CN115020169A - Method for controlling negative electron affinity of NEA GaN photocathode in real time - Google Patents

Method for controlling negative electron affinity of NEA GaN photocathode in real time Download PDF

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CN115020169A
CN115020169A CN202210532168.1A CN202210532168A CN115020169A CN 115020169 A CN115020169 A CN 115020169A CN 202210532168 A CN202210532168 A CN 202210532168A CN 115020169 A CN115020169 A CN 115020169A
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electron affinity
negative electron
temperature
deviation
nea
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王晓晖
王振营
张一帆
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Yangtze River Delta Research Institute of UESTC Huzhou
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Abstract

The invention provides a method for controlling negative electron affinity of an NEA GaN photocathode in real time, which comprises the following steps: establishing a formula model for temperature calibration; obtaining the polarizability of the adsorbed atoms of the active layer of the sample, the dipole moment formed by the atoms of the active layer and the atoms of the emitting layer and the temperature T 0 Measuring T a plurality of times 0 Negative electron affinity χ under conditions 0 Fitting sample parameters according to the data; substituting the sample parameters and the target negative electron affinity χ into the formula model, and calculating the output temperature T 1 (ii) a Measurement of T 1 Negative electron affinity χ under conditions 1 And determine χ 1 Degree of deviation s of 1 If it is less than the set value, the output temperature T is equal to T 1 If not less than the set value, then at T 1 According to x under the condition 1 Fitting the sample parameters again; calculating the output temperature T again according to the new x 2 (ii) a Measurement of T 2 Negative electron affinity χ under conditions 2 And comparing the degrees of deviation s 2 And a set point. Repeating the above steps until the deviation s n When the temperature is less than the set value, the cycle is ended, and the optimal temperature T which corresponds to chi is output n . The invention can realize real-time accurate control of negative electron affinity of the NEA GaN photocathode by a self-calibration temperature method, and has the advantages of improving performance parameters such as quantum efficiency and stability and improving working performance of the NEA GaN photocathode.

