Temperature Dependence of the Field-Effect Conductance in Thin Polycrystalline CdS Films

Abstract

The field‐effect conductance and the capacitance‐voltage characteristics of thin‐film, polycrystalline CdS–SiO₂–Al field‐effect structures were measured as a function of temperature in the range from 100° to −50°C, and mechanical stress because of differential thermal expansion. It was concluded that (1) the channel mobility varies exponentially with temperature with an activation energy of the order of 0.06 eV, which corresponds to the height of the intercrystalline barriers at the grain boundaries, (2) the channel mobility increases with the induced charge‐carrier density, (3) the flat‐band voltage varies linearly with temperature at a rate of the order of 0.01 V/deg, which corresponds to an interface state density of the order of 10¹³ cm⁻² eV⁻¹ in the bandgap in the vicinity of the conduction band, (4) the flat‐bond voltage increases with compressive stress at a rate as high as several hundred volts per percent strain and (5) contact barriers between the source and drain electrodes and the surface channel become significant at temperatures below −25°C.