Abstract
In this paper we report the growth of high quality SnS thin films with good crystallinity deposited on two-dimensional (2D) mica substrates. It is believed that the 2D nature of SnS, with strong intra-layer covalent bonds and weak inter-layer van der Waals interactions, is responsible for its relative insensitivity to lattice mismatch. We also investigated the reduction of Sn vacancies in the material using Sn-compensation technique during the material growth process. The experimental results clearly demonstrated substantial enhancements in the electrical and structural properties for films deposited using Sn-compensation technique. A mobility of 51 cm2 V−1 s−1 and an XRD rocking curve full width at half maximum of 0.07° were obtained. Sn-compensated SnS/GaN:Si heterojunctions were fabricated and significant improvement in both the I-V characteristics and the spectral responsivities of the devices were characterized.
Highlights
In this paper we report the growth of high quality SnS thin films with good crystallinity deposited on two-dimensional (2D) mica substrates
The two-dimensional (2D) structure of SnS is of particular interest due to the fact that the material consists of strong fully saturated intralayer covalent bonds, but across the unit layers the interaction is dominated by weak van der Waals force[3,4]
The SnS films were prepared in an SVT 35N molecular beam epitaxy (MBE) system, which provides a highly versatile research tool that enables one to systematically vary the growth parameters with high repeatability
Summary
The SnS films were prepared in an SVT 35N MBE system, which provides a highly versatile research tool that enables one to systematically vary the growth parameters with high repeatability. From the point of view of energy band theory, when the Sn vacancies in the film are filled and the carrier concentration decreases, the Fermi level of SnS thin film will shift upwards, reflected by the slight decrease in work function deduced from the UPS spectra and the increase in (EVBM −Ef) extracted from the XPS spectra. The work function difference between the SnS and GaN will be narrowed, leading to the slight decrease in Voc. The observed enhancement in the photocurrent is attributed to the reduction in the trap density due to Sn vacancies by the extrinsic Sn atoms and, thereby, the enhancement in the minority carrier diffusion length in the absorbing layer. Excessive incorporation of Sn atoms in the SnS layer results in the segregation of Sn atoms, which leads to a degradation in the device performance
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