Steady-state photoconductivity in a-Si:H prepared by d.c. magnetron methods

The steady-state photoconductivity of amorphous silicon produced from glow discharge in a d.c. magnetron has been studied. Cylindrical and planar magnetrons were used. Measurements were made over a range of temperatures and illumination intensities. Recombination models involving traps, alone, and combined with deep-level defects, are analysed and applied to our data. The activation energy or conduction in the dark determines the activation energy for photoconduction. It also determines whether recombination involves only tail-state traps or whether deep-level defects play a part. Surface band bending, present in various degrees, controls the dark- and photoresponse. The exponent γ in the intensity dependence depends on temperature in the usual Rose model format. However, the characteristic temperature depends not just on the steepness of the tail states but on the positions of the dark and quasi-Fermi levels. Values of γ below 1/2 are then allowed. Many estimates of tail-state densities reported up until now are probably too steep as they have misinterpreted this characteristic temperature.