Critical dimensions of MoS2, WS2 and WO3 thin films: Potential Photovoltaic Applications

Abstract

The study of the materials molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2), and tungsten trioxide (WO3) in the form of a thin film is of great relevance, primarily to understand their physicochemical properties to design photovoltaic applications. The samples were made using a Kurt J. Lesker PVD75© equipment by RF-sputtering at 225 Watts using commercial targets of WO3 (99.95%) and MoS2, MoSe2 (99.9%) on sapphire substrates and silicon dioxide under atmospheric pressure conditions of 1.3 X 10-4 Pa at a deposition rate of 1Å/s. Only for the WO3 samples, post-deposit annealing was used in a Qualiflow-Jiplec Jetfirst100© brand furnace under atmospheric conditions of 3%H2/N2 formation gas with a ramp of 1°C/s up to temperatures of 300°C, 400° C, 500°C and 550°C for a period of 45 minutes, followed by natural cooling. Using an Ambios XP-2© brand profilometry equipment, layer thicknesses of 200 to 300 nm were determined. Subsequently, using the scanning electron microscopy technique with Hitachi S-5500© equipment, aspects related to surface topography; from this, we could obtain the chemical composition of W, O, Mo, S, In, and Sn as contained on the prepared samples. In addition, atomic force microscopy was used only for WO3 samples in order to obtain piezoresponse domains by spectroscopy using an AC resonance with aid of Infinity 3D Asylum Research® unit. The piezoresponse measurements have been carried out in vertical and amplitude mode with 5Vpk-pk voltage at 398 kHz frequency and hysteresis loops were recorded at range of -10V to 10V. Both fabricated samples of MoS2/MoSe2 and WO3 were analyzed using atom probe tomography for inspection of 3D chemical composition. APT reveals a low concentration of selenium ions at the MoS2 layer and forming gas nanovoids in WO3. Using density functional methods it was possible to determine electronic structure of ITO-MoS2 and MoS2/MoSe2 in order to describe energy band gap near Fermi energy level. Finally, our studies provide scientific knowledge in semiconductor materials for its use reengineering a more efficient and low-cost microelectronic devices, positively influencing the field of energy and climate change.