SOME OBSERVATIONS ON THE PHOTOCONDUCTIVITY OF AMORPHOUS-SEMICONDUCTORS

The effect of doping on the steady-state photoconductivity, sigma(p), of hydrogenated amorphous silicon (a-Si:H) was explored down to temperatures of 4.2 K. Thermal quenching (TQ) is found in both n-type and p-type samples. The temperature of TQ decreases montonically as the Fermi level is moved downward through the gap center. Electrons are the photocarriers below TQ and holes above TQ in undoped and p-type a-Si:H. A determination of type of photocarriers for hopping photoconductivity below 40 K yields electrons for n-type and holes for strongly p-type a-Si:H. The localization radii of localized conduction band tail states, a approximately 13 angstrom, and of valence band tail states, a approximately 7 angstrom, were determined from the dependence of the photocurrent on temperature and high electric fields. The temperature dependence of sigma(p) of amorphous boron and boron carbon alloys is compared with those of other amorphous semiconductors.