To enhance the spatial resolution capability of transmission-mode NEA GaAs photocathodes, this study employed a white-light interferometer to measure the surface configurations of photocathode components post thermal compression bonding. Precise fitting of the surface configurations was achieved using Zernike polynomials, successfully deriving the Zernike polynomial coefficients. Further, these calculated results were integrated into optical design software for modeling, aiming to elucidate the relationship between the photocathode's transfer function and surface configurations. The findings clearly indicate that the MTF value corresponding to 60lp/mm remains stable within the 0° and 5° field angles. However, as the field angle extends to 20°, there is a significant decline in the MTF value. Among them, the transfer performance of the plano-concave photocathode decreases most prominently, followed by the flat structure, while the plano-convex structure exhibits the least decline. Overall, this research provides invaluable references for the further advancement of photocathode technology.
As the photoelectric conversion material, semiconductor photocathode plays an important role in the development of vacuum photodetectors and electron sources, and the efficiency and stability of electron emission have always been the focus in photocathode applications. Photocathode is based on the external photoelectric effect. Different from the internal photoelectric effect, photoelectrons generated by light excitation inside the cathode must overcome the surface barrier to escape into the vacuum, so the level of the photoemission ability is closely related to the surface properties. The preparation process usually includes surface cleaning and activation, wherein the activation process under the ultrahigh vacuum condition is regarded as an irreversible and evolutionary process over time. How to characterize the cathode surface in situ is particularly important for understanding the mechanism of photoemission generation and degradation. Nowadays, the surface characterization methods including photoelectron spectroscopy, synchrotron x-ray characterization, electron diffraction, scanning probe microscopy, spectral response measurement, and photoreflectance spectroscopy are utilized as assisted evaluation tools to prepare photocathodes. Here, we present a newly developed integrated ultrahigh vacuum facility for photocathode preparation and in-situ characterization. With this system, the surface cleaning, activation and degradation processes for semiconductor photocathodes were effectively characterized by photoelectron spectroscopy and spectral measurement. The integrated photocathode preparation and characterization system can realize in-situ multi-information characterization in ultra-high vacuum environment, and the element composition and chemical state analysis of the specified region can be realized by using X-ray secondary electron image and micro-area analysis function, which is helpful to optimize the preparation process of photocathodes.
Three kinds of transmission type GaAlN photocathode materials with GaAlN activation layer/GaAlN absorber layer/AlN buffer layer/Al2O3 substrate layer multi-layer structures with different Al compositions were designed and grown. The thickness of the GaAlN activation layer, the GaAlN absorber layer and the AlN buffers layer of the three samples were 40 nm, 20 nm and 100 nm respectively. The Al fraction of the GaAlN activation layer of the three samples were 0.48, 0.37 and 0.25 respectively, and the Al fraction of GaAlN absorber layer were 0.8, 0.68 and 0.3 respectively. An ultraviolet waveband surface photovoltage testing device was developed for the measurement of the characteristics of surface photovoltage of the three GaAlN photocathode materials. The surface photovoltage amplitude curves of the three samples were basically the same under the two cases of frontal and reverse incidence, and the surface photovoltage signals obtained by the two different light incidence methods were differentiated, and the extreme points of the differentiation curves were obtained near the positions of 4.47 eV, 4.21 eV and 3.92 eV respectively, which correspond to the forbidden band width of the GaAlN material in the activation layer of the three samples. Comparing the surface photovoltage curves before activation with the spectral response curves after activation of two samples, it is found that the surface photovoltage curves before activation and the spectral response curves after activation are highly consistent in characteristics of spectral response and cut-off, which proves the effectiveness of surface photovoltage in the evaluation of characteristics of the spectral response of the GaAlN photocathode materials with multi-layer structures.
The underwater photoelectric detection equipment mainly uses 532 nm laser as the light source, and GaAlAs with Al component of 0.63 can obtain the cutoff wavelength near 532 nm, which is an excellent photocathode material to meet the requirement of narrow band spectral response of 532 nm laser. Furthermore, the light absorptance of the cathode can be improved effectively by the quadrangular prism or cylinder nanostructured arrays prepared on the reflection-mode Ga0.37Al0.63As cathode surface, and the maximum light absorptance can reach 96.2% at 532 nm, when the cylinder nanostructured array with a height of 900 nm and a base width of 100 nm. Nevertheless, the Ga0.37Al0.63As cathode with the quadrangular prism nanostructured array is less influenced by the incident angle of light.
