Electron and hole μτ products of slightly doped a-Ge:H films

Abstract

We measured the spectral photoconductance of slightly boron doped amorphous germanium (a-Ge:H) films through the wavelength interval from 450 to 950 nm, and determined the products ( μτ ) n of electrons and ( μτ ) p of holes by means of an own two-carrier photoconductance model. The doping was achieved by adding diborane (B 2 H 6 ) to the germane (GeH 4 ) gas in the deposition chamber, in concentrations up to 0.3%. In nominally undoped films the product ( μτ ) n exceeds the product ( μτ ) p by two orders of magnitude. A 150 ppm admixture of diborane yields “compensation”, i.e. adjusts the equation ( μτ ) n = ( μτ ) p = 5*10 −8 cm 2 /V. A pin solar cell with compensated i-layer is more red efficient than a cell with undoped i-layer.