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As a new kind of ultraviolet photocathode material, the negative-electron-affinity (NEA) GaN photocathode needs to further improve its photoemission performance and the stable performance in practical applications. Under the limit of GaN photocathode material growth level, how to further improve the quantum efficiency of cathode is an important problem. The varied doping technology can help to solve the problem under such circumstances. According to the photoemission mechanism of varying doping NEA GaN photocathode material, the built-in electric field formulas and the quantum efficiency formulas for reflection-mode varied doping NEA GaN photocathode are given. The preliminary structure of varied doping NEA GaN photocathode is designed. The varied doping material sample is divided into four layers according to the doping concentration. Using the self-developed experimental equipment, the varied doping GaN photocathode sample is activated with Cs/O. The activation process and the change characteristics of photocurrent for varied doping NEA GaN photocathode are discussed. At the beginning, the photocurrent is increased steady with the introduction of Cs, then the Cs kill phenomenon appears in the presence of excessive Cs. After the introduction of O, the photocurrent value starts to rise again. The spectral response of varied doping GaN photocathode is tested in situ after activation, and the quantum efficiency values ranging from 240 nm to 354 nm are obtained. On the basis of the obtained experimental results of quantum efficiency, combining to the typical quantum efficiency curve from University of California, the characteristics of quantum efficiency curves are analyzed. The results show that the quantum efficiency value for reflection-mode varied doping NEA GaN photocathode can reach 56% at 240 nm because of the built-in electric field, yet the quantum efficiency maximum value for uniform doping GaN photocathode is only 37% at 230 nm. The tested quantum efficiency maximum value of varied doping NEA GaN photocathode is improved much more than that of the uniform doping GaN photocathode. In a wider range of the incident light wavelength, the quantum efficiency of varied doping NEA GaN photocathode is relatively stable, and the excellent properties of varied doping GaN photocathode are confirmed. The reason why the value of quantum efficiency decreases with the increase of incident light wavelength is given. First, the photon energy decreases with the increase of incident light wavelength. Second, the incident light is absorbed from the front surface of cathode for reflection mode. In addition, the quantum efficiency curves of varied doping GaN photocathode show obvious sharp cut-off characteristics near the threshold, and the sharp cut-off characteristic is necessary for high detection sensitivity. The property of negative electron affinity for varied doping GaN cathode material after successful activation is also proved by the sharp cut-off feature.
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Keywords:
- GaN /
- photocathode /
- varied doping /
- quantum efficiency
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[2] Machuca F 2003 Ph. D. Dissertation (Stanford: Stanford University)
