Theory of Persistent, P-Type, Metallic Conduction in C-GeTe
AIR FORCE RESEARCH LAB KIRTLAND AFB NMSPACE VEHICLES DIRECTORATE
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It has been known for over 20 years that rhombohedral c-germanium telluride is predicted to be a narrow gap semiconductor. However, it always displays p-type metallic conduction. This behavior is also observed in other chalcogenide materials, including Ge2Sb2Te5, commonly used for optically and electrically switched, non-volatile memory, and so is or great interest. We present a theoretical study of the electronic structure or the perfect crystal and of the formation energies of germaniumtellurium vacancy and antisite defects in rhombohedral germanium telluride. We find that germanium vacancies are by far the most readily formed defect, independent of Fermi level and of growth ambient. Moreover, we predict that the perfect crystal is thermodynamically unstable. Thus, the predicted large equilibrium densities of the germanium vacancy of 5 x 10exp 19 cmexp -3 results in a partially filled valence band and in the observed p-type conductivity.
- Inorganic Chemistry