Underwater photoelectric detection equipment with 532 nm laser as light source needs to match specific photocathodes to achieve the purpose of high quantum efficiency and narrow-band response. NEA GaAlAs photocathodes have a series of advantages, such as high quantum efficiency, adjustable spectral response cutoff threshold and long lifetime to serve as the devices for underwater detection. However, the quantum efficiency of GaAlAs photocathodes is not high enough to meet the actual detection requirements. In addition, micro-nano structures on the surface of materials have been proved to be an effective method to improve optical absorption. In this paper, four kinds of nanostructures including square column, cylinder, square cone and cone are designed. By the finite difference time domain method, results show that the optical absorptivity of reflection-mode GaAlAs photocathodes can be effectively improved. The optical absorptivity of square cone nanostructures increases and tends to be stable with the increase of filling factor. The optical absorptivity is approximately 100% at blue-green light region including 532 nm, and has an abrupt cutoff feature. Otherwise, when the absorptivity of square cone nanostructures is high and stable, the most intense light absorption part will move to the top of nanostructures with the increase of filling factor, thus effectively shortening the electron transport distance and improving the photoemission capability.
Semiconductor photocathodes with gradient-doping structures have attracted lots of interest in recent years because of their improved performances, such as higher quantum efficiency and longer diffusion length, over uniform-doped devices. It has been suggested that such improvement is due to the built-in electric field generated by the gradient of the doping concentration in the active layer. Under this built-in field, photoelectrons migrate toward the device surface via both diffusion and directional drift. While some past reports have studied and compared the photoelectron behaviors in uniform- and gradient-doped GaAs photocathodes, most of them are based on steady-state measurement and analysis. There has been little prior work focusing on dynamic responses. In this presentation, we report a comparative study of the ultrafast response of a uniform-doped and a gradient-doped GaAs photocathode, both theoretically and experimentally. We first develop a generalized diffusion-drift model, which adds a built-in electric field to a carrier diffusion model to incorporate the carrier drift. Then the theoretical model is used to predict the ultrafast transient behaviors of photoelectrons in both uniform- and gradient-doped photocathodes. Finally, the transient reflectivity of the photocathode devices is experimentally measured using pump-probe reflectometry (PPR), and the results are compared to the theoretical predictions. These comparisons indicate that the theoretical model is able to offer an appropriate physical picture of carrier transportation inside GaAs photocathodes of different doping profiles. It also enables the evaluation of device parameters such as diffusion coefficient and carrier decay time via PPR measurement.
In order to research H+ beam radiation on photoelectric performance of GaAs photocathodes used in low-light-level optoelectronic devices, based on Monte-Carlo method, quick calculation of damage, along with effects of Cs and Cs-O activation layer on ion trajectory, performance, ionization of ions and recoils are discussed. From the simulation results, the average stopping range increases with the increase of incident energy, and the dispersion varies with the incident angle, the minimum dispersion at 1 keV is obtained at 60° when Cs-O ratio is 2:1, and the minimum dispersion at 2 keV is obtained at 60° when Cs-O ratio is also 2:1. In addition, the produced vacancies increase with the incident energy while the value is almost not influenced by the incident angle, and the backscattered ions increase as the incident angle increase both in 1 keV and 2 keV cases, and decrease with the incident energy. Also, ionization dominate the H+ ion bombarding process instead of producing vacancies and phonons. With the increase of incident energy, the percentage of ionization of ions increases, while those of phonons of ions and ionization of recoils decrease. However, the corresponding percentages of ions and recoils remain nearly unchanged with the increase of incident angle and the variation of composition of Cs or Cs-O activation layer.
The desorption of oxygen and carbon contamination are a key issue on improving the quantum efficiency of negative electron affinity GaAs-based photocathode during the preparation process. In this article, O-bonded and C-bonded absorption are executed in the calculation of pristine (100)-oriented GaAs photocathode of planar structure and nanowire structure. By analyzing the absorption energy, work function and dipole moments of different adsorption models, it is found that the adsorption of impurity atoms changed atomic and electronic structure of GaAs(100) pristine surface and affected the stability. The findings suggest that, oxygen impurities are more difficult to remove than carbon impurities due to more negative absorption energies especially in the surface layer. However, C-absorbed models may have bigger work function values than O-absorbed models in the most cases, which are not beneficial to the photoemission, and the phenomenon can be verified by the calculation results of surface dipole moments.
