Atomic Layer Deposition of Tin Monosulfide Thin Films

Abstract

Thin film solar cells made from earth-abundant, non-toxic materials are needed to replace the current technology that uses \(Cu(In,Ga)(S,Se)_2\) and \(CdTe\), which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (\(SnS\)). In this report, pure, stoichiometric, single-phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of \(bis(N,N′-diisopropylacetamidinato)tin(II)\) \([Sn(MeC(N-^{i}Pr)_{2})_{2}]\) and hydrogen sulfide \((H_2 S)\) at low temperatures (100 to 200 \(°C\)). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption \((\alpha > 10^4 cm^{−1})\) is observed throughout the visible and near-infrared spectral regions. The films are p-type semiconductors with carrier concentration on the order of \(10^{16} cm^{−3}\) and hole mobility \(0.82–15.3cm^{2}V^{−1}s^{−1}\) in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in-plane direction.