Conductivity and quenched-in defects in hydrogenated amorphous silicon

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Abstract
We report measurements of the electrical conductivity of hydrogenated amorphous silicon (a-Si:H) films prepared from laser-induced chemical-vapor deposition of silane. Intrinsic as well as p-type and n-type samples have been investigated, and the conductivity was measured after different annealing and quenching cycles. We suggest that metastable defects are introduced into the films via equilibration at high temperatures and are frozen in below a temperature that depends on thermal history. These defects result in a net movement of electronic states from below to above the Fermi level in phosphorus-doped a-Si:H and vice versa for boron-doped a-Si:H. We develop a model that is in agreement with the time dependence of the conductivity during annealing of these defects and determine that a 1.1-eV potential barrier retards equilibration.