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Time-of-flight drift mobility experiments have been carried out on pure and chlorine-doped amorphous selenium films. The temperature and field dependence of the drift mobility of both types of carriers have been investigated and the charge transport mechanism has been critically examined in terms of various shallow-trap-controlled transport processes, including hopping for the microscopic mobility. Addition of 30 and 40 wt ppm Cl to a-Se has been found to increase the hole drift mobility activation energy by approximately 0.16 eV. Two interpretations have been shown to be plausible: (i) Cl doping diminishes the existing charged centres (possibly Se1-) acting as shallow hole traps and/or changes the mode of microscopic transport, (ii) Cl introduces a new set of charged hole traps (probably Cl-) at approximately 0.45 eV above Ev. Furthermore, it is shown that at low temperatures the hole drift mobility may be described by an empirical expression similar to that due to Gill (1972, 1976).

The theoretical basis of thermal analysis of crystallization kinetics occurring by nucleation and growth under non-isothermal conditions of constant heating rate / 3 has been studied by integrating the fundamental equation describing the crystallized volume fraction, x. Assuming a thermally activated growth rate of the form u = uo exp ( -E , / k T ) two specific cases have been considered: (i) growth from a constant number of nuclei or growth following the saturation of nucleation sites and (ii) a temperature-dependent nucleation rate whose functional form over a limited temperature range is approximated by I, = lo exp ( -E N / k T ) .It is shown that the expression for the crystallized fractional volume x ( T ) contains a function ( P, , of the initial temperature To. Except for one-dimensional growth under case (i), the rate of transformation x is also a function of To, which implies that a Johnson-Mehl-Avrami type of description of the kinetics is inappropriate.The limits of applicability of current thermoanalytical methods of the following groups: Kissinger, Borchardt-Piloyan, Ozawa, Chen and Coats-Redfern-Sestak, have been critically examined and modifications have been proposed to include the effect of the initial temperature. A method of thermal analysis has been developed to determine the nature of the crystallization kinetics.

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