A method for real-time control of electron escape probability of NEA GaN photocathode

Abstract

The present invention provides a method for real-time control of the electron escape probability of NEAGaN photocathode, which specifically comprises: establishing a temperature calibration formula model; obtaining the wavelength λ and doping concentration n of the sample; A and temperature T 0 , multiple measurements of T 0 The electron escape probability P under the condition 0 , fit the sample parameters according to the data; substitute the sample parameters and the target electron escape probability P into the formula model to calculate the output temperature T 1 ; Measure T 1 The electron escape probability P under the condition 1 , and judge P 1 The deviation s 1 Is it less than the set value? If it is less than the set value, the output temperature T=T 1 , if it is not less than the set value, then at T 1 Under the conditions of P 1 Fit the sample parameters again; calculate the output temperature T again based on the new sample parameters and P 2 ; Measure T 2 The electron escape probability P under the condition 2 And compare the deviation s 2 and set value; repeat the above steps until the deviation s n If it is less than the set value, the cycle ends and the optimal temperature T corresponding to P is output. n The present invention can realize real-time and precise control of the electron escape probability of the NEAGaN photocathode through the method of self-calibration of temperature, which has the advantages of improving its quantum efficiency, stability and other performance parameters and enhancing the working performance of the NEAGaN photocathode.

Description

Technical Field

[0001] The invention relates to the measurement and regulation of GaN photocathode electron escape probability parameters, and in particular to a method for real-time control of GaN photocathode electron escape probability. Technical Background

[0002] GaN is an extremely stable compound with high hardness, high melting point, high ionization degree, large band width, high breakdown electric field strength, high saturated electron drift velocity, large thermal conductivity, small dielectric constant, strong radiation resistance and good chemical stability. The third-generation semiconductor material GaN photocathode based on negative electron affinity (NEA) has the advantages of high quantum efficiency, small dark emission, good stability, and concentrated distribution of emitted electron energy, making it an ideal electron source material.

[0003] Based on the current technology, when the doping concentration of the NEAGaN photocathode sample and the wavelength of the incident light are determined, the quantum efficiency of the material can be basically determined. If the experimental results do not meet the requirements and the quantum efficiency needs to be adjusted, the raw materials need to be replaced and the experiment needs to be reactivated. In this experimental process, the quantum efficiency cannot be controlled online in real time, which will undoubtedly greatly increase the experimental cost and lead to very low experimental efficiency.

[0004] Studies have shown that the electron escape probability of NEAGaN photocathode can affect the quantum efficiency and is an important parameter for measuring the characteristics of GaN photocathode. In practical applications, the electron source is often required to achieve a specific quantum efficiency or maintain a specific quantum efficiency to improve the stability of the photocathode material, and the above purpose can be achieved by adjusting the size of the electron escape probability, so the measurement and regulation of the electron escape probability of NEAGaN photocathode is extremely important. Summary of the invention

[0005] The purpose of the present invention is to provide a method for real-time control of the NEAGaN photocathode electron source escape probability, and to achieve real-time and accurate control of the NEAGaN photocathode electron escape probability by a self-calibration temperature method. The method proposed by the present invention is significantly more advanced than the prior art.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The method for real-time control of the electron escape probability of the NEA GaN photocathode provided by the present invention first establishes a temperature calibration formula model for the electron escape probability of the NEA GaN photocathode, and the formula model is as follows:

[0008]

[0009] Where C is the normalization constant, which is determined by the following normalization formula:

[0010]

[0011] Where E is the thermalized electron energy, here E = 3.4 eV; is the difference between the thermalized electron energy and the bottom energy level of the conduction band; E0, α, and β are all GaN bandgap widths E g Correlation constants, E0 = 3.4789 eV, α = -9.39 × 10 -4 eV / K, β=772K; ε0 is the dielectric constant of vacuum, ε0=8.854×10 -12 F / m; ε is the relative dielectric constant of GaN, ε = 8.9; n A is the doping concentration of GaN in cm -3 ; e is the charge of an electron, e = 1.6 × 10 -19 C; L p is the electron scattering mean free path, L p =30nm; ΔE p is the average energy lost by the electron in each collision scattering, where ΔE p =35meV; k is the Boltzmann constant, k = 1.38×10 -23 J / K; m is the mass of the electron, m = 9.109 × 10 -31 kg; h is Planck's constant, h = 6.626 × 10 -34 J·s; The above mentioned parameters are not affected by temperature changes.

