Gallium oxide (Ga2O3) is a promising ultra-wide bandgap (UWBG) semiconductor that was quickly recognised as a suitable material for fabrication of optoelectronic devices or high-power rectifiers and switches, potentially greatly exceeding the capabilities of mainstream Si, GaN, and SiC. Despite many advantageous material properties, large-area bulk Ga2O3 substrates remain expensive, and Ga2O3 itself suffers from low lattice thermal conductivity – crucial for an efficient heat extraction from the active device area, generated by Joule losses during the on-state operating conditions. Heteroepitaxy of Ga2O3 films offers a possible route for a low-cost production of Ga2O3-based power or optoelectronic devices if e.g. sapphire substrates are used, or much improved thermal performance if highly-thermally-conductive substrates such as SiC or polycrystalline diamond are used. In this work we use liquid-injection metalorganic chemical vapour deposition (LI-MOCVD) to grow thin Ga2O3 films on sapphire and 4H-SiC and to fabricate depletion-mode metal-oxide-semiconductor field-effect transistors (MOSFETs). Structural and transport properties of the Ga2O3 films and devices prepared on both substrates are analysed. Then, thermal properties of grown Ga2O3 films, and Ga2O3/SiC and Ga2O3/sapphire interfaces are presented and implications for Ga2O3-based devices are outlined.
Sulfurization of a Mo layer is one of the most used methods for preparation of thin MoS2 films. In the method, a sulfur powder and Mo covered substrate are placed in different positions within a furnace, and heated separately. This requires a furnace having at least two zones. Here, we present a simplified version of the method where a one-zone tube furnace was used. A molybdenum film on a substrate and a sulfur powder were placed in the center of the furnace and heated at temperatures above 800°C. Mo films transform into MoS2 in vapors of sulphur at high temperatures. As-prepared films were characterized by number of techniques including X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman, Rutherford backscattering (RBS) and X-ray photoelectron spectroscopy (XPS). It appears that one-zone sulfurization, with just one annealing temperature used, is a suitable method for fabrication of MoS2 thin films. This method is fast, cheap and easy to scale up.
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