CN115019912A - A method for real-time control of electron escape probability from NEA GaN photocathode - Google Patents

Abstract

The invention provides a method for real-time control of electron escape probability of _{NEAGaN photocathode} , specifically: establishing a formula model for temperature calibration _; The electron escape probability P ₀ is obtained, and the sample parameters are fitted according to the data; the sample parameters and the target electron escape probability P are substituted into the formula model to calculate the output temperature T ₁ ; the electron escape probability P ₁ under the condition of T ₁ is measured, And judge whether the deviation s ₁ of P ₁ is 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, fit the sample parameters again according to P ₁ under the condition of T ₁ ; Calculate the output temperature T ₂ again with the new sample parameters and P; measure the electron escape probability P ₂ under the condition of T ₂ and compare the deviation s ₂ with the set value; repeat the above steps until the deviation s _n is less than the set value, loop At the end, the optimal temperature T=Tn corresponding to P _is output. The invention can realize real-time precise control of electron escape probability of NEAGaN photocathode through the method of self-calibrating temperature, and has the advantages of improving its performance parameters such as quantum efficiency and stability, and improving the working performance of NEAGaN photocathode.

Description

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

technical field

The invention relates to the measurement and regulation of the electron escape probability parameter of a GaN photocathode, in particular to a method for real-time control of the electron escape probability of a NEAGaN photocathode.

technical background

GaN is an extremely stable compound with high hardness, high melting point, high ionization degree, large band width, high breakdown electric field strength, high saturation electron drift velocity, high thermal conductivity, low dielectric constant, It has the characteristics of 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, low dark emission, good stability, and concentrated energy distribution of emitted electrons, and is an ideal electron source material.

As far as the current technology is concerned, when the doping concentration of the NEAGaN photocathode sample and the wavelength of the working incident light are both determined, the quantum efficiency finally achieved by the material can also be basically determined. To regulate the efficiency, it is necessary to replace the raw materials and reactivate the experiment. In the process of this experiment, the quantum efficiency cannot be controlled online in real time, which will undoubtedly greatly increase the experimental cost and lead to low experimental efficiency.

Studies have shown that the electron escape probability of NEAGaN photocathode can affect the quantum efficiency, which is an important parameter to measure 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 probability of electron escape, so the NEAGaN photocathode electron escapes The determination and regulation of probability is extremely important.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a method capable of controlling the electron escape probability of NEAGaN photocathode in real time, and realize the real-time precise control of the electron escape probability of NEAGaN photocathode by means of self-calibrating temperature. Compared with the prior art, the method proposed by the present invention is obviously advanced.

In order to achieve the above object, the present invention adopts the following technical solutions:

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

where C is the normalization constant, determined by the following normalization formula:

是热化电子能量与导带底能级之差；E₀、α、β均为GaN禁带宽度E_g的相关常数，E₀＝3.4789eV，α＝ -9.39×10^-4eV/K，β＝772K；ε₀是真空介电常数，ε₀＝8.854×10^-12F/m；ε是GaN的相对介电常数，ε＝8.9；n_A是GaN的掺杂浓度，单位为cm^-3；e是电子的电荷量， e＝1.6×10^-19C；L_p是电子散射平均自由程，L_p＝30nm；ΔE_p是电子在每次碰撞散射中所损失的平均能量,此处取ΔE_p＝35meV；k是玻尔兹曼常数，k＝1.38×10^-23J/K；m是电子质量，m＝9.109×10^-31kg；h是普朗克常数，h＝6.626×10^-34J·s；以上提到的参数不受温度变化的影响。where E is the thermalized electron energy, where E=3.4 eV;

is the difference between the thermalized electron energy and the bottom energy level of the conduction band; E ₀ , α and β are the correlation constants of the forbidden band width E _g of GaN, E ₀ =3.4789eV, α = -9.39×10 ^-4 eV/K, β=772K; ε ₀ is the vacuum permittivity, ε ₀ =8.854×10 ^-12 F/m; ε is the relative permittivity of GaN, ε = 8.9; n _A is the doping concentration of GaN, in cm ^{- 3} ; e is the charge amount of the electron, e=1.6×10 ^-19 C; L _p is the mean free path of electron scattering, L _p =30nm; ΔE _p is the average energy lost by the electron in each collision scattering, here Take ΔE _p = 35meV; k is the Boltzmann constant, k = 1.38×10 ^-23 J/K; m is the electron mass, m = 9.109×10 ^-31 kg; h is Planck's constant, h = 6.626× 10 ^-34 J·s; the parameters mentioned above are not affected by temperature changes.

