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ABSTRACT: Based on the theoretical models of computing the photocathode optical performance, quantum yield and integral sensitivity, the photoemission characteristics of the domestic and ITT's transmission-mode extended blue GaAs photocathodes, namely the cathode optical properties and performance parameters, were respectively investigated. The compared results show that the integral sensitivity of the domestic transmission-mode extended blue photocathode has achieved 2,100 microA x lm(-1), still falling behind the ITT's integral sensitivity of 2,750 μA x m(-1). The reasons for the difference in quantum yield curves are that, on one hand, the thickness of GaAlAs window-layer and the Al mole fraction play a critical role in the short-wavelength response, especially in the extended blue region. On the other hand, the cathode performance parameters such as electron diffusion length and back interface recombination velocity work on the long-wavelength and short-wavelength response. All these factors are subject to the backwardness of basic industrial manufacturing level.
Guang pu xue yu guang pu fen xi = Guang pu 02/2012; 32(2):297-301. · 0.84 Impact Factor
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ABSTRACT: GaN photocathode has a wide applicaion in ultraviolet detection because of the outstanding performance. GaN photocathode was activated in ultrahigh vacuum (UHV) system by Cs/O, and the reflection-mode quantum efficiency (QE) was analyzed. The QE is 30%-10% corresponding to the wavelength 240-350 nm, and the QE curve is flat. The QE reaches the maximum of 30% at 240 nm. Compared with the abroad result, the QE obtained by us is still inadequate at the short wavelength The atom arrangement of GaN (0001) was studied. The atom arrangement on the surface was simulated by 3D, and in this way the adsorption of Cs on the GaN(0001) was speculated.
Guang pu xue yu guang pu fen xi = Guang pu 10/2011; 31(10):2655-8. · 0.84 Impact Factor
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ABSTRACT: Mechanism about the change of GaAs phtotocathode's surface barrier during Cs activated process was studied. Ionized Cs and p type doping impurity(Be) form a dipole that decreases the vacuum level of GaAs. Generally, Cs activated GaAs photocathode could achieve zero electron affinity state. The quantum yield formula of reflection-mode photocathode has been solved from the 1-dimension continuity equations and the escape probability formula has been solved from the Schrodinger equation. It was found from the formula that the quantum efficiency of Cs activated GaAs photocathode is directly proportional to the electric field intensity of Be- -Cs+ dipole. A Cs activation experiment was carried out, the experiment process tallies with the theory mentioned above and the integral sensitivity of Cs activated GaAs photocathode is 453 microA x lm(-1), which could be inferred as a zero electron affinity state.
Guang pu xue yu guang pu fen xi = Guang pu 08/2010; 30(8):2038-42. · 0.84 Impact Factor
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ABSTRACT: For a quantitative analysis of the effect of varied doping structure on the quantum efficiency of cathode, two kinds of reflective gradient doping GaAs photocathode samples were designed and grown respectively. After activation, the dynamic spectral response curves of the two samples were obtained. The spectral response curves were transformed into quantum efficiency curves. The quantum efficiency curves in different wavebands were fit, and the varied doping coefficient K that reflects the contribution of the varied doping structure to the cathode quantum efficiency was obtained. Results show that, the functional effects of the same material varied doping structure responding to the incident photon of different wavebands are different from each other. The same is true for the different material varied doping structures responding to the same waveband incident photon. The fundamental reasons for these differences are that the positions and the intensities of the inside electric fields which build within the materials under different varied doping structures are different from each other. It offers an effective analysis means to evaluate the structure performance of cathodes grown under different doping ways, and has great value for the study on optimization design of cathode varied doping structure.
Guang pu xue yu guang pu fen xi = Guang pu 11/2009; 29(11):3007-10. · 0.84 Impact Factor
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ABSTRACT: Appling the atomic structure theory to the research field of physical processes of lightning discharges, parameters such as wavelengths, oscillator strengths, transition probabilities and excitation energy of upper levels have been calculated for the transitions of N II ions related to lightning discharges. Large-scale multi-configuration Dirac-Fock wavefunctions were applied to include the most important effects of relativity, correlation, and rearrangement of the electron density within the same (computational) model. More detailed identification than ever for lightning spectra has been done, and reference data have been provided for further theoretic and experimental works on the physical mechanism of lightning discharges.
Guang pu xue yu guang pu fen xi = Guang pu 04/2004; 24(3):288-91. · 0.84 Impact Factor