[0012] After the formula model is established, the following steps are performed:

[0013] (1) Determine the sample doping concentration n before the experiment begins A and the wavelength of the incident light, λ. After these two parameters are determined, they will remain unchanged in the following experiments. At the same time, the target electron escape probability P and the deviation setting value s are set.

[0014] (2) Obtain the temperature T0 under the initial experimental conditions, and measure the NEAGaN photocathode electron escape probability under T0 conditions multiple times as data samples, denoted as P 01 ,P 02 ,...,P 0m , and at the same time, the sample parameter δ is fitted according to the m sets of data obtained s0 ,V 20 ,V 30 ,b0;

[0015] (3) The sample is doped with a concentration of n A, the target electron escape probability P and the sample parameter calibration results are input into the formula model to calculate the output temperature T1;

[0016] (4) Measurement of the electron escape probability P of the NEAGaN photocathode under T1 conditions 11 ,P 12 ,...,P 1m , obtain m groups of data and calculate the deviation s1 of P1;

[0017] (5) Determine whether the deviation s1 is less than the deviation setting value s. If s1 is less than s, the output temperature T = T1. If s1 is not less than s, the sample parameter δ is fitted again according to the m sets of data obtained in step (4) under the condition of T1. s1 ,V 21 ,V 31 ,b1;

[0018] (6) Calculate the output temperature T2 based on the new sample parameter calibration result and the target electron escape probability P;

[0019] (7) Measurement of the electron escape probability P of the NEAGaN photocathode under T2 conditions 21 ,P 22 ,...,P 2m , and continue to compare the size relationship between the deviation s2 of P2 and the deviation setting value s;

[0020] (8) Repeat the above process of “measurement – ​​calculation – judgment” until P n Deviation from P s n If the deviation is less than the set value s, the cycle ends and the optimal temperature T corresponding to P is output. n .

[0021] Furthermore, the working incident light wavelength λ is a working wavelength value set by the system, and the value is generally in the range of 100 nm to 350 nm.

[0022] Furthermore, the target electron escape probability P is a value that needs to be achieved in actual work. Based on the existing data, the value of P is in the range of 0 to 0.8;

[0023] Furthermore, the deviation setting value s is set according to the accuracy required in practice, and generally the value of s is in the range of 0 to 0.1%;

[0024] Furthermore, the m groups of data are samples of the electron escape probability measured under certain temperature conditions. Since there are 4 temperature-related sample parameters in the formula model constructed in the present invention, the sample size should be at least 100 groups.

[0025] Furthermore, the method for measuring the electron escape probability of the NEA GaN photocathode under certain temperature conditions mentioned in steps (2), (4) and (7) is to quickly test the spectral response curve of the NEA GaN photocathode with a spectral response tester, and fit the height and slope of the obtained experimental curve with the theoretical curve of quantum yield, so as to calculate the electron escape probability of the NEA GaN photocathode.

[0026] Furthermore, the fitting process in step (2) and step (5) is as follows: using m sets of measurement data (P n ,T n ) and the formula model to fit the sample parameter δ s ,V2,V3,b calibration results, the sample parameters are band bending amount δ s , the end heights of surface I and II barriers V2 and V3, and the width of surface I barrier b.

[0027] Furthermore, the deviation s in step (4), step (7) and step (8) is n The calculation model is:

[0028]

[0029] Where n is the data sequence number, P n represents m groups of electron escape probability samples obtained, m is the number of samples of the electron escape probability, and P is the target electron escape probability.

[0030] Furthermore, the data generated in the above experimental steps can be used as reference values ​​for initial setting in the next experiment.

[0031] Furthermore, the method can accurately control the electron escape probability of the working NEA GaN photocathode in real time online.

[0032] Furthermore, the above measurement and calibration processes are all automatically performed by computer software and hardware. Only the target electron escape probability P, the deviation setting value s and the number of measurement samples m need to be input, and the experiment can finally output the optimal temperature T = T n and the actual deviation s n .

[0033] Advantages and beneficial effects of the present invention:

[0034] (1) Greatly meet the different requirements for the electron escape probability and quantum efficiency of NEA GaN photocathode in any experimental or application scenario.

