1 multiplied by 10 in the heating process-6Pa。
step 4, the photocurrent reaches a peak value and is reduced, the oxygen source is opened when the photocurrent is reduced to 75% -85% of the peak value, and the oxygen source is closed when the photocurrent has a new peak value;
and 5, repeating the step 4 until the peak current of the photocurrent is not increased any more, successively closing the oxygen source and the cesium source, and ending the activation process.
The step 3, the step 4 and the step 5 are all carried out in an ultrahigh vacuum system, and the vacuum degree of the ultrahigh vacuum system is not lower than 10-7Of the order of Pa.
The GaAs photocathode obtained by the method is obviously improved in quantum effect and stability.
The present invention will be described in further detail with reference to examples.
Examples
Before cesium oxygen activation, we performed chemical cleaning and high temperature purification of GaAs photocathode materials.
The chemical washing step is carried out by first placing the sample in a container containing a predetermined amount of CCl4And then placing the beaker into an ultrasonic cleaner to vibrate for 5min, taking out the sample, and then respectively placing the sample into acetone, ethanol and deionized water to clean according to the same method. And then placing the sample into an HF solution for standing and cleaning for 5min, and finally repeatedly washing and drying the sample by deionized water.
The high-temperature purification step is to heat the sample at 650 deg.C for 10 min and to maintain the vacuum degree of the system at not less than 1 × 10-7Pa, so as to avoid the secondary pollution of the vacuum residual gas to the sample when the temperature is reduced. After heating, cesium oxygen activation begins when the sample is naturally cooled to about 30 ℃.
During activation, a monochromatic light source with the wavelength of 532nm is used for vertically irradiating the cathode surface, and the on or off of the cesium source and the oxygen source is determined by measuring and observing the photocurrent generated by the cathode in real time. And the cesium source and the oxygen source used for activation are solid sources packaged by nickel tubes, wherein the cesium source is a solid source for reducing cesium chromate by using zirconium-aluminum alloy powder, and the oxygen source is a solid source for reducing barium peroxide. The magnitude of the current of the external current source is changed through computer software, and the magnitudes of the electrification and deflation amounts of the cesium source and the oxygen source can be adjusted. Because the outgassing amount of cesium oxygen sources from different sources may be different, the current of the cesium oxygen sources used in the activation process will also be different, and a suitable cesium-oxygen ratio should be obtained through an experimental method after replacing the cesium oxygen sources, in this example, the current of the cesium source is 4.0 to 4.5 amperes, the current of the oxygen source is 1.5 to 2.0 amperes, the activation is performed by using a method in which the cesium source is continuous and the oxygen source is intermittent, and the activation steps are as follows:
(1) the cesium source is turned on and always kept in an on state, and the photocurrent gradually rises;
(2) the photocurrent reaches a peak value and is reduced, the oxygen source is opened when the photocurrent is reduced to 85 percent of the peak value, and the oxygen source is closed when the photocurrent has a new peak value;
(3) and (3) repeating the steps (1) and (2) until the peak current of the photocurrent is not increased any more, then closing the oxygen source and the cesium source in sequence, and ending the activation process.
Under the conditions of the same GaAs photocathode, the same chemical cleaning, high-temperature purification and vacuum environment, the following two groups of light sources are respectively used for irradiating the surface of the photocathode to carry out an activation experiment.
(1) A 12V/20W tungsten halogen lamp;
(2) a monochromatic light source with a wavelength of 532 nm.
The change curves of the photocurrent of the two groups of sample surfaces during the activation process are shown in fig. 2. During the first Cs feeding process, the increase speed of the photocurrent activated by the monochromatic light is faster than that activated by the irradiation of the halogen tungsten lamp. In the following Cs, O alternation, the photocurrent curve of the monochromatic light activation has fewer Cs/O alternation times. Because the illumination intensity of the halogen tungsten lamp is high, the cathode sample can absorb sufficient illumination, so that the final photocurrent of the excitation of the halogen tungsten lamp by illumination reaches 34.86 muA, and the final photocurrent of the excitation of the 532nm monochromatic light is only 0.56 muA.
