Research on High Temperature Cs Activated GaAs Photocathode
Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing 210094, China.Guang pu xue yu guang pu fen xi = Guang pu (Impact Factor: 0.29). 08/2010; 30(8):2038-42. DOI: 10.3964/j.issn.1000-0593(2010)08-2038-05
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.
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ABSTRACT: By solving the one-dimensional diffusion equation for equilibrium minority carriers of transmission-mode GaAs phtotocathodes, the equations for surface photovoltage spectroscopy of exponential and uniform doping transmission-mode GaAs photocathodes are deduced. Through metal organic chemistry vaporation deposition (MOCVD) technique, two GaAs photocathodes of different doping structures with the same active layer depth are designed. By measuring and theoretically emulating the surface photovoltage spectroscopy curves for two materials, the exponential doping structure can well increase the electric diffusion length for transmission-mode GaAs photocathodes. The reason is that the internal electric field can drive the photo-excited electrons to move toward surface barriers through both diffusing and electric field drifting, thus can finally elevate the emission efficiency and the surface photovoltage spectroscopy. The difference of two surface photovoltage spectroscopy waves can be well explained by the internal energy band equations and electron scattering theory.Chinese Journal of Lasers 09/2011; 38(9):0906002. DOI:10.3788/CJL201138.0906002
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ABSTRACT: Two types of transmission-mode GaAs photocathodes grown by molecular beam epitaxy are compared in terms of activation process and spectral response, one has a gradient-doping structure and the other has a uniform-doping structure. The experimental results show that the gradient-doping photocathode can obtain a higher photoemission capability than the uniform-doping one. As a result of the downward graded band-bending structure, the cathode performance parameters, such as the electron average diffusion length and the surface electron escape probability obtained by fitting quantum yield curves, are greater for the gradient-doping photocathode. The electron diffusion length is within a range of from 2.0 to 5.4 μm for doping concentration varying from 1019 to 1018 cm−3 and the electron average diffusion length of the gradient-doping photocathode achieves 3.2 μm.Chinese Physics B 11/2011; 20(11). DOI:10.1088/1674-1056/20/11/118501 · 1.60 Impact Factor
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