Negative-electron-affinity GaAs-based photocathodes have already found widespread application in modern night vision detectors and vacuum electron sources. Considering the importance of surface micro-area analysis for cathode preparation, a new ultrahigh vacuum interconnection system for photocathode preparation and characterization was developed, wherein the scanning focused X-ray imaging positioning technique combined with the X-ray induced secondary electron image was applied to characterize the surface components in the specified micro region of semiconductor photocathodes. With the aid of the advanced characterization technique, the surface components of micro regions of interest for GaAs cathode samples after cleaning and Cs-O activation were analyzed. The experimental results show that the GaAs cathode samples would be subjected to secondary contamination from the metal sheet of sample holder, accompanied by a small amount of sodium and cesium. The subsequent heat treatment and Cs-O activation can hardly remove the sodium contamination, which can affect the arsenic desorption during heat treatment, hinder the Cs-O adsorption in the activation process, and finally reduce the photoemission performance of the activated cathode. Through the application of the X-ray induced secondary electron image, the optimal cleaning method for GaAs cathode was investigated. This surface characterization technique is of practical value to improving analysis accuracy and optimizing the cathode preparation process.
Negative electron affinity (NEA) GaAs photocathodes have attracted a wide scope of interest because of their high quantum efficiency and low dark emission. Traditionally, fabrication of GaAs photocathodes has taken two approaches: molecular beam epitaxy (MBE) and metal–organic chemical vapor deposition (MOCVD). Understanding the difference between these two methods in terms of device performance can help guide future device development. While past research has indicated that photocathodes grown by MOCVD generally have better spectral response and quantum efficiency, these reports are all based on steady-state analysis and measurement. There has been little prior work comparing the dynamic response of devices fabricated with different technologies. In this presentation, we report a comparative study of the ultrafast response of two gradient-doped GaAs photocathodes fabricated using two different methods, viz. MBE and MOCVD. Our approach is based on femtosecond pump-probe reflectometry (PPR), which measures the transient reflectivity of these devices upon optical excitation by femtosecond pulses. Preliminary PPR result shows that carrier build-up near photocathode surface in the MOCVD device is more efficient compared to the MBE device. A carrier-diffusion model is used to analyze photoelectron transport, accumulation, and decay in the active layer. Experiment-theory comparisons indicate a bi-exponential nature of free-electron population decay near device surface. Excellent agreement between theoretical predictions and measured data not only validates the numerical model but also allows various device parameters to be evaluated quantitatively.
A method that combines scanning white-light interferometry with phase-shifting interferometry is proposed. The best-focus scanning position of correlograms is located by calculating the maximum modulation contrast, and the twice averaging four-frame algorithm is utilized to determine the phase difference between the best-focus position and the zero optical path difference point. The surface height is obtained according to the best-focus frame position and the unwrapped phase, which is achieved by a process of removing the phase ambiguity. Both simulated and experimental results demonstrate that the advanced method can achieve the advantages of high precision, large dynamic range, and be insensitive to the phase shifting deviation.
To achieve negative-electron-affinity state, the atomically clean surface of GaAs-based photocathode is usually activated by cesium and oxygen in the ultrahigh vacuum environment. In view of the required computer-control of evaporation flow rates, the solid oxygen dispenser instead of gaseous oxygen is urgently needed just as the regular cesium dispenser. Accordingly, the solid cesium and oxygen dispensers were applied to activate epitaxial GaAs cathode samples. Two types of solid oxygen dispensers composed of barium peroxide powder and silver oxide powder respectively are employed to improve cathode photoemission performance. The experimental results show that the barium peroxidebased oxygen dispenser can release more oxygen and bring in higher activation photocurrent and spectral response than the silver oxide-based one. The unsatisfactory feature is that the silver oxide-based oxygen dispenser released effectual oxygen gas more slowly than the barium peroxide-based oxygen dispenser. Therefore, an effective activation technique was proposed to ameliorate this unfavorable phenomenon for the silver oxide-based dispenser, which can bring out the desired symmetry of photocurrent curve shape during the Cs/O alternate activation process. The improved activation technique would provide guidance for the optimization of activation craft.
