n-Type Electrical Conduction in SnS Thin Films

Tin monosulfide (SnS) usually exhibits p-type conduction due to the low formation enthalpy of acceptor-type defects, and as a result, n-type SnS thin films have never been obtained. In this paper, we realize n-type conduction in SnS thin films by using radiofrequency-magnetron sputtering with Cl doping and a sulfur plasma source during deposition. Here, n-type SnS thin films are obtained at all the substrate temperatures employed in this paper (221-341 °C), exhibiting carrier concentrations and Hall mobilities of ∼2×1018cm-3 and 0.1-1cm2V-1s-1, respectively. The films prepared without a sulfur plasma source, on the other hand, exhibit p-type conduction despite containing a comparable amount of Cl donors. This is likely due to a significant number of acceptor-type defects originating from sulfur deficiency in p-type films, which appears as a broad optical absorption within the band gap. We demonstrate n-type SnS thin films in this paper for the realization of SnS homojunction solar cells, which are expected to have a higher conversion efficiency than the conventional heterojunction SnS solar cells.