Effect of substrate temperature on the characteristics of mixed phase SnTexSe1−x (x = 0.32) thin films

Abstract

Thermal evaporation from an alloyed SnTe0.32Se0.68 source forms thin film with mixed Te and SnSe constituent phases due to incongruent evaporation. The Te crystallites in hexagonal phase are identified by (1 0 0), (1 0 1) and (1 1 0) diffraction planes and SnSe in orthorhombic phase as evidenced by (4 0 0), (5 1 1), (5 0 2) and (3 2 2) diffractions. The Te crystallites increase with increase in the substrate temperature (Ts) upto 353 K thereafter decrease and disappear at 553 K. The reduction and disappearance of Te crystallites are attributed to thermal dissociation and re-evaporation of Te from the film phase. The increase in Ts led to increase in SnSe from nearly nonexistent at 300 K to dominant crystallite phase at 503 K and minimal decline at 553 K. SEM studies showed nanosize Te flake-like crystallites embedded in spherical SnSe crystallites. Thus, substrate temperature affects film microstructure and the atomic concentration of SnSe and Te in the film phase. This reflects variation in the direct band gap of deposited films from 0.76 to 1.07 eV and corresponding absorption coefficient from 3.5 × 104 to 9.0 × 104 cm−1 randomly with substrate temperature. All films showed p-type conduction with increase in resistivity from 7.84 × 10−3 to 1.09 Ω cm and corresponding decrease in hole mobility from 40.5 to 2.9 cm2 V−1 s−1 and hole concentration from 1.97 × 1019 to 1.9 × 1018 cm−3 as substrate temperature increases from 300 to 503 K.