Preparation of Phosphorus-Doped Si0.8Ge0.2 Thermoelectric Thin Film Using RF Sputtering with Induction Coil

Abstract

A phosphorus-doped Si0.8Ge0.2 thin film of 300 nm thickness was deposited by radio-frequency (RF) sputtering with an induction coil. Thermal annealing was carried out to crystallize as-deposited amorphous-like SiGe thin films. The thermoelectric properties of the thin films, such as electrical conductivity, carrier concentration, mobility and Seebeck coefficient, were investigated. After annealing at 1000°C for 5 h, the Si0.8Ge0.2 thin films exhibited fine grains of around 30 nm and a smooth surface with an RMS of 1.91 nm. With increasing annealing time, the crystallization of the films progressed, resulting in a high carrier mobility and a large absolute Seebeck coefficient. The phosphorus-doped Si0.8Ge0.2 thin film annealed at 1000°C for 50 h showed a low resistivity of 0.04 Ωcm, a large Seebeck coefficient of -0.29 mV/K, a Hall mobility of 5.41 cm2/Vs, and a carrier concentration of 2.7×1019 cm-3 at 100°C. The low resistivity of the Si0.8Ge0.2 thin film in this study was achieved by strong doping with RF sputtering using the induction coil and resulted in a relatively large thermoelectric power factor of 1.9×10-3 W/K2m, which is the same as that obtained by CVD.