[0035] (2) The real-time and precise control of the electron escape probability greatly improves the stability and durability of the NEA GaN photocathode material, and effectively enhances the working performance of the NEA GaN photocathode.

[0036] (3) The device is simple, easy to operate, has few disadvantages, and requires low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described in detail below in conjunction with specific embodiments, so as to provide a more in-depth interpretation of the technical features and advantages of the present invention. The specific embodiments of the present invention are only used to explain the present invention and should not be regarded as having any limiting effect on the protection scope of the present invention.

[0039] The method flow chart of the present invention is as follows Figure 1 As shown, there are many operating methods to implement this process, and this application only gives two specific embodiments as examples.

[0040] Embodiment 1

[0041] In this embodiment, the thickness is 200nm and the doping concentration is 3.0×10 -17 cm -3 , pure GaN material with Mg doping element, size of 10×10mm, and sapphire substrate.

[0042] After the temperature calibration formula model of the present invention is established, the following specific steps are included in this embodiment:

[0043] (1) Determine the sample doping concentration n before the experiment begins A 3.0×10 -17 cm -3 , the working incident light wavelength λ is 230nm. After these two parameters are determined, they will remain unchanged in the following experiments; the target electron escape probability P is set to 0.5, and the deviation setting value s is set to 0.04%;

[0044] (2) Obtain the temperature T0 under the initial experimental conditions, the measurement result is T0 = 300K, and measure the NEAGaN photocathode electron escape probability under the condition of temperature T0 = 300K as the data sample, and record 150 sets of data P 01 =0.3241,P 02 =0.3253,...,P 0150 =0.3327; fitting sample parameter δ based on 150 sets of data obtained s0 ,V 20 ,V 30 ,b0;

[0045] (3) The sample is doped with a concentration of n A =3.0×10 -17cm -3 , target electron escape probability P = 0.5 and sample parameter δ s0 ,V 20 ,V 30 ,b0 is input into the formula model, and the calculated output temperature T1=290K;

[0046] (4) Measure the electron escape probability of NEA GaN photocathode at temperature T1 = 290K as data samples, and record 150 sets of data P 11 =0.4025,P 12 =0.4074,...,P 1150 =0.3958;

[0047] (5) Calculate the deviation s1 of P1, the result is s1 = 1.8622%, judging that s1 is not less than s. Under the condition of temperature T1 = 290K, according to the 150 sets of data (P 11 =0.4025,P 12 =0.4074,...,P 1150 =0.3958), and fit the sample parameter δ again s1 ,V 21 ,V 31 ,b1;

[0048] (6) Combined with the new sample parameter δ s1 ,V 21 ,V 31 , b1 and the target electron escape probability P = 0.5 to calculate the output temperature T2, the result is T2 = 283K;

[0049] (7) Measure the electron escape probability at temperature T2 = 283K as data samples and record 150 sets of data P 21 =0.4692,P 22 =0.4737,...,P 2150 =0.4771, and continue to compare the deviation s2=0.1354% of P2 and the deviation setting value s;

[0050] (8) Repeat the above process of “measurement – ​​calculation – judgment” until the fifth calibration of δ s5 ,V 25 ,V 35 ,b5, combined with the existing data and formula model to calculate T6 = 271K, and measured 150 sets of data P under the temperature T6 = 271K 61 =0.4823,P 62 =0.4902,...,P 6150=0.4885, and the deviation between P6 and P is s6=0.0398%. It is judged that s6 is less than the deviation setting value s=0.04%, then the cycle ends and the optimal temperature T=271K corresponding to P is output.

[0051] Specifically, the deviation s in step (4), step (7) and step (8) is n The calculation model is:

[0052]

[0053] Where n is the data sequence number, P n Represents 150 sets of electron escape probability samples obtained.

[0054] Specifically, the data generated in the above experimental steps can be used as reference values ​​for initial setting in the next experiment.

[0055] Specifically, the method can accurately control the electron escape probability of the working NEA GaN photocathode in real time online.

[0056] Specifically, the above measurement and calibration processes are automatically performed by computer hardware and software. It is only necessary to input the target electron escape probability P=0.5, the deviation setting value s=0.04% and the number of samples m=150. The experiment finally outputs the optimal temperature T=271K and the actual deviation s6=0.0398%.

