Giant figure of merit (ZT) of Ge2Sb2Te5 thin films through the control of crystal structure

300nm-thick Ge2Sb2Te5 Thin Films were prepared using RF sputtering with different deposition temperatures. Thermoelectric properties of GST thin films were measured at room temperature including the Seebeck coefficient, the electrical conductivity and thermal conductivity. The highest power factor (1.1 × 10-3 W/K2m) was shown in the GST film deposited at 250°C, which has the mixture phases of FCC and HCP structure. And the moderate degree of electrical conductivity and the Seebeck coefficient in the GST film deposited at 250°C lead to the highest ZT value of nearly 2.0. In order to explain giant ZT value, the crystal structure, the electrical parameters and the chemical composition were investigated.