Fig. 3 shows the quantum effects of two groups of GaAs photocathode samples obtained by the online test using the multiple information content test system after the activation, and the curves are normalized. As can be seen from FIG. 3, the quantum effect of the cathode sample activated by 532nm monochromatic light is higher in the long-wave band.
FIG. 4 shows the first photocurrent decay for both samples when irradiated by 100lx light from a 12V/20W tungsten halogen lamp. Although the lifetime of the cathode is generally low due to the non-ideal degree of vacuum of the system, the result shows that the GaAs photoelectric cathode sample under the activation of monochromatic light is more stable than the sample under the irradiation activation of a tungsten halogen lamp.
FIG. 5 shows the quantum effect of two groups of samples after Cs is supplemented. The cathode quantum effect after the Cs is supplemented is lower than the quantum effect after the activation. After Cs is supplemented, the quantum efficiency of the 532nm monochromatic light activated sample is higher than that of a sample activated by irradiation of a halogen tungsten lamp, and the quantum efficiency is particularly more obvious in a long-wave band.
Fig. 6 shows the decay of photocurrent after Cs supplementation for two sets of samples. After the two samples are subjected to Cs supplementation, the photocurrents are gradually reduced. However, the decay rate of the monochromatic light activated samples was much less than that of the tungsten halogen lamps irradiating the activated samples, which further demonstrates the better stability of the monochromatic light activated GaAs photocathode.
From the above, the GaAs photocathode obtained by the method of the invention has longer service life, and the stability after Cs is supplemented is higher than that of the traditional method.
Claims (4)
1. An activation method for improving the quantum efficiency and the service life of a GaAs photocathode is characterized by comprising the following steps of:
step 1, carrying out chemical cleaning on a sample to be activated;
step 2, performing high-temperature purification on the sample after chemical cleaning;
step 3, irradiating the surface of the photocathode by using a monochromatic light source with the wavelength of 532nm, starting the cesium source and keeping the cesium source in a starting state all the time, and gradually increasing the photocurrent;
step 4, the photocurrent reaches a peak value and is reduced, the oxygen source is opened when the photocurrent is reduced to 75% -85% of the peak value, and the oxygen source is closed when the photocurrent has a new peak value;
and 5, repeating the step 4 until the peak current of the photocurrent is not increased any more, successively closing the oxygen source and the cesium source, and ending the activation process.
2. The activation method for improving the quantum efficiency and the lifetime of the GaAs photocathode according to claim 1, wherein the chemical cleaning method in the step 1 is: sequentially putting the samples to be activated into a container with CCl4Acetone, ethanol and deionized water, putting the beaker into an ultrasonic cleaner, cleaning each solution for 5min, putting the beaker into an HF solution, standing and cleaning for 5min, and finally washing the sample for at least one minute by using the deionized water.
3. The activation method for improving the quantum efficiency and the lifetime of the GaAs photocathode according to claim 1, wherein the high temperature purification step in the step 2 is: delivering the sample after chemical cleaning to a heating position of an activation system for heating, wherein the heating temperature is 650 ℃, the heating time is 10 minutes, and the vacuum degree of the system is not less than 1 multiplied by 10 in the heating process-6Pa。
4. The activation method for improving the quantum efficiency and the lifetime of the GaAs photocathode as claimed in claim 1, wherein the steps 3, 4 and 5 are all performed in an ultra-high vacuum system, and the degree of vacuum of the ultra-high vacuum system is not less than 10-7Of the order of Pa.
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| CN111584328B (en) * | 2020-04-29 | 2022-09-27 | 南京理工大学 | Activation method for improving near-infrared band response of indium gallium arsenic 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 |
| CN111584326B (en) * | 2020-04-29 | 2022-09-27 | 南京理工大学 | Activation method for improving quantum efficiency of InGaAs photocathode |
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| US6798127B2 (en) * | 2002-10-09 | 2004-09-28 | Nano-Proprietary, Inc. | Enhanced field emission from carbon nanotubes mixed with particles |
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| JP2000156153A (en) * | 1998-11-17 | 2000-06-06 | Dainippon Printing Co Ltd | Manufacture of secondary electron emission film, and the secondary electron emission film |
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