Capacitance-voltage measurements of Ge-Sb-Te thin films

The capacitance-voltage (C-V) measurements of Ge₂Sb ₂Te₅ thin films were performed for a sweep of voltages from -20 to +20 V at different temperatures. Amorphous and crystalline samples of Ge₂Sb₂Te₅ thin films were used to investigate the effects of temperature, bias voltage and frequency on their capacitances. The capacitance decreases as the bias voltage increases for both amorphous and crystalline samples. This effect has been observed at all temperatures in the crystalline sample, while in the amorphous sample the effect appears only at temperatures close to the amorphous-crystalline transition temperature. Negative capacitance values are observed in the crystalline sample at high bias voltage. This effect may be attributed to the change in the conduction from p- to n-type when the bias voltage or the temperature is increased up to certain appropriate values. The effects of bias voltage and temperature are frequency dependent and they are more pronounced at 100 kHz than at 1 MHz.