Dopant impurity-induced defects in p-type doped hydrogenated amorphous germanium

The defect density (N-D) in hydrogenated amorphous germanium (a-Ge:H) doped p-type by aluminum, gallium, or indium was studied as a function of the dopant impurity concentration (N-imp) by using photothermal deflection spectroscopy. N-D remains roughly constant with increasing N-imp for N-imp < 2 x 10(19) cm(-)3 and increases linearly for larger N-imp for Al, Ga, or In doping, On the other hand, the dependence of N-D on the Fermi energy (as deduced from conductivity measurements) is different for the different dopant impurities, contrary to predictions of charge-induced weak bond-dangling bond conversion models. A mechanism involving direct dangling bond formation induced by sp(2) bonded dopant impurities qualitatively accounts for the observed results. (C) 1996 American Institute of Physics.