Atomic Layer Deposition of Tin Monosulfide Thin Films

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-iPr)2)2] and hydrogen sulfide (H2S) at low temperatures (100 to 200 degrees C). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption (a > 104 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 1016 cm-3 and hole mobility 0.8215.3 cm2V-1s-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.