Description

Method for controlling negative electron affinity of NEA GaN photocathode in real time
Technical Field
The invention relates to the measurement and adjustment of GaN photocathode negative electron affinity parameters, in particular to a method for controlling NEA GaN photocathode negative electron affinity in real time.
Technical Field
The photocathode is a photoelectric emission material that converts an optical signal into an electrical signal using an external photoelectric effect. In recent years, with the development and improvement of GaN material preparation technology and p-type doping technology, GaN photocathodes are becoming a novel high-performance photocathode. GaN is a third-generation semiconductor material, has the advantages of wide forbidden band, high quantum efficiency, good stability, radiation resistance, corrosion resistance and the like, has the characteristics of forbidden band width, is suitable for manufacturing devices such as light-emitting devices or light detectors, and has very wide and important application in the aspects of electron sources and the like.
To obtain efficient photoemission from GaN photocathodes, it is necessary to have a Negative Electron Affinity (NEA) characteristic, i.e., to reduce the vacuum level at the GaN emission surface below the in vivo conduction band bottom level. The NEA GaN surface can be obtained by an active layer of Cs alone or collectively capped with an active layer of Cs/O. A GaN photocathode that obtains NEA characteristics can be used as an electron source, and the transport process of photo-excited electrons to the cathode surface is complicated. Spicer proposes a "three-step model" of photocathode photoemission: the first step is the absorption of light: under the irradiation of ultraviolet light below 365nm, valence band electrons absorb the energy of incident photons and are excited to a conduction band; the second step is the transportation of the excited electrons to the surface of the cathode; the third step is the escape of electrons: electrons moving to the cathode surface tunnel through the surface barrier and due to the NEA character they escape easily into the vacuum. The above process has many parameters, wherein the difference between the vacuum level and the conduction band bottom level of the GaN material in the third step, namely the magnitude of the negative electron affinity, is an important parameter for measuring the characteristics of the GaN photocathode, and the value can influence the quantum efficiency.
In practical applications, in order to improve the stability of the cathode material, it is often necessary for the electron source to achieve a specific quantum efficiency or to maintain a specific quantum efficiency. The above object can be achieved by adjusting the magnitude of the negative electron affinity, and therefore, the measurement and control of the negative electron affinity are extremely important.
Disclosure of Invention
The invention aims to provide a method capable of controlling the negative electron affinity of an NEA GaN photocathode in real time, which realizes real-time accurate control of the negative electron affinity of the NEA GaN photocathode by a method of self-calibration temperature, is simple and convenient to operate, and has obvious advancement compared with the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the method for controlling the negative electron affinity of the NEA GaN photocathode in real time provided by the invention comprises the following steps of firstly establishing a formula model for calibrating the negative electron affinity and the temperature of the NEA GaN photocathode, wherein the formula model comprises the following components:
Figure BDA0003646331600000011
wherein p is the distance between dipoles formed between adatoms; alpha is alpha ad Is the adatom polarizability. Epsilon 0 Is the vacuum dielectric constant ε 0 ＝8.854×10 -12 F/m; e is the charge amount of electrons, e is 1.6 × 10 -19 C and T are absolute temperatures.
The method for controlling the negative electron affinity of the NEA GaN photocathode in real time provided by the invention comprises the following steps after the establishment of the formula model is completed:
(1) determining the target negative electron affinity χ of the NEA GaN photocathode sample before the experiment begins;
(2) obtaining the temperature T under initial experimental conditions 0 Measuring T a plurality of times 0 Negative electron affinity χ of NEA GaN photocathode under condition 01 ,χ 02 ,χ 03 ,...,χ 0n ；
(3) Substituting the negative electron affinity χ of the sample target into a formula model to calculate the output temperature T 1 ；
(4) Measurement of T 1 Negative electron affinity χ of NEA GaN photocathode under condition 11 ,χ 12 ,χ 13 ,...,χ 1n Acquiring m groups of data and calculating χ 1 Degree of deviation s of 1 ；
(5) Determining x 1 Degree of deviation s of 1 If it is less than the set value, the output temperature T is equal to T 1 If not less than the set value, then at T 1 Fitting the sample parameters again according to the obtained data under the condition;
(6) substituting the new sample target negative electron affinity χ into the formula model again to calculate the output temperature T 2 ；
(7) Multiple measurement of T 2 Negative electron affinity χ under conditions 21 ，χ 22 ,χ 23 ,...,χ 2n And continue to compare χ 2 Degree of deviation s of 2 The magnitude relation with the set value;
(8) repeating the above process of measuring, calculating and judging until the value of χ n Deviation from χ s n When the temperature is less than the set value, the cycle is ended, and the optimal temperature T which corresponds to chi is output n 。
Further, the target negative electron affinity χ is a value which needs to be achieved in actual work, and the value of χ is in the range of-0.5 to-1.0 in view of existing data;
further, the deviation set value s is set according to the accuracy degree of the actual requirement, and the value of s is generally in the range of 0 to 0.1%;
furthermore, the m groups of data are negative electron affinity samples under a certain temperature condition, and the sample amount is at least 50 groups because 1 sample parameter related to the temperature exists in the formula model established by the invention;
further, the deviation s in the step (4), the step (7) and the step (8) n The calculation model of (a) is:
Figure BDA0003646331600000021
wherein n is the data sequence number, χ n Representing the number of samples of acquired m sets of negative electron affinities, m being the number of samples of said negative electron affinities, and χ being the target negative electron affinity.
Further, the data generated in the above experimental steps can be used as the reference value initially set in the next experiment.
Further, the method can accurately control the negative electron affinity of the working NEA GaN photocathode in real time on line.
Furthermore, the measurement and calibration processes are automatically carried out by computer software and hardware, only the target negative electron affinity χ, the deviation set value s and the measurement sample number m need to be input, and the optimal temperature T ═ T can be output finally in the experiment n And actual degree of deviation s n 。
The invention has the advantages and beneficial effects that:
(1) the method greatly meets different requirements on the NEA GaN photocathode negative electron affinity and the quantum efficiency in any experiment or application scene.
(2) The real-time accurate control of the negative electron affinity greatly improves the stability and durability of the NEA GaN photocathode material, and effectively improves the working performance of the NEA GaN photocathode.
(3) The device is simple, the operation is simple and convenient, the adverse factors are few, and the required cost is low.
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FIG. 1 is a flow chart of the method of the present invention.
