Title: 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 (Ge_xTe) 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>10^20cm^(-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 Ge_xTe and GeMn_xTe_y the effect is
much weaker than that observable in GeSb_xTe_y 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 Ge_xTe 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.