Doping Efficiency of N-Type a-Si:H Doped with a Liquid Organic Source

Abstract

N-type amorphous silicon films were grown using a mixture of silane and tertiarybutylphosphine (TBP-C4H11P) vapor in a plasma enhanced chemical vapor deposition system. The concentration of TBP in silane was varied from 0 to 3% by volume. As expected, at low doping levels, the photoluminescence (PL) intensity associated with both the band-tail recombination (peak at 1.3 eV) and deep-defect recombination (peak at 0.8 eV) decreased as the impurity concentration increased, but for TBP concentrations > 0.1% the PL intensity increased again. For moderate doping levels the activation energy for conductivity leveled off at ∼ 0.2 eV. For concentrations of TBP > 0.1% the activation energy for dark conductivity increased. A shift in the optical gap was observed for the highest impurity concentrations due to the incorporation of carbon from the TBP. These results are interpreted as a pronounced decrease in the doping efficiency for heavily doped films (> 0.1%) perhaps influenced by the increased carbon concentration.