Ultraviolet detection technology, as immediate area of research focus, has been adopted in the fields of fingerprint identification, corona detection and exhaust plume detection. Low-light CMOS, which can work in even 10-3lux, is used in visible light channel. The prominent advantage of the dual-channel Ultraviolet/Low-light CMOS camera is the fusion of UV and wide dynamic range visible light information, which can enrich image details and help observers locate the UV targets in the complicated background around the clock rapidly. The paper studied on the component structure of UV ICMOS, imaging driving, the Ultraviolet/Low-light images fusion algorithm and the photon counting algorithm. The one-inch and wide dynamic range CMOS chip with the coupling optical fiber panel are coupled to the UV image intensifier. In consideration of the ultraviolet detection demand, the driving circuit of the CMOS chips is designed and the corresponding program based on Verilog language is written. After analysis and comparison of the characteristics of UV image and Low-light CMOS image, the improved Laplace pyramid fusion algorithm is applied. UV image and Low-light CMOS image are multiscale decompose, and the features in different frequency layer are chosen from either UV image or Low-light CMOS image. The connected components labeling way is utilized for the UV detection and imaging. At last, the detection experiments of the ultraviolet signal are carried out, and the results are given and analyzed.
To research the attenuation performance of the AlGaN photocathode, three samples with same structures grown by metalorganic chemical vapor deposition (MOCVD) were activated with three different activation methods, which are Cs-only, Cs-O and Cs-O-Cs activation, respectively. The spectral responses and attenuated photocurrents of three AlGaN photocathodes were measured, the result shows that the Cs-O activated AlGaN photocathode have the lowest attenuation speed in the first few hours, the next are Cs-O-Cs and Cs-only activation, respectively. After the Cs-O-Cs activation sample has attenuated 90 min, its attenuation photocurrent curve is coincident with the Cs-O activation sample in the next measurement. The main factor which affects the photocurrent attenuation is Cs atom desorbed from the photocathodes surface.
In view that enhancing near-infrared response of photocathodes is critical to the detection performance, we propose two technical approaches by changing the structure of buffer-layer underneath the active-layer, wherein one is to produce a graded band gap using the graded-composition structure, and the other is to produce a distributed Bragg reflector using the AlAs/GaAs supperlattice structure. Three types of reflection-mode GaAs photocathode samples grown by molecular beam epitaxy were prepared under the same condition. By comparison of activation photocurrent and spectral response among the three different samples, it is found that compared with the conventional sample, the samples with graded-composition and distributed Bragg reflector can obtain higher photocurrent and better response. The measured results of spectral response indicate that the samples without a distributed Bragg reflector exhibit a typical smooth spectral behavior, while the spectral response of the sample with a distributed Bragg reflector structure has a different resonance feature. The sample with the distributed Bragg reflector structure can obtain higher response than those without distributed Bragg reflector at some near-infrared wavelength positions. The peak positions of spectral response curve agree quite well with the dip positions in the reflectivity spectrum. This agreement demonstrates that the response enhancements are ascribed to the resonant absorption effect.
KEYWORDS: Microchannel plates, X-ray detectors, X-rays, Gold, Signal processing, Power supplies, Computing systems, Night vision, Control systems, Structural design
Microchannel Plates(MCP) have been widely used in X-ray detection, night vision and other fields. X-ray detection used
in the field of space usually requires a lot of large area of MCPs. A set of multi-station electron scrubbing and
performance testing device for large area MCP is developed in this paper. Four sets of large area electron source are
designed for electron scrubbing. Aiming at single MCP and dual-MCP structure, the high voltage power system, signal
processing module and mechanical control structure are designed to achieve scrubbing and testing of 4 groups of large
area MCP at the same time. By using this device, the scrubbing and testing of large area MCPs of 106mm in diameter are
achieved. The test results are given and analyzed.
The resolution model of graded doping and graded composition reflection-mode AlGaAs/GaAs photocathode is solved numerically from the two-dimensional continuity equations. According to the model, the theoretical modulation transfer functions (MTFs) of different structure reflection-mode photocathodes were calculated, and the effects of doping concentration, Al composition, AlGaAs and GaAs layer thickness on the resolution of cathodes were analyzed. The simulation results show that both graded composition and graded doping structures can increase the resolution of photocathode, and the effect of graded composition structure is more pronounced. The resolution improvement is attributed to the built-in electric field induced by a graded composition or doping structure. The simulation results also show that the MTFs of cathodes are affected by the AlGaAs and GaAs layer thickness.
The UV image intensifier is one kind of electric vacuum imaging device based on principle of photoelectronic imaging.
