Fabrication of single-phase SnS film by H-2 annealing of amorphous SnSx prepared by atomic layer deposition

Abstract

This study evaluated a simple and novel route to fabricate single-phase SnS thin films, consisting of the growth of smooth amorphous SnS2 films by atomic layer deposition at very low temperature using tetrakis(dimethylamino) tin {TDMASn, [(CH3)(2)N](4)Sn} and hydrogen sulfide followed by H-2 annealing at controlled higher temperatures. The properties of the SnS films fabricated by subjecting the amorphous as-grown SnS2 films deposited at 100 degrees C to post-H-2 annealing at 360 degrees C were superior to those of the as-grown SnS films deposited at 200 degrees C in terms of their phase purity, optical band gap, adhesion, and surface roughness. Raman spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and atomic force microscopy consistently showed that single-phase, stoichiometric crystalline (orthorhombic structure) SnS films (Sn/S ratio: similar to 1), without any incorporated sulfur-rich tin sulfides, could be fabricated with a very low surface roughness [root mean square (RMS) roughness: similar to 7 nm] using the proposed scheme. On the other hand, the as-grown SnS film at 200 degrees C still contained a small amount of SnS2 phase and its RMS surface roughness was as high as 16 nm. The optical band gap of the as-grown SnS film was 1.85 eV, whereas that of the annealed SnS film was similar to 1.2 eV, confirming the latter's improved phase purity. The SnS film fabricated by H-2 annealing was a p-type semiconductor with a carrier concentration of similar to 2.3 x 10(16)/cm(3) and a hole mobility of similar to 15 cm(2)/Vs. The present scheme to prepare high-quality SnS films might be useful for fabricating photovoltaic or solar conversion devices. (C) 2017 American Vacuum Society.