INVESTIGATION OF AMORPHOUS-SILICON COMPENSATED MATERIALS OVER A WIDE-RANGE OF DOPANT CONCENTRATIONS

In this paper we present an extensive study of amorphous silicon compe nsated materials, grown from a mixture of undiluted silane, hydrogen d iluted phosphine and hydrogen diluted diborane. Two different compensa tion regimes were found. At low gas dopant concentration each dopant a cts as a single dopant and compensation is achieved for the phosphine/ diborane ratio equal to the inverse of their doping efficiency. At hig h gas dopant concentration, interaction of the two dopant species tend s to equalize their doping efficiencies. A dark conductivity around 10 (-11) Omega(-1) cm(-1), photosensitivity ratio under AM 1.5 of 6 order s of magnitude and defect density ranging from 8.5 x 10(15) to 1.5 x 1 0(17) cm(-3) were obtained. A decrease of photoconductivity with decre asing defect density has surprisingly been found in the as-grown sampl es, whereas during light-soaking samples with the lowest defect densit y degrade the fastest. These results suggest that the nature and kinet ics of defects in compensated films are different from those of intrin sic materials. (C) 1997 Elsevier Science S.A.