Conductance relaxation in GeBiTe - slow thermalization in an open quantum system

TL;DR

This paper investigates the out-of-equilibrium electronic behaviors of GeBiTe films, revealing persistent photoconductivity and electron-glass effects, with detailed analysis of their relaxation dynamics and the interplay between these phenomena.

Contribution

It provides the first detailed study of the coexistence and distinct relaxation laws of PPC and electron-glass effects in GeBiTe, highlighting their dependence on disorder and interactions.

Findings

PPC persists across all sheet resistances studied.

Memory-dip is the widest among germanium-telluride alloys.

Relaxation laws for PPC and electron-glass effects are distinctly different.

Abstract

This work describes the microstructure and transport properties of GeBiTe films with emphasis on their out-of-equilibrium behavior. Persistent-photoconductivity (PPC), previously studied in the phase-change compound GeSbTe is also quite prominent in this system. Much weaker PPC response is observed in the pure GeTe compound and when alloying GeTe with either In or Mn. Films made from these compounds share the same crystallographic structure, the same p-type conductivity, a similar compositional disorder extending over mesoscopic scales, and similar mosaic morphology. The enhanced PPC response exhibited by the Sb and Bi alloys may therefore be related to their common chemistry. PPC is observable in GeBiTe films at the entire range of sheet resistances studied in this work. The excess conductance produced by a brief exposure to infrared illumination decays with time as a stretched-exponential (Kohlrausch law). Intrinsic electron-glass effects on the other hand, are observable in thin films of GeBiTe only for samples that are strongly-localized just like it was noted with the seven electron-glasses previously studied. These include a memory-dip which is the defining attribute of the phenomenon. The memory-dip in GeBiTe is the widest among the germanium-telluride alloys studied to date consistent with the high carrier-concentration of this compound. The thermalization process exhibited in either, the PPC-state or in the electron-glass regime is sluggish but the temporal law of the relaxation from the out-of-equilibrium state is distinctly different. Coexistence of the two phenomena give rise to some non-trivial effects, in particular, the visibility of the memory-dip is enhanced in the PPC-state. The relation between this effect and the dependence of the memory-effect magnitude on the ratio between the interparticle-interaction and quench-disorder is discussed.