Threading dislocations in germanium thin films on silicon introduce acceptor states in the germanium bandgap close to the valence band. Thus, highly defected germanium thin films spontaneously exhibit a p-type behavior. Here we report on spin-on-dopant diffusion of phosphorus in thermally evaporated, highly defected germanium thin films. We demonstrate effective compensation of the acceptor states associated to dislocations by means of post-growth doping.
We discuss phosphorus diffusion in these highly defected films and pinpoint the benefits of spin-on-doping by realizing and testing near-infrared photodiodes in evaporated Ge on Si, achieving high responsivities which compare well with those of state-of-the-art Ge p-i-n photodiodes. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)