Study of a Si-based light initiated multi-gate semiconductor switch for high temperatures.

Light initiated multi-gate semiconductor switch (LIMS) is a kind of power electronic device which has many differences from traditional thyristor triggered by electric pulse. LIMS is triggered by laser, the turn-on time is smaller, and the anti-electromagnetic interferences is strong. The opening mode of LIMS is obviously different to traditional thyristor. After the laser into the gate area, a large number of electrons and holes will appear in P-base region, holes gather in the area of P-base in PN junction J2, and electrons gather in N-drift region around the PN junction J2. PN junction J2 will open first, then PN junction J3 opens. The delay time of the NPN and PNP thyristors is close to zero when the laser pulse is narrow and the peak power is high, so the turn-on velocity is fast. To optimize the characteristics of the LIMS at high temperatures, we propose a new structure of the LIMS with the optimization of the n+ layer, circular light gate, and the new-style edge termination. The diameter of the LIMS is 23 mm. The experiment results show that the leakage current of the proposed LIMS has been decreased from more than 1 mA to 500 µA at 125 °C, the output current of the LIMS is 10.2 kA with a voltage of 4 kV at 85 °C, and the output current of the LIMS is 12.1 kA with a voltage of 4 kV at - 55 °C. Additionally, di/dt is larger than 30 kA/µs.

All-solid-state pulsed current injection source based on the light initiated multi-gate semiconductor switches.

To study the damage and protection mechanism of the transient electromagnetic pulse to the cables of the electronic equipment under test, an all-solid-state pulsed current injection source with light initiated multi-gate semiconductor switches is developed. The output peak current range of the prepared all-solid-state pulsed current injection source was 0.1-1 kA, the risetime was 18 ns, and the pulse width was 520 ns. In addition, the waveforms of the output peak current were consistent.

All solid-state electromagnetic pulse simulator based on the 4H-SiC photoconductive semiconductor switch.

To study the damage and protection mechanism of an electromagnetic pulse to an electronic system, an all solid-state high-voltage pulse power with photoconductive semiconductor switch is developed, which is a component of the bounded wave electromagnetic pulse simulator. The output peak voltage of the prepared all solid-state pulsed power source was 74.5 kV, the risetime was 2.05 ns, and the pulse width was 22 ns. In addition, the peak voltage of the output pulse of the all solid-state pulsed power source could be regulated. The all solid-state electromagnetic pulse simulator developed in this work can generate an electromagnetic environment with a risetime of 2.2 ns and a pulse width of 23.5 ns.

Tunable valley splitting and an anomalous valley Hall effect in hole-doped WS2 by proximity coupling with a ferromagnetic MnO2 monolayer.

Two-dimensional (2D) valleytronic systems can provide information storage and processing advantages that complement or surpass those of conventional charge and spin-based semiconductor technologies. For efficient use of the valley degree of freedom, the major challenge currently is to lift the valley degeneracy to achieve valley splitting for further valleytronic operations. In this work, we demonstrate that valley splitting and efficient hole-doping in monolayer WS2 can be achieved by the proximity coupling effect of 2D ferromagnetic MnO2 using density functional theory and Berry curvature calculations. A valley splitting of 43 meV is induced in the valence band of WS2. The efficient hole-doping moves the Fermi level just located between the valence band maxima of the K and K' valleys, which is suitable for the valley-polarized transport. The magnitude of valley splitting relies on the strength of interfacial orbital hybridization and can be tuned continually by applying interfacial compression or an electric field. Owing to the sizable Berry curvature and time-reversal symmetry breaking of WS2, a spin- and valley-polarized anomalous Hall current can be generated. Then, we proposed a valleytronic device that can be used as a filter for both the spin and valley based on this WS2/MnO2 van der Waals heterostructure.

Strain-tunable magnetic anisotropy in two-dimensional Dirac half-metals: nickel trihalides.

The recent discovery of intrinsic two-dimensional (2D) ferromagnetism has sparked intense interest due to the potential applications in spintronics. Magnetic anisotropy energy defines the stability of magnetization in a specific direction with respect to the crystal lattice and is an important parameter for nanoscale applications. In this work, using first-principles calculations we predict that 2D NiX3 (X = Cl, Br, and I) can be a family of intrinsic Dirac half-metals characterized by a band structure with an insulator gap in one spin channel and a Dirac cone in the other. The combination of 100% spin polarization and massless Dirac fermions renders the monolayer NiX3 a superior candidate material for efficient spin injection and high spin mobility. The NiX3 is dynamically and thermodynamically stable up to high temperature and the magnetic moment of about 1 µ B per Ni3+ ion is observed with high Curie temperature and large magnetic anisotropy energy. Moreover, detailed calculations of their energetics, atomic structures, and electronic structures under the influence of a biaxial strain ε have been carried out. The magnetic anisotropy energy also exhibits a strain dependence in monolayer NiX3. The hybridization between Ni d xy and d x 2-y 2 orbitals gives the largest magnetic anisotropy contribution, whether for the off-plane magnetized NiCl3 (NiBr3) or the in-plane magnetized NiI3. The outstanding attributes of monolayer NiX3 will substantially broaden the applicability of 2D magnetism for a wide range of applications.

Effect of Polarization Coulomb Field Scattering on Electrical Properties of the 70-nm Gate-Length AlGaN/GaN HEMTs.

This research presents the first experimental observation of the enhancement of the polarization Coulomb field (PCF) scattering by aggressive lateral scaling of GaN HEMTs. By decreasing the source-drain distance to 300 nm through n+-GaN ohmic regrowth, 70-nm gate AlGaN/GaN HEMTs achieved an extremely low electron mobility. Different from the electron mobility of the traditional device, which was determined by polar optical phonon scattering, the electron mobility of the 70-nm gate AlGaN/GaN HEMTs was dominated by PCF scattering due to the enhanced nonuniform strain distribution of the AlGaN barrier layer. Furthermore, compared with the parasitic access resistance at gate-source voltage VGS = 0 V, the parasitic access resistance at VGS = -2.5 V showed an increase of approximately 700%, which was also responsible for the enhanced PCF scattering.

Effect of Different Gate Lengths on Polarization Coulomb Field Scattering Potential in AlGaN/GaN Heterostructure Field-Effect Transistors.

The AlGaN/GaN heterostructure field-effect transistors with different gate lengths were fabricated. Based on the chosen of the Hamiltonian of the system and the additional polarization charges, two methods to calculate PCF scattering by the scattering theory were presented. By comparing the measured and calculated source-drain resistances, the effect of the different gate lengths on the PCF scattering potential was confirmed.

Influence of the ratio of gate length to drain-to-source distance on the electron mobility in AlGaN/AlN/GaN heterostructure field-effect transistors.

Using measured capacitance-voltage curves with different gate lengths and current-voltage characteristics at low drain-to-source voltage for the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) of different drain-to-source distances, we found that the dominant scattering mechanism in AlGaN/AlN/GaN HFETs is determined by the ratio of gate length to drain-to-source distance. For devices with small ratio (here, less than 1/2), polarization Coulomb field scattering dominates electron mobility. However, for devices with large ratio (here, more than 1/2), longitudinal optical (LO) phonon scattering and interface roughness scattering are dominant. The reason is closely related to polarization Coulomb field scattering.