Temperature dependence of capacitance-voltage characteristics of germanium telluride thin films

Temperature-dependent capacitance-voltage and conductance-voltage measurements of 200-nm-thick germanium telluride (GeTe) thin films deposited via direct current magnetron sputtering were investigated. Measurements were performed across a temperature range of 27-357 °C, with a sweep of voltage values from -20 to +20 V at an operating frequency of 1 MHz. An amorphous-crystalline transition temperature (Tc) of 197 °C was found. Below Tc, the GeTe films were highly resistive, and their capacitance was insensitive to the applied bias voltage and temperature. Above Tc, the capacitance showed strong dependence on temperature, owing to the triggering of GeTe crystallization incorporating nucleation and growth processes. Applied bias voltage did not show a profound impact on the GeTe capacitance even after crystallization, but it had an observable impact on the film conductance beyond 250 °C. Moreover, the GeTe thin film capacitance increased by a factor of 13 upon crystallization. Hall-effect measurements revealed that the film conductivity increased upon crystallization, as did the hole concentration and mobility. Cross-sectional transmission electron microscopy demonstrated that the GeTe thin films crystallize via a nucleation-dominated crystallization mechanism.