Anomalous substrate and annealing temperature dependencies of heavily boron-doped hydrogenated amorphous silicon

The 1% boron-doped hydrogenated amorphous silicon (a-Si:H) has a sharp absorption edge, a low density of gap states, and a large optical gap of 1.82 eV when the substrate temperature is around 90 °C. The photoconductivity of these samples is nearly independent of substrate and annealing temperatures, while the conductivity activation energy decreases with increasing the substrate (or annealing) temperature. The difference between the conduction band edge and the Fermi level decreases up to 250 °C, and then nearly saturates with an increase of the substrate temperature. This result can be applied to fabricate the high open-circuit voltage a-Si:H n-i-p solar cells.