Investigation of amorphous silicon compensated materials over a wide range of dopant concentrations

In this paper we present an extensive study of amorphous silicon compensated materials, grown from a mixture of undiluted silane, hydrogen diluted phosphine and hydrogen diluted diborane. Two different compensation regimes were found. At low gas dopant concentration each dopant acts as a single dopant and compensation is achieved for the phosphine/diborane ratio equal to the inverse of their doping efficiency. At high gas dopant concentration, interaction of the two dopant species tends to equalize their doping efficiencies. A dark conductivity around 10(-11) Omega(-1) cm(-1), photosensitivity ratio under AM 1.5 of 6 orders of magnitude and defect density ranging from 8.5 x 10(15) to 1.5 x 10(17) cm(-3) were obtained. A decrease of photoconductivity with decreasing defect density has surprisingly been found in the as-grown samples, whereas during light-soaking samples with the lowest defect density degrade the fastest. These results suggest that the nature and kinetics of defects in compensated films are different from those of intrinsic materials. (C) 1997 Elsevier Science S.A.