Changes in capacitance of amorphous Se:As alloy films during structural relaxation below the glass transition temperature

Abstract

Reversible hysteresis behavior of capacitance and ac conductance of amorphous Se:As alloy films (alloy range 0–4% As) below the glass transition temperature (Tg) is observed when measurements are carried out at fixed frequency in the temperature scan mode over an experimental range encompassing Tg. In this measurement mode, annealing effects which follow either cycling or film formation by evaporation can be continuously monitored, via film capacitance, as the film undergoes kinetically arrested isothermal relaxation toward a quasistable state. Arsenic addition to amorphous Se alters many of its physical properties. For example, in a previous study of the same series of films, it was found that both the dielectric increment measured just above their respective Tg ’s and the widths of the associated relaxation distribution function varied significantly with composition. In the present study, dielectric and thermodynamic measurements indicate that arsenic addition to amorphous Se significantly slows the rate of structural relaxation near room temperature (?15 K below respective Tg ’s). However, it is found that the shape of the capacitance relaxation function, associated in this case with structural relaxation below Tg, is relatively insensitive to alloy composition. The changes in room temperature relaxation, reflected in capacitance measurements, can in fact be adequately accounted for, phenomenologically, solely in terms of the shift in Tg induced by arsenic alloying. It is suggested (1) that dielectric relaxation in the melt above Tg and structural relaxation during annealing below Tg are controlled by a different set of dynamic processes or (2) progressive arsenic alloying skews the relaxation distribution function so that the very low frequency-spectral components which dominate relaxation below Tg remain unaffected.