[3] Wang X H, Shi F, Guo H, Hu C L, Cheng H C, Chang B K, Ren L, Du Y J, Zhang J J 2012 Chin. Phys. B 21 087901
[4] Du X Q, Tian J, Zhou Q F 2011 Spectroscop. Spect. Anal. 31 1606 (in Chinese) [杜晓晴, 田健, 周强富 2011 光谱学与光谱分析 31 1606]
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[11] Hao G H, Chang B K, Chen X L, Wang X H, Zhao J, Xu Y, Jin M C 2013 Acta Phys. Sin. 62 097901 (in Chinese) [郝广辉, 常本康, 陈鑫龙, 王晓晖, 赵静, 徐源, 金睦淳 2013 物理学报 62 097901]
[12] Wang X H, Chang B K, Zhang Y J, Hou R L, Xiong Y J 2011 Spectroscop. Spect. Anal. 31 2655 (in Chinese) [王晓晖, 常本康, 张益军, 侯瑞丽, 熊雅娟 2011 光谱学与光谱分析 31 2655]
[13] Li B 2013 Ph. D. Dissertation (Nanjing: Nanjing University of Science and Technology) (in Chinese) [李飙 2013 博士学位论文(南京: 南京理工大学)]
[14] Wang X H 2013 Ph. D. Dissertation (Nanjing: Nanjing University of Science and Technology) (in Chinese) [王晓晖 2013 博士学位论文(南京: 南京理工大学)]
[15] Siegmund O H W, Tremsin A S, Vallerga J V, McPhate J B, Hull J S, Malloy J, Dabiran A M 2008 Proc. SPIE 7021 70211B
[16] Siegmund O, Vallerga J, McPhate J, Malloy J, Tremsin A, Martin A, Ulmer M, Wessels B 2006 Nucl. Instrum. Meth. Phys. Res. A 567 89
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[1] Yang Y F, Fu R G, Ma L, Wang X H, Zhang Y J 2012 Acta Phys. Sin. 61 128504 (in Chinese) [杨永富, 富容国, 马力, 王晓晖, 张益军 2012 物理学报 61 128504]
[2] Machuca F 2003 Ph. D. Dissertation (Stanford: Stanford University)
[3] Wang X H, Shi F, Guo H, Hu C L, Cheng H C, Chang B K, Ren L, Du Y J, Zhang J J 2012 Chin. Phys. B 21 087901
[4] Du X Q, Tian J, Zhou Q F 2011 Spectroscop. Spect. Anal. 31 1606 (in Chinese) [杜晓晴, 田健, 周强富 2011 光谱学与光谱分析 31 1606]
[5] Zhang Y J, Niu J, Zhao J, Xiong Y J, Ren L, Chang B K, Qian Y S 2011 Chin. Phys. B 20 118501
[6] Zhang Y J, Chang B K, Yang Z, Niu J, Zou J J 2009 Chin. Phys. B 18 4541
[7] Li B, Chang B K, Xu Y, Du X Q, Du Y J, Fu X Q, Wang X H, Zhang J J 2011 Spectroscop. Spect. Anal. 31 2036 (in Chinese) [李飙, 常本康, 徐源, 杜晓晴, 杜玉杰, 付小倩, 王晓晖, 张俊举 2011 光谱学与光谱分析 31 2036]
[8] Niu J, Qiao J L, Chang B K, Yang Z, Zhang Y J 2009 Spectroscop. Spect. Anal. 29 3007 (in Chinese) [牛军, 乔建良, 常本康, 杨智, 张益军 2009 光谱学与光谱分析 29 3007]
[9] Yang Z, Chang B, Zou J, Qiao J, Gao P, Zeng Y, Li H 2007 Appl. Opt. 46 7035
[10] Zou J J, Chang B K, Yang Z 2007 Acta Phys. Sin. 56 2992 (in Chinese) [邹继军, 常本康, 杨智 2007 物理学报 56 2992]
[11] Hao G H, Chang B K, Chen X L, Wang X H, Zhao J, Xu Y, Jin M C 2013 Acta Phys. Sin. 62 097901 (in Chinese) [郝广辉, 常本康, 陈鑫龙, 王晓晖, 赵静, 徐源, 金睦淳 2013 物理学报 62 097901]
[12] Wang X H, Chang B K, Zhang Y J, Hou R L, Xiong Y J 2011 Spectroscop. Spect. Anal. 31 2655 (in Chinese) [王晓晖, 常本康, 张益军, 侯瑞丽, 熊雅娟 2011 光谱学与光谱分析 31 2655]
[13] Li B 2013 Ph. D. Dissertation (Nanjing: Nanjing University of Science and Technology) (in Chinese) [李飙 2013 博士学位论文(南京: 南京理工大学)]
[14] Wang X H 2013 Ph. D. Dissertation (Nanjing: Nanjing University of Science and Technology) (in Chinese) [王晓晖 2013 博士学位论文(南京: 南京理工大学)]
[15] Siegmund O H W, Tremsin A S, Vallerga J V, McPhate J B, Hull J S, Malloy J, Dabiran A M 2008 Proc. SPIE 7021 70211B
[16] Siegmund O, Vallerga J, McPhate J, Malloy J, Tremsin A, Martin A, Ulmer M, Wessels B 2006 Nucl. Instrum. Meth. Phys. Res. A 567 89
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