After the formula model is established, there are the following steps:

(1) Before the start of the experiment, determine the sample doping concentration n _A and the working incident light wavelength λ. After these two parameters are determined, they will be fixed in the next experiment; at the same time, set the target electron escape probability P and deviation setting value s;

(2) Obtain the temperature T ₀ under the initial experimental conditions, and measure the electron escape probability of the NEAGaN photocathode under the condition of T ₀ multiple times as a data sample, denoted as P ₀₁ , P ₀₂ ,..., P _0m , and at the same time according to the obtained m groups of data fitting sample parameters δ _s0 , V ₂₀ , V ₃₀ , b ₀ ;

(3) Input the sample doping concentration n _A , the target electron escape probability P and the sample parameter calibration results into the formula model, and calculate the output temperature T ₁ ;

( ₄ ) _Measure the electron _{escape probability} P ₁₁ , P ₁₂ , .

(5) Judging whether the deviation degree s ₁ is less than the set value s of the deviation degree, if s ₁ is less than s, the output temperature T ₌ T _{1 ;} The m groups of data are fitted again with the sample parameters δ _s1 , V ₂₁ , V ₃₁ , b ₁ ;

(6) Calculate the output temperature T ₂ in combination with the new sample parameter calibration result and the target electron escape probability P;

( ₇ ) _Measure the electron _{escape probability} P ₂₁ , P ₂₂ , .

(8) Repeat the above process of "measurement-calculation-judgment" until the degree of deviation s _n between P _n and P is less than the set value s of the degree of deviation, the cycle ends, and the optimal temperature T=T _n corresponding to P is output.

Further, the working incident light wavelength λ is the working wavelength value set by the system, and the value is generally in the range of 100 nm to 350 nm.

Further, the target electron escape probability P is a value that needs to be achieved in actual work, and in combination with existing data, the value of P is in the range of 0 to 0.8;

Further, the deviation degree setting value s is set according to the accuracy of the actual demand, and the value of s is generally in the range of 0 to 0.1%;

Further, the m groups of data are samples of the electron escape probability measured under a certain temperature condition. Since there are 4 temperature-related sample parameters in the formula model established by the present invention, the sample size should be at least 100 groups.

Further, the method for measuring the electron escape probability of NEA GaN photocathode under certain temperature conditions mentioned in step (2), step (4) and step (7) is to use a spectral response tester to quickly test the spectrum of NEA GaN photocathode. The response curve was fitted with the theoretical curve of quantum yield to the height and slope of the obtained experimental curve to calculate the electron escape probability of NEA GaN photocathode.

Further, the fitting process described in step (2) and step (5) is: using m groups of measurement data (P _n , T _n ) and the formula model fitting to obtain sample parameters δ _s , V ₂ , V ₃ , b calibration results, the sample parameters are the energy band bending amount δ _s , the terminal heights V ₂ and V ₃ of the surface I and II potential barriers, and the surface I potential barrier width b.

Further, the calculation model of the deviation degree s _n described in step (4), step (7) and step (8) is:

Wherein n is the data serial number, P _n represents the obtained m groups of electron escape probability samples, m is the sample number of the electron escape probability, and P is the target electron escape probability.

Further, the data generated in the above-mentioned experimental steps can be used as the initially set reference value in the next experiment.

Further, the method can precisely control the electron escape probability of the working NEA GaN photocathode in real time and online.

Further, the above measurement and calibration process are automatically carried out by computer software and hardware, only need to input the target electron escape probability P, the deviation setting value s and the number of measurement samples m, and the experiment can finally output the optimal temperature T= T _n and the actual degree of deviation s _n .

