Evidence for potential fluctuations in compensated amorphous silicon.

Measurements of the electron and hole drift mobilities and the optical-absorption edge in compensated hydrogenated amorphous silicon are reported. The mobilities of both carriers decrease with increasing doping and converge to similar values for gas-phase doping levels greater than one part per thousand. The mobility and optical-absorption data are not consistent with disorder-induced band-tail broadening, but agree with the predictions of a model of long-range potential fluctuations originating from charged donor and acceptor states.