Carrier Relaxation in a-Si:H/a-Sic:H Multilayers Studied by Picosecond Transient Reflectometry

The dynamics of photocarriers under high excitation in a series of a-Si: H/a-SiC: H multilayer structures with different bilayer thicknesses is studied with picosecond resolution using pump-and-probe reflectivity measurements. By varying both the photon energy and the intensity of the pump beam, the processes of carrier thermalization from extended into localized states on a picosecond time scale and free carrier trapping assisted processes on a nanosecond time scale are identified. The obtained relaxation time dependence on bilayer thickness is explained in terms of the competition of carrier scattering and enhanced recombination processes at the interfaces. The parallel and perpendicular transport peculiarities of photogenerated carriers are discussed.