The electronic structures and effective masses of the N mono-doped and Al-N, Ga-N, In-N codoped ZnO system have been calculated by a first-principle method, and comparisons among different doping cases are made. According to the results, the impurity states in the codoping cases are more delocalised compared to the N mono-doping case, which means a better conductive behaviour can be obtained by codoping. Besides, compared to the Al-N and Ga-N codoping cases, the hole effective mass of In-N codoped system is much smaller, indicating the p-type conductivity can be more enhanced by In-N codoping.

The response of the mechanisms of the α polymorph of CL-20 (α-CL-20) to high temperature is important for understanding the phenomenon of shock initiation, shock ignition, and detonation. The thermal decomposition of α-CL-20 hydrate and pure α-CL-20 were studied by ReaxFF reactive molecular dynamics simulations to obtain the time evolution of water molecules and the effect of H2O on the mechanisms of CL-20 at high temperatures. It was determined that the initial decomposition mechanisms of CL-20 are not dependent on the presence of water, but the secondary reaction pathways are. At low temperatures (T<1500 K), there is no relationship between the H2O, hydrate CL-20, and pure CL-20 systems, as the mechanism is only the dissociation of the N-NO2 bond to form the NO2 radical. At high temperatures (1500 K≤T≤2500 K), water molecules act as a reactant or form catalytic systems with NO2 radical to form OH radical, leading to the formation of O2, H2O2, and other products. Water molecules accelerate the secondary stage reaction of hydrate systems, leading to increased secondary reaction rates and number of NO2 radicals in the CL-20 hydrate compared with the pure CL-20 system. At very high temperatures (T>2500 K), the dissociation of water molecules competes with the initial thermal decomposition pathway of CL-20, leading to a larger rate constant for the pure CL-20 than for the hydrate CL-20.

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As reported by several market analysts, GaN-based power devices show great potential applications in the low and medium voltage range ( < 900 V). For high voltage ( > 1200 V), including ship transportation and power grid, the future applications of GaN highly depend on the development of vertical devices based on GaN substrates. Several vertical devices have been reported, such as current aperture vertical electron transistors (CAVETs), U-shape trench metal-oxide-semiconductor field-effect transistors (UMOSFETs), and fin power transistors. And the UMOSFETs show potential advantages due to greater simplicity in material epitaxy and fabrication process. In the fabrication of UMOSFETs, the U-shape trench dry etching is the most critical process. The GaN sidewalls after dry etching directly affect the interface state characteristics in the MOS structure and the channel electron transport. In this work, etching optimization including etching radio-frequency (RF) power and etching mask is investigated and process-dependent electrical characteristics of GaN UMOSFETs are also studied. The appropriate decrease of RF power ensuring the steep sidewalls can effectively improve the channel electron mobility from 35.7 cm²/(V·s) to 48.1 cm²/(V·s) and consequently increase the ON-state current and reduce the ON-state resistance. Larger etching damage to the p-GaN sidewall caused by higher RF power leads the scattering effects to increase and the mobility of the channel carriers to decrease. The interface state density at the channel can be extracted by the subthreshold swing. The interface state density decreases to 1.90 × 10¹² cm^–²·eV^–1 when the RF power is regulated to 50 W, which is only half of the interface state density when RF power is 135 W. Similar breakdown voltages (350－380 V) are measured for these devices with varying RF power, which are governed by gate early breakdown. Positive valence band offset is formed in the SiO₂/GaN MOS structure and the early breakdown occurs due to the holes accumulating at the SiO₂/GaN interface. The etching uniformity at the bottom of U-shape trench can be improved by using the SiO₂ hard masks instead of photoresist masks. Sub-trenches at both ends of the trench bottom are observed in the device with photoresist masks, leading the carrier scattering to increase and ON-state current to decrease. Besides, the interface state density decreases from 3.42 × 10¹² cm^–2·eV^–1 to 2.46 × 10¹² cm^–2·eV^–1 with a SiO₂ hard mask layer used. Compared with 1.6 μm photoresist mask, the thinner SiO₂ mask with a thickness of 500 nm has a small sidewall area, which weakens the high-energy ion reflection in the inductively coupled plasma system. Consequently, the over-etching at the bottom ends of the trench is improved significantly and therefore the fabricated GaN UMOSFET has higher channel mobility and a lower interface state density.

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