Effects of Ge-and Sb-doping and annealing on the tunable bandgaps of SnS films

SnS, Ge- and Sb-doped SnS films with single orthorhombic SnS phase were fabricated via solvothermal routes and subsequent spin-coating, respectively. The substitution solubilities of Ge and Sb in SnS are about 6 and 5 at.%, respectively. The bandgaps of Ge- and Sb-doped SnS films can be tuned in the ranges of 1.25-1.35 and 1.30-1.39 eV, respectively. The possible mechanisms for the tunable bandgaps of Ge- and Sb-doped SnS films are discussed. For the Ge- and Sb-doped SnS films subjected to annealing at 200-350°C in N₂, the bandgaps of 200°C-annealed films remain unchanged, while those of 300°C- and 350°C-annealed films decrease with the annealing temperature because of the evaporation of Ge and Sb respectively.