Study of light-induced annealing effects in a-Si : H thin films

Light-induced metastability was examined in hydrogenated amorphous silicon thin films using a 500 W xenon lamp and a 10 mW HeCd laser. Positron beam a nnihilation spectroscopy (PAS) and fourier transform infrared spectroscopy (FTIR) were examined to investigate the effects of light on the structural properties of the films. The experimental results exhibited significant dec rease in the S-parameter of the PAS, indicating marked reduction in the def ect density of the films. The FTIR spectroscopy showed significant reductio n in the transmission coefficient of IR radiation at frequencies correspond ing to Si-H and Si-H-3 phonon modes, indicating that the observed annealing effects were due to light-induced formation of Si-PI and Si-H-3 bonds, A s econd thermal annealing process conducted after the light exposure experime nt resulted in a further substantial decrease in defect density for the sam ple exposed to HeCd laser. The experimental results are explained by a comp eting, light induced, dangling bond creation/annealing process, in which th e incoming photons caused the annealing of dangling bonds, particularly tho se at around the voids. However, in the bulk region, the photons caused bot h the breaking of weak Si-Si bonds as well as the annealing of dangling bon ds. (C) 2001 Elsevier Science Ltd. All rights reserved.