Changes of infrared absorption by light soaking and thermal quenching in a-Si-H.pdf

ELSEVIER Solar Energy Materials and Solar Cells 49 (1997) 13-18 Solar Energy Materials and Solar Cells Changes of infrared absorption by light soaking and thermal quenching in a-Si H Tamihiro Gotoh*, Shuichi Nonomura, Satoshi Hirata, Naotsugu Masui, Shoji Nitta Department of Electronic and Computer Engineering, Gifu University, 1-1 Yanagido, Gifu 501-11, Japan Abstract The light- and thermal-induced changes of Si-H bonds in undoped a-Si : H have been studied on the infrared absorption of Si-H stretching mode, using the infrared photothermal deflection spectroscopy and the photothermal bending spectroscopy. The results show that the IR absorption of Si-H bonds increases by light soaking of the high power ~ 500 mW/cm z. The change of IR absorption of Si-H bonds reoccurs by thermal annealing at 200°C. This change is related to the increase of the dangling bonds under light soaking. Furthermore, we observe the change of the elasticity modulus by light soaking, using the photothermal bending spectro- scopy. The structural change in a-Si : H is discussed based on these results. PACS. 78.30.L; 61.43.D Keywords: Hydrogenated amorphous silicon; Infrared absorption; Photothermal bending spectroscopy; Photoinduced structural change 1. Introduction The light-induced effect in hydrogenated amorphous silicon (a-Si : H) is the most important problem in electronic applications. Many basic studies of the material have been reported for over ten years such as conductivity [1], electron spin resonance [2], the photoluminescence intensity [3] and the solar cell efficiency [4]. Recently, it is reported that the structural change is induced by light soaking [5]. Relating to the structural change, investigations about light-induced changes of Si-H bonds in a-Si : H have been done by using IR spectrometer. Both the increase and decrease of * Corresponding author. 0927-0248/97/$17.00 ? 1997 Elsevier Science B.V. All rights reserved PII S 0 9 2 7 - 0 2 4 8 ( 9 7