In2O3 seed layer-assisted growth of cubic SnS thin films using atomic layer deposition

Abstract

In this study, we demonstrate the fabrication of highly crystalline, single-phase, cubic tin monosulfide (SnS) thin films using an indium oxide (In2O3) seed layer, achieving phase stability even after high-temperature annealing. The In2O3 seed layer was deposited by atomic layer deposition (ALD) using [3-(dimethylamino)propyl]dime-thylindium (DADI) and ozone (O3), followed by oxygen (O2) annealing to enhance crystallinity and maximize the template effect. The deposition process was optimized using X-ray reflectometry (XRR), while thin film composition was analyzed by Auger electron spectroscopy (AES). Grazing incidence X-ray diffraction (GI-XRD) confirmed the cubic In2O3 structure after annealing. X-ray photoelectron spectroscopy (XPS) was used to analyze its chemical bonding states. Water contact angle (WCA) measurements indicated that the In2O3 seed layer provided a favorable surface energy. SnS thin films (5 nm, 10 nm, 15 nm) were deposited on In2O3 seed layer to evaluate the seed layer effect, and in situ annealing was performed. GI-XRD, Raman spectroscopy (Raman), and transmission electron microscopy (TEM) confirmed the stability of the cubic phase. Energy dispersive X-ray spectroscopy (EDX) showed no elemental diffusion between SnS and In2O3, and XPS analysis showed a higher binding energy for cubic-phase SnS compared to its orthorhombic phase. This was attributed to differences in coordination number. Ultraviolet-visible spectroscopy (UV-vis) and ultraviolet photoelectron spectroscopy (UPS) confirmed that all SnS films showed p-type characteristics, with cubic SnS exhibiting a higher bandgap. These findings highlight the role of the In2O3 seed layer in stabilizing and enhancing the crystallinity of cubic SnS thin films.