With the emerging wide bandgap (WBG) semiconductor development, the increasing power density and efficiency of power electronic converters may cause more switching oscillation, electromagnetic interference noise, and additional power loss, further increasing the probability of device failure. Therefore, determining and quantifying the failure of a metal-oxide-semiconductor-field-effect transistor (MOSFET), which assembled using WBG semiconductor in some applications, is crucial to improving the reliability of a power converter. This study proposes a novel failure quantitative assessment approach based on MOSFET parasitic parameters. According to the two-port network theory, MOSFET is equivalent to some second-order RLC circuits composed of independent inductances, capacitances, and resistances in series. Then, the frequency-domain impedance associated with the physical failure of MOSFET is identified through frequency domain reflectometry. Accelerated aging and bond wires cut-off experiments are employed to obtain various quality states of the MOSFET device. Result shows that the MOSFET quality level and its number of bond wire lift-offs can be quantified effectively. Drain-to-source on-resistance (R_DS(on)) that normally represents the MOSFET quality shows a positive linear function relationship on drain-to-source parasitic resistance (R_D + R_S) during the quality degradation proceeding. This finding matches with the correlation established between R_{DS (on)} and R_D + R_S in theory. Meanwhile, source parasitic inductance (L_S) increases with the severity of bond wires faults, and even the slight fault shows a high sensitivity. The proposed approach would be an effective quality screening technology for power semiconductor devices without power on treatment, which can effectively avoid the impact of junction temperature and test conditions (current and voltage) on test results, and does not need to design additional test circuits. The test frequency range we used in this approach was 10–300 MHz, which to some extent is suitable for providing an on-line quality monitoring technology for high-frequency WBG power devices manufacturing.

The mechanical and electronic properties of two GaN crystals, wurtzite and zinc-blende GaN, under various hydrostatic pressures were investigated using first principles calculations. The results show that the lattice constants of the two GaN crystals calculated in this study are close to previous experimental results, and the two GaN crystals are stable under hydrostatic pressures up to 40 GPa. The pressure presents extremely similar trend effect on the volumes of unit cells and average Ga-N bond lengths of the two GaN crystals. The bulk modulus increases while the shear modulus decreases with the increase in pressure, resulting in the significant increase of the ratios of bulk moduli to shear moduli for the two GaN polycrystals. Different with the monotonic changes of bulk and shear moduli, the elastic moduli of the two GaN polycrystals may increase at first and then decrease with increasing pressure. The two GaN crystals are brittle materials at zero pressure, while they may exhibit ductile behaviour under high pressures. Moreover, the increase in pressure raises the elastic anisotropy of GaN crystals, and the anisotropy factors of the two GaN single crystals are quite different. Different with the obvious directional dependences of elastic modulus, shear modulus and Poisson’s ratio of the two GaN single crystals, there is no anisotropy for bulk modulus, especially for that of zinc-blende GaN. Furthermore, the band gaps of GaN crystals increase with increasing pressure, and zinc-blende GaN has a larger pressure coefficient. To further understand the pressure effect on the band gap, the band structure and density of states (DOSs) of GaN crystals were also analysed in this study.

A novel terahertz modulator based on graphene is proposed and designed. The device consists of a silicon ridge covered by a graphene sheet. The transmission properties of the proposed structure demonstrate that the introduction of graphene can improve the switching and filtering performance of modulators, and enhance its field confinement capability. In the case of the number of layers, a blue shift can be observed in the center wavelength with increase of graphene layers. Meanwhile, the relationship between the number of layers and the peak of reflection spectra is an inverse proportion function. In addition, we find that the center wavelength is almost unchanged with respect to the different chemical potential, thus the effective refractive indices of the cross section of light propagation direction can be well preserved. These findings will contribute to the research and development of graphene based THz waveguide modulators.

The sensing properties of pristine, B-, Al-, Si-, and S-doped blue phosphorus (BP) monolayer to nitric oxide (NO) are theoretically investigated using density functional theory and non-equilibrium Green's function method. We systematically discuss the concentration effect, sensing mechanism, and current-voltage (I-V) response of BP adsorbing NO molecule. Our results show that the pristine BP exhibits a weak sensitivity for NO molecule, while B-, Al-, and Si-doped BP strongly adsorb NO via robust chemical bonds, meaning a good potential in metal-free catalysts, but unsuitable as NO sensors. Interestingly, S-doped BP is recommended as a desirable material for NO detection due to moderate adsorption energy and large charge transfer. Besides, the flowing current in S-doped BP can be significantly improved after NO adsorption under the same bias voltage. Therefore, S-doped BP could be a good candidate as an NO sensor.