Detailed Description
The present invention is further described in detail with reference to the following embodiments in order to explain technical features and advantages of the present invention more deeply. The specific embodiments of the present invention are merely illustrative of the present invention and should not be construed as limiting the scope of the present invention in any way.
Method flow diagram of the invention as shown in fig. 1, there are many possible ways of implementing the flow diagram, and the present application only gives two specific examples by way of example.
Example one
In this embodiment, a thickness of 200nm and a doping concentration of 3.0 × 10 are selected 17 cm -3 And pure GaN material with doping element Mg, size of 10 × 10mm and substrate sapphire.
In this embodiment, after the establishment of the temperature calibration formula model is completed, the following specific steps are performed:
(1) determination of the sample doping concentration n before the start of the experiment A Is 3.0X 10 17 cm -3 The wavelength lambda of the working incident light is 230nm, and the two parameters are fixed and unchanged in the next experiment after being determined; setting the target negative electron affinity chi to be-0.8 and the deviation set value s to be 0.04 percent;
(2) obtaining the temperature T under initial experimental conditions 0 Measured as T 0 320K and measure the temperature T 0 The NEA GaN photocathode negative electron affinity under the condition of 320K is taken as a data sample, and 50 groups of data chi are recorded 01 ＝-0.7314,χ 02 ＝-0.7326,...,χ 050 ＝-0.7433；
(3) Inputting the sample with negative electron affinity χ -0.8 into a formula model, and calculating the output temperature T 1 ＝312K；
(4) Measuring the temperature T 1 The NEA GaN photocathode negative electron affinity under the condition of 320K is taken as a data sample, and 50 groups of data chi are recorded 11 ＝-0.7716,χ 12 ＝-0.7728,..,χ 150 ＝-0.7817；
(5) Calculating chi 1 Degree of deviation s of 1 The result of the calculation is s 1 When it is 1.1575%, s is judged 1 Not less than s at a temperature T 1 312K according to the 50 groups of data (χ) obtained in the last step 11 ＝-0.7716,χ 12 ＝-0.7728,..,χ 150 -0.7817), calculating the output temperature T in combination with the target negative electron affinity χ -0.8 2 The result of the calculation is T 2 ＝308K；
(6) Measuring the temperature T 2 The negative electron affinity under the condition of 308K is taken as a data sample, and 50 groups of data χ are recorded 21 ＝-0.7814,χ 21 ＝-0.7827,...,χ 250 -0.7911, and continue to compare χ 2 Degree of deviation s of 2 The magnitude relation between 0.1425% and a deviation set value s;
(7) repeating the above process of measuring, calculating and judging until the 5 th test, and calculating T by combining the existing data and formula model 6 301K and at a temperature T 6 Measuring 50 groups under the condition of 301KAccording to chi 61 ＝-0.7911,χ 62 ＝-0.7925,...,χ 650 -0.7894, obtained as χ 6 Deviation from χ s 6 When the value is equal to 0.0341%, s is determined 6 When the deviation set value s is less than 0.04%, the cycle is ended, and the optimal temperature T corresponding to χ is output as 301K.
Specifically, the deviation s in step (4), step (6) and step (7) n The calculation model of (a) is:
Figure BDA0003646331600000031
wherein n is the data sequence number χ n Representing the acquired 50 sets of electron escape probability samples.
Specifically, the data generated in the above experimental steps can be used as the reference value initially set in the next experiment.
Specifically, the method can accurately control the negative electron affinity of the working NEA GaN photocathode in real time on line.
Specifically, the above measurement and calibration processes are automatically performed by computer software and hardware, and only the target negative electron affinity χ -0.8, the deviation set value s-0.04%, and the obtained sample number m-50 need to be input, and the final output optimal temperature T301K and the actual deviation s of the experiment are obtained 6 ＝0.0341％。
Example two
In this embodiment, a thickness of 200nm and a doping concentration of 2.1 × 10 are selected 18 cm -3 And pure GaN material with doping element Mg, size of 10 × 10mm and substrate sapphire.
After the temperature calibration formula model of the present invention is established, the following steps are performed:
(1) determination of the sample doping concentration n before the start of the experiment A Is 2.1 × 10 18 cm -3 The wavelength lambda of the working incident light is 300nm, and the two parameters are fixed and unchanged in the next experiment after being determined; setting the target negative electron affinity chi to be-1.0 and the deviation set value s to be 0.01 percent;
(2) obtaining initial realityTemperature T under test conditions 0 Measured as T 0 300K and measuring the temperature T 0 The negative electron affinity of the NEA GaN photocathode under the condition of 300K is taken as a data sample, and 100 groups of data chi are recorded 01 ＝-0.8417,χ 02 ＝-0.8433,...,χ 0100 ＝-0.8465；
(3) Inputting the sample with negative electron affinity χ -1.0 into a formula model, and calculating the output temperature T 1 ＝293K；
(4) Measuring the temperature T 1 The NEA GaN photocathode negative electron affinity under 293K condition was used as a data sample, and 100 sets of data χ were recorded 11 ＝-0.8672,χ 12 ＝-0.8683,..,χ 1100 ＝-0.8733；
(5) Calculating chi 1 Degree of deviation s of 1 The result of the calculation is s 1 When it is 1.1453%, s is judged 1 Not less than s at a temperature T 1 293K according to 100 sets of data (χ) obtained in the previous step 11 ＝-0.8672,χ 12 ＝-0.8683,..,χ 1100 -0.8733) is calculated in combination with a target negative electron affinity χ -1.0 2 The result of the calculation is T 2 ＝285K；
(6) Measuring the temperature T 2 Record 100 sets of data χ as data sample with negative electron affinity under 285K condition 21 ＝-0.8937,χ 22 ＝-0.8945,...,χ 2100 -0.8986, and continue to compare χ 2 Degree of deviation s of 2 0.1366% and a deviation set value s;
(7) repeating the above process of measuring, calculating and judging until the 5 th test, and calculating T by combining the existing data and formula model 6 277K at a temperature T 6 100 groups of data χ are measured under the condition of 277K 61 ＝-0.9813,χ 62 ＝-0.9863,...,χ 6100 0.9975 to give χ 6 Deviation from χ s 6 When the average value is 0.0097%, s is judged 6 When the deviation set value s is less than 0.01%, the cycle is ended, and the optimal temperature T corresponding to chi is output at 277K.
Specifically, the steps (4), (6) and (7)Degree of deviation s n The calculation model of (a) is:
Figure BDA0003646331600000041
wherein n is the data sequence number χ n Representing 100 samples of electron escape probability obtained.
Specifically, the data generated in the above experimental steps can be used as the reference value initially set in the next experiment.
Specifically, the method can accurately control the negative electron affinity of the working NEA GaN photocathode in real time on line.
Specifically, the above measurement and calibration processes are automatically performed by computer software and hardware, and only the target negative electron affinity χ -1.0, the deviation set value s-0.01%, and the obtained sample number m-100 need to be input, and the final output optimal temperature T-277K and the actual deviation s of the experiment are obtained 6 ＝0.0097％。
While particular embodiments of the present invention have been shown and described, the present invention is not limited by the foregoing embodiments. Those skilled in the art will appreciate that various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the spirit and scope of the invention, and that such changes fall within the scope of the claimed invention. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (8)

