Abstract

Picosecond photoinduced absorption (PA) has frequently been utilized to determine carrier relaxation processes in semiconductors. These processes are expected to be particularly interesting in amorphous materials since the scattering, relaxation, and trapping times are expected to be less than 1 nsec. Despite numerous studies of PA, there is considerable uncertainty regarding the interpretation of the PA decays in hydrogenated amorphous silicon (a–Si:H). Early work interpreted the PA decays in terms of holes thermalizing in the valence band tails¹ while more recently, the PA decays have been attributed to trapping of minority carriers into deep traps on the basis of fits to a multiple trapping model.² Alternatively, transient grating decays, which for large grating spacings are equivalent to PA decays, were ascribed to carrier diffusion to and recombination at the sample boundary.³ Further complicating interpretation of the PA decays is the recent finding that pressure waves can also contribute significantly to the observed PA decay.⁴

© 1986 Optical Society of America