Synthesis of submillimeter SnSexS2−x (0 < x < 1) two-dimensional alloy and photoinduced reversible transformation between Schottky and Ohmic contact behaviors in devices

Abstract

The large-scale controllable synthesis of high-quality alloyed semiconductors with a precise composition and electronic modulation is of great importance for their application in electronics and optoelectronics. Here, we demonstrate the direct synthesis of two-dimensional SnSe_xS_2−x alloy via the chemical vapor deposition (CVD) technique. The size of single-crystal flakes could reach up to 750 μm, ten times larger than the previously reported CVD grown SnS₂ and SnSe₂. The morphology of the atmospheric pressure CVD grown SnSe_xS_2−x flakes revealed an evolution from semi-hexagon to semi-circle as the content of Se atoms increased, while the low-pressure CVD alloyed flakes kept a constant semi-hexagon shape. UV-visible spectroscopy and PL measurement revealed adjustability of bands in the alloy flakes, where a higher Se atom content caused a narrower band gap. The SnSe_xS_2−x devices demonstrated a high I_light/I_dark ratio under switching between light and dark, whose rise and fall times were just 225.9 μs and 646.2 μs, respectively. More importantly, the devices showed Schottky-contact behaviour under dark conditions, which changed to Ohmic under illumination, leading to a tunable I_light/I_dark ratio controlled by the bias voltage between drain and source electrodes. This work helps the large-area growth technique and unique electrical property improvement of two-dimensional alloys to get closer to practical applications.