Picosecond photoconductivity measurements of mobility and lifetime in silicon-on-sapphire films

Abstract

Time-resolved photoconductivity and decay measurements in optoelectronic switches made from silicon-on-sapphire films of different thicknesses have been used to obtain the distributions of carrier drift mobility and lifetime as functions of the distance x from the substrate. It is shown that the evaluation of the true lifetime τ is complicated by the carrier diffusion in the case of thick samples (≫3 μm) and by back surface recombination in the case of thin samples (≤0.3 μm). For the lifetime, we have found the relation τ(ns)=0.4+0.4x (μm), and the rear surface recombination velocity has been determined to be of the magnitude s≂104 cm/s.