Nonequilibrium transport and Electron-Glass effects in thin GexTe films
Abstract
We report on results of nonequilibrium transport measurements made on thin films of germanium-telluride (GexTe) at cryogenic temperatures. Owing to a rather large deviation from stoichiometry (app. 10% of Ge vacancies), these films exhibit p-type conductivity with carrier-concentration N>1020cm(-3) and can be made either in the diffusive or strongly-localized regime by a judicious choice of preparation and post-treatment conditions. In both regimes the system shows persistent photoconductivity following excitation by a brief exposure to infrared radiation. Persistent photoconductivity is also observed in GexTe samples alloyed with Mn. However, in both GexTe and GeMnxTey the effect is much weaker than that observable in GeSbxTey alloys suggesting that antimony plays an important role in the phenomenon. Structural studies of these films reveal an unusual degree of texture that is rarely realized in strongly-disordered systems with high carrier-concentrations. Anderson-localized samples of GexTe exhibit non-ergodic transport which are characteristic of intrinsic electron-glasses, including a well developed memory-dip and slow relaxation of the excess conductance created in the excited state. These results support the conjecture that electron-glass effects with inherently long relaxation times is a generic property of all Anderson-localized systems with large carrier-concentration.