Advantages and beneficial effects of the present invention:

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

(2) The real-time precise control of the electron escape probability 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, the unfavorable factors are few, and the required cost is low.

Description of drawings

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

Detailed ways

The present invention will be further described in detail below with reference to specific embodiments, so as to further explain 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.

The flow chart of the method of the present invention is shown in FIG. 1 , and there are many operation methods for realizing the flow, and this application only exemplarily provides two specific embodiments.

Example 1

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

This embodiment has the following specific steps after the temperature calibration formula model of the present invention is established:

(1) Before the experiment, the doping concentration n _A of the sample was determined to be 3.0×10 ^-17 cm ^-3 , and the working incident light wavelength λ was 230 nm. After these two parameters were determined, they were fixed in the next experiment; set the target The electron escape probability P is 0.5, and the deviation setting value s is 0.04%;

(2) Obtain the temperature T ₀ under the initial experimental conditions, the measurement result is T ₀ =300K, and measure the electron escape probability of the NEAGaN photocathode under the condition of temperature T ₀ =300K as a data sample, and record 150 sets of data P ₀₁ =0.3241 , P ₀₂ =0.3253,...,P ₀₁₅₀ =0.3327; fit the sample parameters δ _s0 , V ₂₀ , V ₃₀ , b ₀ according to the 150 sets of data obtained;

(3) Input the sample doping concentration n _A = 3.0×10 ^-17 cm ^-3 , the target electron escape probability P = 0.5 and the sample parameters δ _s0 , V ₂₀ , V ₃₀ , b ₀ into the formula model to calculate the output temperature T ₁ =290K;

(4) Measure the electron escape probability of NEA GaN photocathode under the condition of temperature T ₁ =290K as a data sample, and record 150 sets of data P ₁₁ =0.4025, P ₁₂ =0.4074,...,P ₁₁₅₀ =0.3958;

(5) Calculate the deviation s ₁ of P ₁ , the calculation result is s ₁ =1.8622%, it is judged that s ₁ is not less than s, and under the condition of temperature T ₁ =290K, according to the 150 sets of data obtained in the previous step (P ₁₁ =0.4025, P ₁₂ =0.4074,...,P ₁₁₅₀ =0.3958), fit the sample parameters δ _s1 , V ₂₁ , V ₃₁ , b ₁ again;

(6) Calculate the output temperature T ₂ in combination with the new sample parameters δ _s1 , V ₂₁ , V ₃₁ , b ₁ and the target electron escape probability P=0.5, and the calculation result is T ₂ =283K;

(7) Measure the electron escape probability under the condition of temperature T ₂ =283K as a data sample, record 150 sets of data P ₂₁ =0.4692, P ₂₂ =0.4737,...,P ₂₁₅₀ =0.4771, and continue to compare the deviation of P ₂ The relationship between the degree s ₂ =0.1354% and the set value s of the deviation degree;

(8) Repeat the above process of “measurement-calculation-judgment”, after the fifth calibration δ _s5 , V ₂₅ , V ₃₅ , b ₅ , calculate T ₆ =271K in combination with the existing data and the formula model, and in Under the condition of temperature T ₆ =271K, 150 sets of data are measured, P ₆₁ =0.4823, P ₆₂ =0.4902,...,P ₆₁₅₀ =0.4885, and the degree of deviation between P ₆ and P s ₆ =0.0398% is obtained, and it is judged that s ₆ is less than Deviation degree setting value s=0.04%, the cycle ends, and the optimal temperature T=271K corresponding to P is output.

Specifically, the calculation model of the deviation degree s _n described in step (4), step (7) and step (8) is:

Among them, n is the data serial number, and P _n represents the obtained 150 sets of electron escape probability samples.

Specifically, the data generated in the above-mentioned experimental steps can be used as the initial set reference value in the next experiment.

Specifically, the method can precisely control the electron escape probability of the working NEA GaN photocathode in real time and online.

Specifically, the above measurement and calibration processes are automatically carried out by computer software and hardware, and 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 obtained m=150, and the final experiment The output optimum temperature T=271K and the actual deviation s ₆ =0.0398%.

