Films*

Tungsten disulphide (WS₂) is of particular interest in optoelectronics because of the band gap transition from indirect to direct as the crystal thickness is reduced from bulk to a single layer [1]. To achieve large area coverage suitable for industrial applications, growth methods such as chemical vapour deposition (CVD) need to the developed. Current powder-based CVD approaches [2] produce crystalline flakes that are useful for fundamental studies but cannot produce continuous wafer scale films [3]. In this work, we produce continuous and uniform thin films of WS₂ via MOCVD techniques at scales up to 200mm wafer sizes.
Our films are deposited at 600C using a tungsten hexachloride precursor gas and a hydrogen sulphide sulphur source. Raman spectroscopy and photoluminescence (PL) measurements demonstrate high quality as-grown WS₂ thin films on sapphire substrates. We further show how a post-growth annealing step in H₂S quenches sulphur vacancy sites in the WS₂ and dramatically increases the PL intensity.
[1] A. Kuc et al., Physical Review B, 83, 245213, 2011
[2] McCreary KM et al., Scientific Reports, 6, 19159, 2016
[3] Kang. K et al., Nature, 520, 656-660, 2015