Carrier collection efficiency of Schottky diodes on triode dc sputtered hydrogenated amorphous silicon: transport properties of holes

Spectral response of Schottky diodes has been used to determine the product μpτp (mobility-lifetime product of holes) of sputtered undoped and n-doped hydrogenated amorphous silicon. It is shown that the diffusion of holes in the space-charge region can be neglected in the calculation of the collection efficiency. Further, the influence of H content as well as dopant content on the transport properties of the holes has been investigated. Our results clearly demonstrate that (i) the incorporation of hydrogen leads to an increase of μpτp, and (ii) the n-type doping results in a drastic decrease of μpτp. Moreover, the behavior of the transport properties of the holes has been interpreted in the framework of the recombination model first proposed by Rose. For our samples, the variation of μpτp is controlled through the hole lifetime by the deep gap states which act as recombination centers. This interpretation has been confirmed by the influence of the photon flux intensity on the collection efficiency.