Variation of Spectral Response Curve Shape of GaAs Photocathodes
ZOU Ji-jun1,2,CHANG Ben-kang1*,DU Xiao-qing1,YANG Zhi1
1. Institute of Electronic Engineering and Opto-electronic Technology, Nanjing University of Science and Technology, Nanjing 210094, China 2. Department of Electronic Engineering, East China Institute of Technology, Fuzhou 344000, China
Abstract：Using spectral response measuring instrument, the spectral response curves of reflection-mode GaAs photocathodes were obtained as a function of time during the process of activation and the process of illumination by white light after activation. The measured results show that the spectral response curve shape changes continuously during both processes. Due to the formation of double dipoles on the GaAs surface during the co-adsorption of cesium and oxygen, the surface electron affinity of photocathode decreases continuously, and spectral response increases continuously, but the spectral response of long wave increases faster. During the process of illumination by white light after activation, due to the double-dipole structure affected by the desorption of cesium, the surface electron affinity of photocathode increases continuously, and spectral response decreases continuously, but the spectral response of long wave decreases faster. Using traditional quantum efficiency formula of reflection-mode photocathodes, the above phenomena cannot be explained very well, and they have a relationship with the escape of high-energy electrons. Because the emitted electron energy-distribution of reflection-mode photocathodes shifts towards higher energies with the increase in photon energy, and the influence of the evolution of surface potential barrier profile on the low-energy electrons is greater, the spectral response curve shape changes during different processes.
Key words：GaAs photocathode;Spectral response curve;Electron energy distribution;Surface potential barrier;Electron escape probability
[1] Mulhollan G A, Subashiev A V, Clendenin J E, et al. Phys. Lett. A, 2001,282: 309. [2] Drouhin H J, Hermann C, Lampel G. Phys. Rev. B, 1985, 31(6) : 3859. [3] Liu Zhi, Machuca Francisco, Pianetta Piero, et al. Appl. Phys. Lett., 2004, 85(9): 1541. [4] James L W, Moll J L. Phys. Rev., 1969, 183(3): 740. [5] Gao Huai-rong. J. Vac. Sci. Technol. A, 1987, 5(4): 1295. [6] Moré S, Tanaka S, Tanaka S, et al. Surf. Sci., 2000, 454-456 (1-3): 161. [7] Spicer W E, Herrera-Gómez A. Proc. SPIE, 1993, 2022: 18. [8] Su C Y, Lindau I, Spicer W E. Chem. Phys. Lett., 1982, 87(6): 523. [9] Su C Y, Spicer W E, Lindau I. J. Appl. Phys., 1983, 54(3): 1413. [10] LU Yong-jun, CHEN Hua-cai, L Jin, et al(芦永军, 陈华才, 吕 进, 等). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2005, 25(8): 1243. [11] TANG Ai-wei, TENG Feng, GAO Yin-hao, et al(唐爱伟，滕 枫，高银浩，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析)，2006，26(12)： 2169. [12] LIN Peng, LIANG Chun-jun, DENG Zhen-bo, et al(林 鹏，梁春军，邓振波，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析)，2005, 25(1):23. [13] Chang Benkang, Du Xiaoqing, Liu Lei, et al. Proc. SPIE, 2003, 5209: 209. [14] ZONG Zhi-yuan, QIAN Yun-sheng, CHANG Ben-kang. Proc, SPIE, 2001,4580: 623. [15] QIAN Yun-sheng, ZONG Zhi-yuan, CHANG Ben-kang(钱芸生，宗志园，常本康). Vacuum Science and Technology(真空科学与技术)，2000，20(5)： 305.
