Microstructural control by substrate heating in Pulse-DC sputtering induced thermoelectric Ge2Sb2Te5 thin films

Highlights: • Ge₂Sb₂Te₅ thin films were successfully microstructural controlled by substrate heating. • Microstructural of Ge₂Sb₂Te₅ thin films were controlled for thermoelectric properties. • Thermoelectric properties were discussed based on temperature of substrate heating. Optimization of substrate heating during sputtering processes is essential to obtain desired microstructures of deposited thin films, as it provides the required energy flux during the nucleation and growth. In this work, Ge₂Sb₂Te₅ thin films were prepared by a pulsed-DC magnetron sputtering process at optimized plasma conditions (pulsed frequency and pulse reversal time). The effect of substrate heating, in temperature range of 250–450 °C, was systematically investigated on the process throughput and various properties i.e. microstructure, morphology, atomic composition, carrier concentration, mobility and Seebeck coefficient of deposited films. The substrate heating was found to be required to obtain films in cubic crystalline phase. Through the optimization of substrate temperature, process throughput and surface properties, electrical properties as well as thermoelectric power factors were enhanced. The maximum power factor value of thin films was achieved as 0.77 mW m^–1 K^–2 for the substrate temperature as 400 °C.