Structural and thermoelectrical characterization of epitaxial Sb2Te3 high quality thin films grown by thermal evaporation
Thermal evaporation of Sb2Te3 powder was systematically studied under various pressure and temperature conditions. Low pressure experiments (5 10−6 mbar) conducted inside a horizontal tube reactor at a temperature range of 500 °C–600 °C generated rough polycrystalline films on Si(100) substrates. Based on these experiments, the chemical composition of the resulting films were determined by the furnace temperature. Enhancing the reactor pressure to 20 mbar shifted the growth zone towards higher temperature ranges and yielded highly c-oriented Sb2Te3 films on Si(100) and Al2O3(0001) substrates. Additional experiments were conducted inside a special reactor containing two independent heaters to study the effects of the evaporator and substrate temperatures independently. In contrast to the samples generated in the previous reactor, a two-zone heating reactor allowed the growth of epitaxial Sb2Te3 films with a very smooth surface topology on Al2O3(0001) substrates, as shown by SEM, EDX, XPS, and HRTEM. The electrical in-plane conductivity of the Sb2Te3 films decreased with increasing temperature, ultimately reaching 3950 S cm−1 at 300 K. The films showed a p-type carrier concentration of 4.3 10−19 cm−3 at 300 K and a very high carrier mobility of 558 cm2 V−1 s−1. The Seebeck coefficient increased monotonically from 94 μV K−1 at 270 K to 127 μV K−1 at 420 K.