The structure, electronic and optical properties of 3C-SiC nano films were calculated according to first principles based on density functional theory. It is manifested that the nano films were structurally stable when the number of layers was increased to 12. Compared with bulk counterparts, nano films displayed narrower band gaps, and their Fermi energy levels were brought into the conduction band. The ε 2 (ω) of dielectric function, extinction coefficient, and absorption coefficient of the nano films were greater than that of the bulk in the ultraviolet range. With the layer numbers decreased, the values increased in the range. The results provide a guideline for 3C-SiC nano films to work for UV detectors.

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Photogalvanic etching, or photo-assisted electroless etching, is a simple wet-etching approach to fabricate n-type gallium nitride (GaN)-based devices without any external power supply. However, the current technology is far from practical because efficient etching can only be realized by a potassium persulfate (PS) oxidant/alkaline electrolyte system that inevitably bends the etching surface. In this study, we proposed and tested a new potassium peroxomonosulfate (PMS) oxidant/weak acid electrolyte system for the photogalvanic etching of platinum (Pt) photo-mask patterned GaN wafers. A novel finding is that Pt can catalyze PMS decomposition in acids, predominantly generating singlet oxygen (1O2), whose onset reduction potential is 0.95 V higher than PS. Under 25.4 mW.cm2 ultraviolet (UV) irradiation, PS-driven photogalvanic etching of inert silicon-doped GaN (si-GaN) wafers is invalid, whereas the new system enables high efficiency and quality etching in 20 mM PMS+0.1 M K2SO4 electrolyte (pH=3.0). The etching rate reaches 12.0 nm.min-1, while the as-prepared groove bottoms have nanometer surface flatness, and the surface roughness (Ra) attains 5.25 nm (5x5 µm2). In summary, the PMS/weak acid electrolyte system makes photogalvanic etching is a promising practical technique.

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