n-type electrical conduction in SnS thin films

TL;DR

This paper reports the first successful fabrication of n-type SnS thin films using RF-magnetron sputtering with Cl doping and sulfur plasma, enabling potential high-efficiency SnS homojunction solar cells.

Contribution

It demonstrates the first realization of n-type SnS thin films via a specific doping and deposition method, overcoming the p-type limitation of SnS.

Findings

N-type SnS films exhibit carrier concentrations of ~2 x 10^18 cm^-3.

Hall mobilities of the films range from 0.1 to 1 cm^2 V^-1 s^-1.

Sulfur plasma source is crucial for achieving n-type conduction.

Abstract

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. This study realizes n-type conduction in SnS thin films for the first time by using RF-magnetron sputtering with Cl doping and sulfur plasma source during deposition. N-type SnS thin films are obtained at all the substrate temperatures employed in this study (221-341 C), exhibiting carrier concentrations and Hall mobilities of ~2 x 10 18 cm-3 and 0.1-1 cm V-1s-1, respectively. The films prepared without 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 amount of acceptor-type defects originating from sulfur deficiency in p-type films, which appears as a broad optical absorption within the band gap. The demonstration of n-type SnS thin films in this study is a breakthrough for the realization of SnS homojunction solar cells, which are expected to have a higher conversion efficiency than the conventional heterojunction SnS solar cells.