Strain modulation is crucial for heteroepitaxy such as GaN on foreign substrates. Here, the epitaxy of strain-relaxed GaN films on graphene/SiC substrates by metal-organic chemical vapor deposition is demonstrated. Graphene was directly prepared on SiC substrates by thermal decomposition. Its pre-treatment with nitrogen-plasma can introduce C–N dangling bonds, which provides nucleation sites for subsequent epitaxial growth. The scanning transmission electron microscopy measurements confirm that part of graphene surface was etched by nitrogen-plasma. We study the growth behavior on different areas of graphene surface after pre-treatment, and propose a growth model to explain the epitaxial growth mechanism of GaN films on graphene. Significantly, graphene is found to be effective to reduce the biaxial stress in GaN films and the strain relaxation improves indium-atom incorporation in InGaN/GaN multiple quantum wells (MQWs) active region, which results in the obvious red-shift of light-emitting wavelength of InGaN/GaN MQWs. This work opens up a new way for the fabrication of GaN-based long wavelength light-emitting diodes.

Solar-light-driven N-doped 3C–SiC powder was synthesized via a simple one-step combustion route. SiC–N₂ photocatalysts exhibited 205.3 μL/(g·h) hydrogen evolution rate, nearly 2 times that of SiC–Ar(120.1 μL/(g·h)), and was much higher than that of SiC nanowires (83.9 μL/(g·h)), SiC nanoparticles (82.8 μL/(g·h)) as well as the B-doped SiC photocatalysts(166 μL/(g·h)). In cyclic tests, N-doped SiC also performed excellent photocatalytic durability and good structural stability. It can be concluded that the influence of N-doping introduced defects into the SiC photocatalyst by occupation and mixed phase structure, transformed the band structure into the direct band gap, and formed a shallow donor level for trapping holes. Consequently, higher photocatalytic activities and lower recombination was achieved. Furthermore, the carbon on the photocatalyst which was yielded from the substitution of N or which remained after combustion would build constructed efficient interfacial contact with SiC for the quickening of light-driven electron transfer to the surface, and simultaneously strengthen the adsorption capacity and light-harvesting potential.

Co-catalyst deposition is used to improve the surface and electrical properties of photocatalysts. In this work, MoS_x/CdIn₂S₄ nanocomposites were prepared by a facile hydrothermal and photodeposition route. The basic crystalline phases and morphology of the as-prepared samples were determined, and these results showed that MoS_x was tightly anchored onto CdIn₂S₄ by sharing the same S atom. In the hydrogen production experiments, MoS_x/CdIn₂S₄-40 displayed the optimal photocatalytic hydrogen production yield in 4 h. The H₂ evolution rate reached 2846.73 μmol/g/h, which was 13.6-times higher than that of pure CdIn₂S₄. Analyzing the photocatalytic enhancement mechanisms revealed that this unique structure had a remarkable photogenerated electron-hole pair separation efficiency, rapid charge carrier transfer channels, and more abundant surface reaction sites. The use of co-catalyst (MoS_x) greatly improved the photocatalytic activity of CdIn₂S₄.

Surface morphologies of triangular defects with TD-I, TD-II and TD-III observed by optical microscopy.

In this study, a novel Al doping method was used to grow p-type SiC. p-Type 4H-SiC crystals were grown by a physical vapor transport (PVT) method using p-type SiC powder.