Transport properties of nitrogen-doped hydrogenated amorphous germanium films

This paper discusses experimental data referring to the electronic properties of N-doped hydrogenated amorphous germanium films (a-Ge:H). The a-Ge:H films, prepared by rf sputtering, possess a low density of electronic states in the pseudogap (in the low ${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$ range) and exhibit a temperature-activated dark conductivity down to below 200 K. It is shown that N atoms incorporated into the a-Ge:H films produce large changes of both the room-temperature dark conductivity and the activation energy. The results of the present work are consistent with the overall picture of the active doping mechanism of group-V elements in tetrahedrally coordinated amorphous semiconductors. The donor level introduced by fourfold-coordinated nitrogen in a-Ge:H is found to be around 50 meV below the conduction-band edge.