Embodiment 2

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

This embodiment has the following specific steps after the temperature calibration formula model of the present invention is established:

(1) Before the experiment starts, the doping concentration n _A of the sample is determined to be 1.6×10 ^-18 cm ^-3 , and the working incident light wavelength λ is 300 nm. These two data will not change after the experiment begins; set the target electron The escape probability P is 0.6, and the deviation setting value s is 0.01%;

(2) Obtain the temperature T ₀ under the initial experimental conditions, the measurement result is T ₀ =300K, and measure the electron escape probability of the NEAGaN photocathode under the condition of temperature T ₀ =300K as a data sample, and record 200 sets of data P ₀₁ =0.4358 , P ₀₂ =0.4432,...,P ₀₂₀₀ =0.4329; fit the sample parameters δ _s0 , V ₂₀ , V ₃₀ , b ₀ according to the 200 sets of data obtained;

(3) Input the sample doping concentration n _A = 1.6×10 ^-18 cm ^-3 , the target electron escape probability P = 0.6 and the sample parameters δ _s0 , V ₂₀ , V ₃₀ , b ₀ into the formula model to calculate the output temperature T ₁ =286K;

(4) Measure the electron escape probability of NEA GaN photocathode under the condition of temperature T ₁ =286K as a data sample, and record 200 sets of data P ₁₁ =0.5279, P ₁₂ =0.5234,...,P ₁₂₀₀ =0.5318;

(5) Calculate the degree of deviation s ₁ of P ₁ , the calculation result is s ₁ =0.8425%, it is judged that s ₁ is not less than s, and under the condition of temperature T ₁ =286K, according to the 200 sets of data obtained in the previous step (P ₁₁ =0.5279, P ₁₂ =0.5234,...,P ₁₂₀₀ =0.5318), fit the sample parameters δ _s1 , V ₂₁ , V ₃₁ , b ₁ again;

(6) Calculate the output temperature T ₂ in combination with the new sample parameters δ _s1 , V ₂₁ , V ₃₁ , b ₁ and the target electron escape probability P=0.6, and the calculation result is T ₂ =277K;

(7) Measure the electron escape probability under the condition of temperature T ₂ =277K as a data sample, record 200 sets of data P ₂₁ =0.5524, P ₂₂ =0.5437,...,P ₂₂₀₀ =0.5516, and continue to compare the deviation of P ₂ The relationship between the degree s ₂ =0.4167% and the set value s of the deviation degree;

(8) Repeat the above process of "measurement-calculation-judgment", after the seventh calibration of δ _s7 , V ₂₇ , V ₃₇ , b ₇ , calculate T ₈ =268K based on the existing data and formula model, and in Under the condition of temperature T ₈ =268K, 200 sets of data are measured, P ₈₁ =0.5937, P ₈₂ =0.5941,...,P ₈₂₀₀ =0.5895, and the degree of deviation between P ₈ and P s ₈ =0.0098% is obtained, and it is judged that s ₈ is less than Deviation degree setting value s=0.01%, the cycle ends, and the optimal temperature T=268K corresponding to P is output.

Specifically, the calculation model of the deviation degree s _n described in step (4), step (7) and step (8) is:

Among them, n is the data serial number, and P _n represents the obtained 200 sets of electron escape probability samples.

Specifically, the data generated in the above-mentioned experimental steps can be used as the initial set reference value in the next experiment.

Specifically, the method can precisely control the electron escape probability of the working NEA GaN photocathode in real time and online.

Specifically, the above measurement and calibration processes are automatically carried out by computer software and hardware, and 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 obtained m=200, and the final experiment The output optimum temperature T=268K and the actual deviation s ₈ =0.0098%.

While specific embodiments of the present invention have been shown and described, the present invention is not limited by the foregoing embodiments. For those skilled in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the spirit and circumstances of the present invention, and these changes all fall within the scope of the claimed invention Inside. The claimed scope of the present invention is defined by the appended claims and their equivalents.