[0057] Embodiment 2

[0058] In this embodiment, the thickness is 200nm and the doping concentration is 1.6×10 -18 cm -3 , pure GaN material with Mg doping element, size of 10×10mm, and sapphire substrate.

[0059] After the temperature calibration formula model of the present invention is established, the following specific steps are included in this embodiment:

[0060] (1) Determine the sample doping concentration n before the experiment begins A 1.6×10 -18 cm -3 , the incident light wavelength λ is 300nm, and these two data will not change after the experiment begins; the target electron escape probability P is set to 0.6, and the deviation setting value s is 0.01%;

[0061] (2) Obtain the temperature T0 under the initial experimental conditions, the measurement result is T0 = 300K, and measure the NEAGaN photocathode electron escape probability under the condition of temperature T0 = 300K as the data sample, and record 200 sets of data P 01 =0.4358,P02 =0.4432,...,P 0200 =0.4329; Fitting sample parameter δ based on the 200 sets of data obtained s0 ,V 20 ,V 30 ,b0;

[0062] (3) The sample is doped with a concentration of n A =1.6×10 -18 cm -3 , target electron escape probability P = 0.6 and sample parameter δ s0 ,V 20 ,V 30 ,b0 is input into the formula model, and the calculated output temperature T1=286K;

[0063] (4) Measure the electron escape probability of NEA GaN photocathode at temperature T1 = 286K as data samples, and record 200 sets of data P 11 =0.5279,P 12 =0.5234,...,P 1200 =0.5318;

[0064] (5) Calculate the deviation s1 of P1, the result is s1 = 0.8425%, judging that s1 is not less than s, and according to the 200 sets of data (P 11 =0.5279,P 12 =0.5234,...,P 1200 =0.5318), and fit the sample parameter δ again s1 ,V 21 ,V 31 ,b1;

[0065] (6) Combined with the new sample parameter δ s1 ,V 21 ,V 31 , b1 and the target electron escape probability P = 0.6 to calculate the output temperature T2, the result is T2 = 277K;

[0066] (7) Measure the electron escape probability at temperature T2 = 277K as data sample and record 200 sets of data P 21 =0.5524,P 22 =0.5437,...,P 2200 =0.5516, and continue to compare the deviation s2=0.4167% of P2 with the deviation setting value s;

[0067] (8) Repeat the above process of “measurement – ​​calculation – judgment” until the seventh calibration of δs7 ,V 27 ,V 37 ,b7, combined with the existing data and formula model to calculate T8 = 268K, and measured 200 sets of data P under the temperature T8 = 268K 81 =0.5937,P 82 =0.5941,...,P 8200 =0.5895, and the deviation between P8 and P is s8=0.0098%. It is judged that s8 is less than the deviation setting value s=0.01%, then the cycle ends and the optimal temperature T=268K corresponding to P is output.

[0068] Specifically, the deviation s in step (4), step (7) and step (8) is n The calculation model is:

[0069]

[0070] Where n is the data sequence number, P n Represents 200 sets of electron escape probability samples obtained.

[0071] Specifically, the data generated in the above experimental steps can be used as reference values ​​for initial setting in the next experiment.

[0072] Specifically, the method can accurately control the electron escape probability of the working NEA GaN photocathode in real time online.

[0073] Specifically, the above measurement and calibration processes are automatically performed by computer hardware and software. It is only necessary to input the target electron escape probability P=0.6, the deviation setting value s=0.01% and the number of samples m=200. The experiment finally outputs the optimal temperature T=268K and the actual deviation s8=0.0098%.

[0074] Although specific embodiments of the present invention have been shown and described, the present invention is not limited to the above-described embodiments. It will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the spirit and circumstances of the present invention, and that these changes all fall within the scope of the present invention as claimed. The scope of the present invention as claimed is defined by the appended claims and their equivalents.

