Thermoelectric Power Factor Enhancement by Pulsed Plasma Engineering in Magnetron Sputtering Induced Ge₂Sb₂Te₅ Thin Films

Abstract

Precise control over microstructure and composition is desired prerequisite for the performance enhancement of thermoelectric materials. In conventional magnetron plasma sputtering synthesis, composition control is challenging when the sputtering-target is composed by different elements. Here, the potential of pulsed power utilization is demonstrated for compositional control of Ge2Sb2Te5 thin films via pulse-reversal time and pulse-frequency engineering in pulsed DC-magnetron sputtering process. When annealed at 400 °C for 1 h in vacuum conditions, amorphous thin films (of 200 nm thickness, deposited on glass substrate) crystallize in to face centered cubic phase with average nanocrystallite size ∼10 nm. Power density enhancement to 5.56 W/cm2 at low pulse reversal time induces maximum process throughput as 450 nm/min. Increase in either of pulse frequency or pulse reversal time decreases the discharge voltage and plasma density. As a consequence, kinetic energy of ions and ionization of plasma species are sequentially controlled to improve the stoichiometry of film and eventually; the electronic transport. The optimization of pulse plasma engineering yields maximum thermoelectric power factor value as 1.35 μW cm–1 K–2 with process throughput more than 300 nm/min. The obtained values are promising for applications in the automobile and microelectronics industry.