To achieve solar-blind detection, its spectral response characteristic is extremely desirable. A broad spectrum response
measurement system is developed. This instrument uses EQ-99 laser-driven light source to get broad spectrum in the
range of 200 nm to 1700 nm. A special preamplifier as well as a test software is work out. The spectral response of the
image intensifier can be tested in the range of 200~1700 nm. Using this spectrum response measuring instrument, the
UV image intensifiers are tested. The spectral response at the spectral range of 200 nm to 600 nm are obtained. Because
of the quantum efficiency of Te-Cs photocathode used in image intens ifier above 280nm wavelength still exists,
especially at 280 nm to 320nm.Therefore, high-performance UV filters is required for solar blind UV detection. Based on
two sets of UV filters, the influence of solar radiation on solar blind detection is calculated and analyzed.
There exist limitations of conventional quantum efficiency models for both reflection-mode (r-mode) and
transmission-mode (t-mode) exponential-doped GaAs photocathodes in some cases. The revised quantum efficiency
models of the r-mode and t-mode photocathodes are solved from the one-dimensional continuity equations, wherein the
built-in electric field in the GaAs layer and the electrons generated from the AlGaAs layer are considered. According to
the revised models, the effects of some relational performance parameters are analyzed, such as the thicknesses of GaAs
layer and AlGaAs layer, and the interface recombination velocity on the quantum efficiency for t-mode and r-mode
photocathodes in combination with the conventional models. The results show that the main contribution of
photoelectrons generated from AlGaAs layer to quantum efficiency in the shortwave (i.e. high incident photon energy)
region, depends on the factors including cathode thickness and interface recombination velocity.
Based on the studies of the GaAs photocathode, the surface model of the InGaAs photocathode is investigated and the
energy distributions of electrons reaching the band bending region, reaching the surface and emitting into vacuum are
calculated. We use the quantum efficiency formula to fit the experimental curves, and obtain the performance parameters
of the photocathode and the surface barrier parameters. The results show that the electron escape probability is seriously
influenced by energy distribution and plays an important role in the research of high quantum efficiency as well. After
the theoretical calculation, the energy range of electrons crossing the BBR broaden, the peak of the electron energy
distribution shifts forward to low energy, the number of low energy electrons increases obviously; The surface barriers of
the InGaAs photocathode is similar to that of the GaAs photocathode. The height of barrier II not only decreases the
number of electrons, but also makes the width of electron energy distribution narrow. The prepared transmission-mode
InGaAs photocathode contains 20% InAs and 80% GaAs. This combination of InGaAs photocathodes is widely used in
the weak light detection field, such as night vision technology, forest fire prevention and harsh climate monitoring.
With an attempt to improve the photoelectron emission efficiency, a gradient-doping structure proposed based on the
Spicer's three-step model has been applied to the preparation of the transmission-mode GaAs photocathode via
molecular beam epitaxy technique. The Cs-O activation phenomenon suggests that the gradient-doping structure can
bring a potential photoemission capability with the increase of activation time, and the spectral response curves show
that the gradient-doping photocathode can obtain a higher response capability in the entire waveband region, especially
in the regions of short-wavelength threshold and long-wavelength threshold. By fitting quantum yield curves, the
obtained cathode performance parameters such as electron average diffusion length and electron escape probability of the
gradient-doping photocathode are greater than those of the uniform-doping one. The electron average diffusion length of
the gradient-doping photocathode achieves 3.2 μm. The improvement in cathode performance of the gradient-doping photocathode could be ascribed to the downward gradient band-bending structure.
The built-in electric fields formed in varied doped GaAs photocathode may promote the transport of electrons from the
bulk to the surface, thus the quantum efficiency of varied doped cathode can be enhanced remarkably. But the really
reason of this enhancement, which may be either the increase in the amounts of electrons reaching the surface, or the
increase in the energy of the electrons arriving at the surface, is not clear at present. In this paper, the electrons energy
distributions in varied doped photocathode and uniformed doped photocathode before and after the electrons escape
from the cathode surface were analyzed, and the amounts of the electrons escaped from the surface in different case
were calculated for the two kinds of photocathode. The analysis results according to the experimental result indicate
that, the varied doping structure may not only increase the amounts of the photoelectrons arriving at the surface, but
also cause an offset of the electrons energy distribution to high energy, and which is the root reason for the
enhancement of the quantum efficiency.
