Effect of substrate and annealing temperature on the physical properties of the thin films of SnSe2-SnSe alloy

Abstract

Thin films of SnSe2-SnSe alloy were deposited at substrate temperatures 300 and 473 K by thermal evaporation. The 473 K as-deposited layers were re-grown on annealing from 523 to 623 K. The films show mixed phases of hexagonal SnSe2 and orthorhombic SnSe and display corresponding vibrational modes. The unit cell parameters and axes strain of the layers vary and show crystallite size distributions with changes in annealing temperature (Ta). Moreover, the film smoothness increases at elevated temperatures. The films as-deposited at 300 K exhibit direct bandgaps (Eg) of 1.15 and 1.52 eV. Further, the Eg values of 473 K layers vary from 1.47 to 1.56 eV with a change in temperature from 523 to 623 K and show an absorption coefficient (α) ≥ 5 × 104 cm−1. In addition, the refractive index (n) decreases, and optical mobility (μopt) increases with an increase in Ta. The above optical response indicates the films to be optically active and suitable in photonic devices in the visible and NIR portion of the EM spectrum. The PL emission peaks were observed at 805.1 and 1064.22 nm, which confirmed the presence of direct bandgaps of the SnSe2 and SnSe phases.