Local order of Sb and Bi dopants in hydrogenated amorphous germanium thin films studied by extended x-ray absorption fine structure

This letter reports on the investigation of the local order and coordination of Sb and Bi impurities in hydrogenated amorphous germanium thin films. The study uses the extended x-ray absorption fine structure technique in fluorescence mode at room temperature. The investigation includes doping concentrations ranging from 1.1 x1019 to 5 x1020 cm-3. For both impurities, the evidence is that the thermal equilibrium model is not applicable in this case. This result qualitatively follows the behavior of Ga and In impurities in hydrogenated amorphous germanium (a-Ge:H) samples except for Bi. These findings are consistent with data on the transport properties of Sb- and Bi-doped a-Ge:H films.