To improve the performance of GaAs NEA photocathodes, an exponential-doping structure GaAs material has
been put forward, in which from the GaAs bulk-to-surface doping concentration is distributed gradiently from high to
low. We apply this exponential-doping GaAs structure to the transmission-mode GaAs photocathodes. This sample was
grown on the high quality p-type GaAs (100) substrate by MBE with p-type Be doping. We have calculated the
band-bending energy in exponential-doping GaAs emission-layer, and the total band-bending energy is 59 meV which
helps improve the photoexcited electrons movement towards surface for the thin epilayer. The integrated sensitivity of
the two exponential-doping GaAs photocathode samples with different thickness reaches 1228uA/lm and 1547uA/lm
respectively.
Negative electron affinity (NEA) Gallium Nitride (GaN) photocathode is an ideal new kind of UV photocathode. NEA
GaN photocathode is widely used in such fields as high-performance ultraviolet photoelectric detector, electron beam
lithography etc. The preparation of negative electron affinity gallium nitride photocathode relates to the growth
technology, the cleaning method, the activation method and the evaluation of photocathode. The mainstream growth
technology of GaN photocathode such as metal organic chemistry vapor phase deposits technology, molecule beam
epitaxial technology and halide vapor phase epitaxial technology were discussed. The chemical cleaning method and the
heat cleaning method for GaN photocathode were given in detail. After the chemical cleaning, the atom clean surface
was gotten by a 700 °C heat about 20 minutes in the vacuum system. The activation of GaN photocathode can be realized
with only Cs or with Cs/O alternately. Using the activation and evaluation system for NEA photocathode, the
photocurrent curve during Cs activation process for GaN photocathode was gotten. The evaluation of photocathode can
be done by measuring the quantum efficiency. Employing the UV spectral response measurement instrument, the
spectral response and quantum efficiency of NEA GaN photocathode were measured. The measured quantum efficiency
of reflection-mode NEA GaN photocathode reached up to 37% at 230 nm.
At present, two kinds of activation techniques for preparing GaAs NEA photocathode are available. In this paper,
according to two kinds of photocurrent curve arising in the activation, the characteristic and mechanism of the two kinds
of craft were summed up and compared with each other, and the further theoretical investigation on the mechanism of
activation was carried out based on the recent research of NEA surface model for GaAs photocathode. It is proposed as a
process principle that during (Cs, O) alternation phase of the activation process of GaAs photocathode, Cs should always
be in excessive state. Besides, it is also indicated that whether Cs is excessive during (Cs, O) alternation phase and the
Cs/O ratio may affect directly the final property of photocathode. Finally, a method to modify the craft parameters to
guard against the deviation from the principle is presented. The presented study is very necessary and significative for
optimizing the activation techniques so as to enhance the performances of GaAs NEA photocathodes.
The exponential-doping structure was applied to prepare the transmission-mode GaAs photocathode, and spectral
response curves after high-temperature activation, low-temperature activation and the indium sealing process were
respectively measured by use of the on-line spectral response measurement system, to research into the practical effect of
the exponential-doping structure on cathode performance. The results show that a high photosensitivity ranging from 560
nm to 880 nm with an ascending trend can be obtained after the high-low temperature activation. In the region of longwave
threshold, there is a distinct inflexion indicating a better photoemission capability than the former uniform-doping
photocathodes. Besides, the spectral response curve in the whole response waveband, especially the long-wave region
obviously decreases after indium seal. Compared with the fitted surface electron escape probability after Cs-O activation,
it decreases after indium seal according to the quantum efficiency formula of exponential-doping transmission-mode
GaAs photocathodes. Based on the double dipole model, the reasons for the variation of spectral response shape are
explained on account of the relation between surface escape probability and the evolution of surface potential barrier
profile.
Gallium Nitride (GaN) photocathodes are potentially attractive as UV detective materials and electron sources. Based on
the activation and evaluation system for GaAs photocathode, which consists of ultra-high vacuum (UHV) activation
chamber, multi-information measurement system, X-ray photoelectron spectroscopy (XPS), and ultraviolet ray photoelectron
spectroscopy (UPS), the control and measurement system for the activation of UV photocathodes was
developed. The developed system, which consists of Xenon lamp, monochromator with scanner, signal-processing
module, power control unit of Cs and O source, A/D adapter, digital I/O card, computer and software, can control the
activation of GaN photocathodes and measure on-line the spectral response curves of GaN photocathodes. GaN materials
on sapphire substrate were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) with p-type Mg doping. The
GaN materials were activated by Cs-O. The spectral response and quantum efficiency (QE) were measured and
calculated. The experiment results are discussed.
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