The effect of Mg doping on the electrical and optical properties of the p-GaN/AlGaN structures on a Si substrate grown by metal organic chemical vapor deposition was investigated. The Hall measurement showed that the activation efficiency of the sample with a 450 sccm Cp₂Mg flow rate reached a maximum value of 2.22%. No reversion of the hole concentration was observed due to the existence of stress in the designed sample structures. This is attributed to the higher Mg-to-Ga incorporation rate resulting from the restriction of self-compensation under compressive strain. In addition, by using an AlN interlayer (IL) at the interface of p-GaN/AlGaN, the activation rate can be further improved after the doping concentration reaches saturation, and the diffusion of Mg atoms can also be effectively suppressed. A high hole concentration of about 1.3 × 10¹⁸ cm⁻³ can be achieved in the p-GaN/AlN-IL/AlGaN structure.

In this study, we used metal organic chemical vapor deposition to form gallium nitride (GaN) epilayers on c- and a-axis sapphire substrates and then used the nanoscratch technique and atomic force microscopy (AFM) to determine the nanotribological behavior and deformation characteristics of the GaN epilayers, respectively. The AFM morphological studies revealed that pile-up phenomena occurred on both sides of the scratches formed on the GaN epilayers. It is suggested that cracking dominates in the case of GaN epilayers while ploughing during the process of scratching; the appearances of the scratched surfaces were significantly different for the GaN epilayers on the c- and a-axis sapphire substrates. In addition, compared to the c-axis substrate, we obtained higher values of the coefficient of friction (μ) and deeper penetration of the scratches on the GaN a-axis sapphire sample when we set the ramped force at 4,000 μN. This discrepancy suggests that GaN epilayers grown on c-axis sapphire have higher shear resistances than those formed on a-axis sapphire. The occurrence of pile-up events indicates that the generation and motion of individual dislocation, which we measured under the sites of critical brittle transitions of the scratch track, resulted in ductile and/or brittle properties as a result of the deformed and strain-hardened lattice structure.

This work reports molecular beam epitaxy of two-dimensional GaSe_1−xTe_x ternary alloys that have recently attracted a lot of interest in physics and material sciences even though facing crucial challenges in their epitaxial technology.

The AlGaN/AlN/GaN high electron mobility transistor structures were grown on a Si (111) substrate by metalorganic chemical vapor deposition in combination with the insertion of a SiN_x nano-mask into the low-temperature GaN buffer layer. Herein, the impact of SiH₄ flow rate on two-dimensional electron gas (2DEG) properties was comprehensively investigated, where an increase in SiH₄ flow rate resulted in a decrease in edge-type threading dislocation density during coalescence process and an improvement of 2DEG electronic properties. The study also reveals that controlling the SiH₄ flow rate of the SiN_x nano-mask grown at low temperatures in a short time is an effective strategy to overcome the surface desorption issue that causes surface roughness degradation. The highest electron mobility of 1970 cm²/V·s and sheet carrier concentration of 6.42 × 10¹² cm⁻² can be achieved via an optimized SiH₄ flow rate of 50 sccm.

The high electron mobility transistor (HEMT) structures on Si (111) substrates were fabricated with heavily Fe-doped GaN buffer layers by metalorganic chemical vapor deposition (MOCVD). The heavy Fe concentrations employed for the purpose of highly insulating buffer resulted in Fe segregation and 3D island growth, which played the role of a nano-mask. The in situ reflectance measurements revealed a transition from 2D to 3D growth mode during the growth of a heavily Fe-doped GaN:Fe layer. The 3D growth mode of Fe nano-mask can effectively annihilate edge-type threading dislocations and improve transfer properties in the channel layer, and consequently decrease the vertical leakage current by one order of magnitude for the applied voltage of 1000 V. Moreover, the employment of GaN:C film on GaN:Fe buffer can further reduce the buffer leakage-current and effectively suppress Fe diffusion.

Molecular beam epitaxy (MBE) is demonstrated as an excellent growth technique for growing a low-defect GaN channel layer, which is crucial for controlling vertical leakage current and improving breakdown voltage (BV) in GaN-based high-electron mobility transistors (HEMTs). The 3D islands to 2D growth mode transition approach was induced by modulating substrate growth temperature (Tsub), displaying an overall improvement in film quality. A comprehensive investigation was conducted into the effects of Tsub on surface morphologies, crystal quality, and the optical and electrical properties of GaN films. Optimal results were achieved with a strain-relaxed GaN film grown at 690 °C, exhibiting significantly improved surface characteristics (root-mean-square roughness, Rq = 0.3 nm) and impressively reduced edge dislocations. However, the film with the smoothest surface roughness, attributed to the effect of the Ga-rich condition, possessed a high surface pit density, negatively affecting optical and electrical properties. A reduction in defect-related yellow emission further confirmed the enhanced crystalline quality of MBE GaN films. The optimized GaN film demonstrated outstanding electrical properties with a BV of ~1450 V, surpassing that of MOCVD GaN (~1180 V). This research significantly contributes to the advancement of MBE GaN-based high electron mobility transistor (HEMT) applications by ensuring outstanding reliability.