STEADY-STATE PHOTOCONDUCTIVITY OF GALLIUM-DOPED AND INDIUM-DOPED HYDROGENATED AMORPHOUS-GERMANIUM THIN-FILMS

The effects of gallium and indium p-type doping on the photoconductivi ty of hydrogenated amorphous germanium (a-Ge:H) thin films deposited b y the rf-sputtering method are reported. The quantum efficiency-mobili ty-lifetime (eta mu tau) product was determined at room temperature as a function of the dark Fermi energy E-F on samples with a relative do pant concentration range between approximate to 3x10(-5) and approxima te to 10(-2). A decrease of eta mu tau is observed with the increase o f the Ga concentration until a minimum is reached for compensated samp les (E-F close to midgap level), where eta mu tau is about 16 times lo wer than the value obtained for intrinsic samples. This behavior is fo llowed by an eta mu tau increase as E-F crosses the midgap level. Then , for higher Ga doping levels, eta mu tau decreases again. For In-dope d samples, on the other hand, a monotonic decrease of eta mu tau is me asured for all the impurity concentration range. These results are con sistent with a model which assumes that the dangling bond is the main recombination path, and give independent evidence for the lack of corr elation between the defect density and E-F in p-type doped a-Ge:H. (C) 1998 American Institute of Physics.