1. A method for controlling NEA GaN photocathode negative electron affinity in real time is characterized in that a formula model for calibration of NEA GaN photocathode negative electron affinity and temperature is established, and the formula model is as follows:
Figure FDA0003646331590000011
wherein p is the distance between dipoles formed between adatoms; alpha is alpha ad Is the adatom polarizability. Epsilon 0 Is the vacuum dielectric constant ε 0 ＝8.854×10 -12 F/m; e is the charge amount of electrons, e is 1.6 × 10 -19 C and T are absolute temperatures.
2. The method of claim 1 wherein said formulaic model is constructed by the steps of:
(1) setting a target negative electron affinity χ and a deviation set value s;
(2) obtaining a temperature T 0 Measuring T a plurality of times 0 Negative electron affinity χ under conditions 0 Fitting sample parameters according to the obtained m groups of data;
(3) substituting the target negative electron affinity χ of the sample and the sample parameter into a formula model, and calculating the output temperature T 1 ；
(4) Multiple measurement of T 1 Negative electron affinity χ of NEA GaN photocathode under condition 1 Obtaining m groups of data, calculating χ 1 Degree of deviation s of 1 ；
(5) Determining the degree of deviation s 1 If s is less than the set value s 1 If less than s, the output temperature T is equal to T 1 If not, at T 1 Under the condition, fitting the sample parameters again according to the obtained m groups of data;
(6) calculating the output temperature T by combining the new sample parameter and the target negative electron affinity chi 2
(7) Measuring T 2 Negative electron affinity under conditions P 2 And continue to compare P 2 Degree of deviation s of 2 And the magnitude of the set value;
(8) repeating the steps (5) to (7) until the x value is reached n Deviation from χ s n When the temperature is less than the set value, the circulation is ended, and the optimal temperature T which corresponds to chi is output n 。
3. The method of claim 2, wherein the target negative electron affinity χ is a value that is actually needed for operation; the deviation degree set value s is set according to the accuracy degree of the actual requirement; the m groups of data are acquired negative electron affinity samples under certain temperature conditions.
4. The method of claim 2, wherein the fitting process in step (2) and step (5) is: using m sets of measured data (χ) n ,T n ) And fitting the formula model to obtain a fitting result of the negative electron affinity χ of the sample.
5. The method of claim 2, wherein the deviation s in step (4), step (7) and step (8) is a measure of the negative electron affinity of the NEA GaN photocathode in real time n The calculation model of (a) is:
Figure FDA0003646331590000012
wherein n is the data sequence number χ n Representing m groups of negative electron affinity samples obtained, m being the number of samples of the negative electron affinity, and χ being the target negative electron affinity.
6. The method of claim 2 wherein the data generated in the experimental step is used as a reference value initially set for the next experiment.
7. The method of claim 2 wherein the method allows real-time on-line precise control of the negative electron affinity of an operating NEA GaN photocathode.
8. The method of claim 2 in which the measurement and calibration are performed automatically by computer software and hardware, requiring only input of the target negative electron affinity χ, of,The deviation set value s and the number m of the measurement samples are enough, and the optimal temperature T and the actual deviation s can be finally output in the experiment n 。
CN202210532168.1A 2022-05-16 2022-05-16 Method for controlling negative electron affinity of NEA GaN photocathode in real time Pending CN115020169A (en)

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