Germanium telluride undergoes rapid transition between polycrystalline and amorphous states under either optical or electrical excitation. While the crystalline phases were predicted to be semiconductors, polycrystalline germanium telluride always exhibited p-type metallic conductivity. A study was made of the electronic structure and formation energies of the vacancy and antisite defects in both known crystalline phases. It was shown that that these intrinsic defects determine the nature of free-carrier transport in crystalline germanium telluride. Germanium vacancies require roughly one-third the energy of the other three defects to form, making this by far the most favourable intrinsic defect. While the tellurium antisite and vacancy induce gap states, the Ge counterparts do not. A simple counting argument, reinforced by integration over the density of states, predicts that the Ge vacancy leads to empty states at the top of the valence band, thus giving a complete explanation of the observed p-type metallic conduction.

Electronic Structure of Intrinsic Defects in Crystalline Germanium Telluride. A.H.Edwards, A.C.Pineda, P.A.Schultz, M.G.Martin, A.P.Thompson, H.P.Hjalmarson, C.J.Umrigar: Physical Review B, 2006, 73[4], 045210 (13pp)