Claims

1. A method for real-time control of the electron escape probability of a NEA GaN photocathode, characterized in that: Establish a temperature calibration formula model for the electron escape probability of the NEA GaN photocathode, perform temperature self-calibration through multiple measurement and calculation steps, and achieve real-time control of the electron escape probability of the NEA GaN photocathode; The formula model is as follows: Where C is the normalization constant, which is determined by the following normalization formula: Where E is the thermalized electron energy, here E = 3.4 eV; is the difference between the thermalized electron energy and the bottom energy level of the conduction band; E0, α, and β are all GaN bandgap widths E g The relevant parameters are E0 = 3.4789 eV, α = -9.39 × 10 -4 eV / K, β=772K; ε0 is the dielectric constant of vacuum, ε0=8.854×10 -12 F / m; ε is the relative dielectric constant of GaN, ε = 8.9; n A is the doping concentration of GaN in cm -3 ; e is the charge of the electron, e = 1.6 × 10 -19 C; L p is the electron scattering mean free path, L p =30nm; ΔE p is the average energy lost by the electron in each collision scattering, where ΔE p =35meV; k is the Boltzmann constant, k = 1.38×10 -23 J / K; m is the mass of the electron, m = 9.109 × 10 -31 kg; h is Planck's constant, h = 6.626 × 10 -34 J·s; T is the sample temperature; δ s is the amount of band bending, V2 and V3 are the heights of the end of the surface I and II barriers, and b is the width of the surface I barrier; After the temperature calibration formula model is established, the following steps are performed based on the formula model: (1) Determine the sample doping concentration n A and the working incident light wavelength λ, set the target electron escape probability P and the deviation setting value s; (2) obtaining the temperature T0, measuring the electron escape probability P0 under the condition of T0 for multiple times, and fitting the sample parameters according to the m sets of data obtained; (3) The sample is doped with a concentration of n A , the target electron escape probability P and sample parameters are input into the formula model to calculate the output temperature T1; (4) Measure the electron escape probability P1 under T1 condition multiple times, obtain m sets of data, and calculate the deviation s1 of P1; (5) Determine whether the deviation s1 is less than the deviation setting value s. If s1 is less than s, the output temperature T=T1. If s1 is not less than s, the sample parameters are fitted again according to the m sets of data obtained under the condition of T1. (6) Calculate the output temperature T2 based on the new sample parameters and the target electron escape probability P; (7) measuring the electron escape probability P2 under the condition T2 and continuing to compare the deviation s2 of P2 with the deviation setting value s; (8) Repeat the above steps (5) to (7) until P n Deviation from P s n If the deviation is less than the set value s, the cycle ends and the optimal temperature T corresponding to P is output. n； Among them, the method for measuring the electron escape probability under certain temperature conditions mentioned in step (2), step (4) and step (7) is: using a spectral response tester to quickly test the spectral response curve of the NEA GaN photocathode, and fitting the height and slope of the obtained experimental curve with the theoretical curve of quantum yield, so as to calculate the electron escape probability of the NEA GaN photocathode.

2. A method for real-time control of electron escape probability of NEA GaN photocathode as claimed in claim 1, characterized in that: The working incident light wavelength λ is the working wavelength value set by the system; the target electron escape probability P is the value required for actual work; the deviation setting value s is set according to the accuracy required in actual conditions; the m groups of data are samples of electron escape probability obtained under certain temperature conditions.

3. A method for real-time control of electron escape probability of NEA GaN photocathode as claimed in claim 1, characterized in that: The fitting process in step (2) and step (5) is as follows: using m sets of measurement data (P n ,T n ) and the formula model to fit the sample parameter δ s ,V2,V3,b calibration results, the sample parameters are band bending amount δ s , the end heights of surface I and II barriers V2 and V3, and the width of surface I barrier b.

4. A method for real-time control of electron escape probability of NEA GaN photocathode as claimed in claim 1, characterized in that: The deviation s in step (4), step (7) and step (8) n The calculation model is: Where n is the data sequence number, P n represents m groups of electron escape probability samples obtained, m is the number of samples of the electron escape probability, and P is the target electron escape probability.

5. A method for real-time control of electron escape probability of NEA GaN photocathode as claimed in claim 1, characterized in that: The data generated in the above experimental steps can be used as reference values ​​for initial settings in the next experiment.

6. A method for real-time control of electron escape probability of NEA GaN photocathode as claimed in claim 1, characterized in that: This method can accurately control the electron escape probability of the working NEA GaN photocathode in real time.

7. A method for real-time control of electron escape probability of NEA GaN photocathode as claimed in claim 1, characterized in that: The above measurement and calibration process is automatically performed by computer hardware and software. You only need to input the target electron escape probability P, the deviation setting value s and the number of measurement samples m. The experiment can finally output the optimal temperature T and the actual deviation s. n .

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