Picosecond transient photocurrents in amorphous silicon

Three different types of $a-\mathrm{S}\mathrm{i}$, prepared by rf glow discharge, chemical vapor deposition, and evaporation, were found to have the same initial mobility of 1 ${\mathrm{cm}}^2$/V s at room temperature and different carrier relaxation times ranging from 200 to 4 ps. The initial mobility of $a-\mathrm{S}\mathrm{i}$:$\mathrm{H}$ is thermally activated with a prefactor of 8 ${\mathrm{cm}}^2$/V s. These results give strong support to the existence of a mode of conduction in extended states which is an intrinsic property of $a-\mathrm{S}\mathrm{i}$.