Comparison of the photoemission behaviour.pdfVIP

Chin. Phys. B Vol. 20, No. 4 (2011) 048501 Comparison of the photoemission behaviour between negative electron affinity GaAs and GaN photocathodes? Zhang Yi-Jun(张益军), Zou Ji-Jun(邹继军), Wang Xiao-Hui(王晓晖), Chang Ben-Kang(常本康)?, Qian Yun-Sheng(钱芸生), Zhang Jun-Ju(张俊举), and Gao Pin(高 频) Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing 210094, China (Received 26 October 2010; revised manuscript received 1 December 2010) In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoe- mission behaviour, namely the activation process and quantum yield decay, between the two typical types of III–V compound photocathodes have been investigated using a multi-information measurement system. The activation exper- iment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs–O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes. Keywords: III–V photocathode, negative electron affinity, Cs–O activation, quantum yield decay PACS: 85.60.Ha, 73.61.Ey, 73.20.At, 79.60.–i DOI: 10.1088/1674-1056/20/4/048501 1. Introduction III–V negative electron affinity (NEA) photo- cathodes have already found widespread applications in vacuum detecting devices and polarized electron sources because of their high quantum efficiency, low dark current emission and narrow energy spread qualities.[1?4] As the two main types of III–V com- pound semiconductors, GaAs and GaN photocathodes have attracted extensive attention due to their respec- tive use as low-light visible detectors and solar-b