Temperature dependent dielectric properties of GeTe-rich (GeTe)x(Sb2Te3)1−x glass

Abstract

The dielectric properties of phase-change materials, which could switch between crystalline and amorphous states, determine the device performances in the electronic and optical applications. Here, we have systematically investigated the dielectric properties of amorphous (a-) Ge8Sb2Te11 thin films with temperature by two complementary methods, i.e., the AC electrical measurement (0.5–186 Hz) and the impedance spectroscopy (9 kHz–3 GHz). The characterization of dielectric behavior of a-Ge8Sb2Te11 at low frequencies approaching DC, as defined by the static dielectric constants (εst), is achieved by the measurement at very low temperature. The resulting εst of a-Ge8Sb2Te11 is much larger than its optical dielectric constant ε∞ at room temperature, which is mainly ascribed to the contribution of infrared active phonons at around tens of meV. The εst increases linearly by 16.5% from 5 to 300 K, due to more optical phonons activated at elevated temperatures. We also notice that εst shows little dependence on the frequency, and the total conductivity of a-Ge8Sb2Te11 extracted from impedance spectroscopies is frequency independent up to 10 MHz. Hence, no obvious dielectric relaxations are observed in a-Ge8Sb2Te11 below 10 MHz close to room temperature. In addition, the bandgap calculated from temperature dependence of the electrical conductivity is larger than that measured from the optical absorption edge by 11.5%.