Claims (9)

1. A method for controlling electron escape probability of NEA GaN photocathode in real time is characterized in that a temperature calibration formula model about the electron escape probability of the NEA GaN photocathode is established, and the formula model is as follows:

where C is a normalization constant, determined by the normalization equation:

wherein E is thermalization electron energy, and E is taken as 3.4 eV;

is the difference between the thermalized electron energy and the conduction band bottom level; e ₀ And both alpha and beta are GaN forbidden band width E _g Related parameter of (E) ₀ ＝3.4789eV，α＝-9.39×10 ^-4 eV/K，β＝772K；ε ₀ Is the vacuum dielectric constant ε ₀ ＝8.854×10 ^-12 F/m; ε is the relative dielectric constant of GaN,. epsilon.8.9; n is _A Is the doping concentration of GaN in cm ^-3 (ii) a e is the charge amount of electrons, e is 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 collisional scatter, where Δ E is taken _p 35 meV; k is Boltzmann constant, k is 1.38 × 10 ^-23 J/K; m is electron mass, m is 9.109 × 10 ^-31 kg; h is Planck constant, h is 6.626 × 10 ^-34 J·s。

2. The method of claim 1, wherein the step of modeling the equation is performed by:

(1) determination of the doping concentration n of a sample _A And working incident light wavelength lambda, and setting a target electron escape probability P and a deviation set value s;

(2) obtaining a temperature T ₀ Measuring T a plurality of times ₀ Probability of electron escape under the conditions P ₀ Fitting sample parameters according to the obtained m groups of data;

(3) doping the sample with a concentration n _A Inputting the target electron escape probability P and the sample parameter into a formula model, and calculating the output temperature T ₁ ；

(4) Multiple measurement of T ₁ Electron escape probability under the condition of P ₁ Obtaining m sets of data and calculating P ₁ Degree of deviation s of ₁ ；

(5) Determining the degree of deviation s ₁ Whether is less than the deviation set value s, if s ₁ If less than s, the output temperature T is equal to T ₁ If s is ₁ Not less than s is 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 electron escape probability P ₂ ；

(7) Measurement of T ₂ Probability of electron escape under the conditions P ₂ And continue to compare P ₂ Degree of deviation s of ₂ And a deviation set value s;

(8) repeating the processes from the step (5) to the step (7) until P _n Degree of deviation s from P _n When the deviation degree is less than the set value s, the cycle is ended, and the optimal temperature T which corresponds to the P is output _n 。

3. The method of claim 2, wherein the wavelength λ of the incident light is a working wavelength set by a system; the target electron escape probability P is a value which needs to be reached by actual work; the deviation degree set value s is set according to the accuracy degree of the actual requirement; the m groups of data are obtained samples of electron escape probability under certain temperature conditions.

4. The method for real-time control of electron escape probability of NEA GaN photocathode according to claim 2, wherein the method for measuring electron escape probability under certain temperature condition mentioned in step (2), step (4) and step (7): the spectral response curve of the NEA GaN photocathode is quickly tested by a spectral response tester, and the height and the slope of the obtained experimental curve are fitted by using a theoretical curve of quantum yield, so that the electron escape probability of the NEA GaN photocathode is calculated.

5. The method of claim 2, wherein the fitting process in the steps (2) and (5) is as follows: using m sets of measurement data (P) _n ,T _n ) And fitting the formula model to obtain a sample parameter delta _s ,V ₂ ,V ₃ B, the calibration result of b, the sample parameter is respectively the energy band bending quantity delta _s Surface I and II barrier end height V ₂ And V ₃ Surface i barrier width b.

6. The method for real-time control of electron escape probability of NEA GaN photocathode according to claim 2, wherein the deviation s in step (4), step (7) and step (8) _n The calculation model of (a) is:

where n is the data sequence number, P _n And m groups of obtained electron escape probability samples are represented, m is the number of samples of the electron escape probability, and P is the target electron escape probability.

7. The method of claim 2, wherein the data generated in the experiment steps can be used as the reference value initially set in the next experiment.

8. The method of claim 2, wherein the method can precisely control the electron escape probability of the working NEA GaN photocathode in real time on-line.

9. The method of claim 2, wherein the measurement and calibration are performed automatically by computer hardware and software, only the target electron escape probability P, the deviation set value s and the measurement sample number m are input, and the experiment can output the optimal temperature T and the actual deviation s _n 。

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