Abstract
Studies of the time evolution of the d.c. and a.c. photoresponse of hydrogenated amorphous silicon samples at low temperatures are reported. Both real and imaginary parts of the a.c. loss rise linearly with time to a steady state and then, on removal of the light, show a long-lasting signal due to trapped carriers. The initial rate of rise is proportional to illuminating intensity. The d.c. response is found to grow and decay much faster than that at finite frequencies. No sign of any transition from geminate to non-geminate regimes is seen. Current models are unable to explain the details of this behaviour.