Development of SnSe thin films through selenization of sputtered Sn-metal films

Abstract

Tin monoselenide (SnSe) thin films with thickness in the range of 0.72–1.00 μm were prepared by the two-stage process (metallization by sputtering + selenization by rapid thermal annealing) using Sn target and selenium powder at different selenization temperatures in the range of 300–450 °C. The formation of single-phase orthorhombic(OR)-SnSe films at ≥ 400 °C was observed, whereas the secondary phase of SnSe₂ in addition to OR-SnSe was formed when the films selenized at ≤ 350 °C. The single-phase OR-SnSe films exhibited Raman modes at 33 cm⁻¹, 71 cm⁻¹, 108 cm⁻¹, 130 cm⁻¹, and 151 cm⁻¹. The crystallinity and grain size of the OR-SnSe films were improved with increasing of selenization temperature. The tin films selenized at 400 °C showed the composition ratio of Se/Sn = 0.99, the direct bandgap energy of 1.2 eV, and the p-type conductivity with electrical resistivity of 12.71 Ω cm, the mobility of 2.03 cm² V⁻¹ s⁻¹, and carrier concentration of 2.42 × 10¹⁷ cm⁻³. The above opto-electronic properties of single-phase OR-SnSe films selenized at 400 °C indicated that these films could be used to attain good device efficiency of solar cells.