COMMON FEATURES IN THE TRANSPORT BEHAVIOR OF DIVERSE GLASSY SOLIDS - EXPLORING THE ROLE OF DISORDER

Key results of time-of-flight drift mobility measurements on silicon and germanium backbone polymers are reviewed. Transport in these polymers displays a convoluted and yet familiar pattern of electric field and temperature dependences similar in remarkable detail to behaviour already reported for a very diverse collection of disordered molecular solids. The latter, while varied in composition and morphology, all share at least two common features, namely firstly transport controlled by interaction with localized states which are either hopping sites or shallow traps in communication with a band and secondly disorder. We explore in this paper the application of what is arguably the simplest model (derived from Monte Carlo simulation) of transport incorporating these characteristics. Consideration will be restricted to hopping among a spatially regular array of sites made energetically inequivalent by disorder. Thus, neither positional disorder nor site relaxation is explicitly considered. Some reformulation of experimental data is carried out to facilitate critical comparison with predictions of the model. It is demonstrated that both the commonly observed Poole-Frenkel-like field dependence of drift mobility and the transit pulse widths (always well in excess of that predicted by simple diffusion) can be simultaneously accounted for in terms of a single disorder parameter. The disorder parameter can in turn be directly related to the distribution of transport interactive states.