Fabricating single-crystalline gallium nitride (GaN)-based devices on a Si(100) substrate, which is compatible with the mainstream complementary metal-oxide-semiconductor circuits, is a prerequisite for next-generation high-performance electronics and optoelectronics. However, the direct epitaxy of single-crystalline GaN on a Si(100) substrate remains challenging due to the asymmetric surface domains of Si(100), which can lead to polycrystalline GaN with a two-domain structure. Here, by utilizing singlecrystalline graphene as a buffer layer, the epitaxy of a single-crystalline GaN film on a Si(100) substrate is demonstrated. The in situ treatment of graphene with NH 3 can generate sp 3 CN bonds, which then triggers the nucleation of nitrides. The one-atom-thick single-crystalline graphene provides an in-plane driving force to align all GaN domains to form a single crystal. The nucleation mechanisms and domain evolutions are further clarified by surface science exploration and first-principle calculations. This work lays the foundation for the integration of GaN-based devices into Si-based integrated circuits and also broadens the choice for the epitaxy of nitrides on unconventional amorphous or flexible substrates.

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In this study, Ti3(Al,Ga)C2/Al2O3 composites were successfully synthesized by in situ hot pressing at 1350 °C for 2 h using Ti, Al, TiC, and Ga2O3 as raw materials. X-ray diffraction and scanning electron microscopy were used for characterizing the phase identities and microstructures of the sintered composites. The dependence of the Vickers hardness and flexural strength on the Al2O3 content was found to be in single-peak type. Ti3(Al0.6,Ga0.4)C2/10.3vol%Al2O3 composite exhibited significantly improved mechanical properties. Vickers hardness and flexural strength of the composite reached 6.58 GPa and 527.11 MPa, which were 40% and 74% higher than those of Ti3AlC2, respectively. Formation of solid solution and incorporation of second phase of Al2O3 resulted in the opposite influence on the fracture toughness. Finally, the hardening and strengthening mechanisms were discussed in detail.

We demonstrate that different doping approaches can significantly influence the lattice locations of carbon (C) in GaN grown by MOCVD. For intrinsically doped GaN with TMGa as the C source, an annealing induced switching process of C atoms from Ga sites to N sites is observed, revealing the existence of substitutional C atoms on both Ga and N sites. While for extrinsically doped GaN with propane as the C precursor, C atoms incorporate almost on N sites. From the viewpoint of growth dynamics, we propose a mechanism for C incorporation into different lattice locations.

High quality GaN films on SiC with low thermal boundary resistance (TBR) are achieved by employing an ultrathin low Al content AlGaN buffer layer. Compared with the conventional thick AlN buffer layer, the ultrathin buffer layer can not only improve the crystal quality of the subsequent GaN layer but also reduce the TBR at the GaN/SiC interface simultaneously. The ultrathin AlGaN buffer layer is introduced by performing a pretreatment of the SiC substrate with trimethylaluminum followed by the growth of GaN with an enhanced lateral growth rate. The enhanced lateral growth rate contributes to the formation of basal plane stacking faults (BSFs) in the GaN layer, where the BSFs can significantly reduce the threading dislocation density. We reveal underling mechanisms of reducing TBR and dislocation density by the ultrathin buffer layer. We propose this work is of great importance toward the performance improvement and cost reduction of higher power GaN-on-SiC electronics.

Carbon (C) is of great importance to realize semi-insulating gallium nitride (GaN) for power electronic devices. We demonstrate that C can migrate from Ga sites to N sites after high temperature annealing of C doped GaN. The migration process is revealed through the observation of the generated Ga vacancies-related defects after annealing by positron annihilation spectroscopy. The activation energy of this migration process is estimated to be 2.5–2.8 eV from the temperature dependent annealing experiments, which is well consistent with the theoretical results from first-principles calculations.