High harmonic generation in crystalline silicon irradiated by an intense ultrashort laser pulse

We investigate the high harmonic generation in bulk silicon irradiated by intense near-infrared laser pulses with pulse duration $$\le $$ ≤ 100 fs. For peak field strength of the applied laser is below 1 V/Å, the spectral intensity of the emitted harmonics follows the prediction of perturbative nonlinear optics—the frequency comb consists of a series of discrete peaks at odd harmonic orders. For a pulse duration longer than 30 fs and peak laser field strength exceeding 1 V/Å, non-perturbative effects and generation of even order harmonics occur. The appearance of even harmonics is due to optical rectification of the transmitted pulse, which includes weak quasi-DC component with electric field as low as 3 V/$$\upmu $$ μ m. In the strong coupling regime, when the peak field strength inside vacuum exceeds 1.5 V/Å, the laser creates dense breakdown plasma of electron–hole pairs, which in turn results in severe spectral broadening of the transmitted pulse. The harmonic spectrum superimposes onto a continuous background, the spectral width of individual harmonics is substantially broadened, and their central wavelength undergoes a blue shift that covers the spacing between adjacent harmonic orders. Graphic abstract

Flashover and Surface Charge in GIL Insulator

Many works have been studies in order to improve flashover voltage in GIL insulator. Under DC, the insulator electric field is decided by the conductivity and surface charge distribution. This chapter takes cone-type insulator as research object and then finds the characteristics of flashover, surface charge accumulation, and the interface electric field regulation (IER) of epoxy (EP)-/graphene (GR)-coated insulator. Theoretical analysis demonstrates that the uniform surface charge of monopole is conducive by reduce peak field and flashover voltage. Among them, that of 0.1% EP/GR possesses the highest flashover voltage. With the SiC content and coating thickness enhancement of IER insulator, the electric field regulation of EP/SiC-coated insulator becomes notable, due to energy loss and increasing leakage current. The results show that insulator coated by EP/SiC can reach higher flashover voltage than uncoated insulator and enhanced SiC content contributes to improve the flashover voltage.

Design and fabrication of a power Si/SiC LDMOSFET for high temperature applications

Power Si/SiC LDMOSFET are being developed for the benefits of high temperature space and terrestrial harsh-environment applications. For the first time, high voltage devices are fabricated on a direct bonded Si/SiC substrate and characterised at room temperature. Peak field-effect channel mobility of the fabricated MOSFET reached ≈300 cm2/V.s and the avalanche breakdown was not observed up to 200 V, despite of a high leakage current in the device off-mode.

Improved 4H-SiC N-MOSFET Interface Passivation by Combining N2O Oxidation with Boron Diffusion

A new oxide configuration for the development of high mobility 4H-SiC lateral MOSFETs is proposed in this work. The oxide is composed by a rapid thermal oxidation (RTO) in N2O environment, a Boron diffusion into the SiO2 and a PECVD TEOS deposited oxide, in order to improve the interface quality. The obtained MOSFETs show very high peak field effect mobilities ranging from 80 up to more than 170 cm2V-1s-1 in MOSFETs with higher channel length than the tested transistors. The physical (SIMS) and electrical analysis of the oxide and SiC surface reveals that the Boron has not diffused into the SiC. This is most probably due to the high concentration of Nitrogen at the interface generated during the N2O oxidation.

Combined N2O and Phosphorus Passivations for the 4H-SiC/SiO2 Interface with Oxide Grown at 1400°C

Phosphorus (P) passivation is more effective than N2O passivation in improving the 4H-SiC/ SiO2 interface by reducing the number of traps at the 4H-SiC/SiO2 interface. This paper investigated the effect of combined N2O and phosphorus POA on the 4H-SiC/SiO2 interface with oxides grown at 1400°C and used in the fabrication of MOS capacitors and FETs. These fabricated devices are also compared with the ones which have been N2O and P passivations only. Results demonstrated that the phosphorus passivation technique provides the highest peak field-effect mobility for 4H-SiC MOSFETs (60 cm2/V.s), which is about 5 times higher than the value obtained for devices with N2O annealing. The combined N2O and phosphorus passivation technique, however, has shown a slight decrease in the peak field effect mobility value compared to the phosphorus passivation technique, but it is still much higher than the N2O passivation technique (12 cm2/V.s).

Particle trajectories in Weibel magnetic filaments with a flow-aligned magnetic field

For a Weibel shock to form, two plasma shells have to collide and trigger the Weibel instability. At saturation, this instability generates magnetic filaments in the overlapping region with peak field $B_{f}$. In the absence of an external guiding magnetic field, these filaments can block the incoming flow, initiating the shock formation, if their size is larger than the Larmor radius of the incoming particles in the peak field. Here we show that this result still holds in the presence of an external magnetic field $B_{0}$, provided it is not too high. Yet, for $B_{0}\gtrsim B_{f}/2$, the filaments become unable to stop any particle, regardless of its initial velocity.

A sensitivity analysis on the electron transport within zinc oxide and its device implications

ABSTRACTZinc oxide has recently been touted as a material that may prove useful for high-power and high-frequency electron device applications. Unfortunately, at the present moment at least, zinc oxide’s electron transport results are based upon material parameter selections that remain disputed, i.e., their exact values have yet to be satisfactorily resolved. In order to establish how the expected range of disputed material parameter values influence the corresponding electron transport results, this paper assesses the sensitivity of the electron transport results associated with zinc oxide to variations in these disputed material parameters. The disputed material parameters that we focus on for the purposes of this particular analysis include the non-parabolicity coefficient associated with the lowest energy conduction band valley, the conduction band inter-valley energy separation, and the effective mass associated with the electrons in the upper energy conduction band valleys. For the purposes of this analysis, steady-state electron transport results are the focus of this sensitivity analysis, the velocity-field characteristic associated with zinc oxide being the principal metric of concern. We find that increases in the non-parabolicity coefficient associated with the lowest energy conduction band valley lead to increases in the peak field of the velocity-field characteristic and initially an increase and then a decrease in the peak electron drift velocity of this material. Increases in the conduction band inter-valley energy separation are instead found to result in increases in the peak field and concomitant increases in the peak electron drift velocity. Finally, increases in the effective mass associated with the electrons in the upper energy conduction band valleys are found to lead to a sharpening of the slope of the velocity-field characteristic in the region beyond the peak field, greater effective mass leading to a greater magnitude slope. Based on the magnitude of these variations, we conclude that zinc oxide may indeed be considered as a material for high-power and high-frequency electron device applications even when the variations in these disputed material parameters have been accounted for.

Characterization of Interface State Density from Subthreshold Slope of MOSFETs at Low Temperatures (≥ 10 K)

We have evaluated interface state density (DIT) for EC−ET > 0.00 eV from the subthreshold slope deterioration of MOSFETs at low temperatures. We have compared two n-channel MOSFETs on the C- and a-faces with the gate oxide formed by pyrogenic oxidation followed by annealing in H2. The peak field-effect mobility (µFE,peak) for the C-face MOSFET was 57 cm2V-1s-1 at 300 K, which is lower than the half of 135 cm2V-1s-1 for the a-face MOSFET. We have shown that DIT very close to EC can well explain why µFE for C-face MOSFETs is lower than that for a-face MOSFETs. The value of DIT at 0.00 eV corresponding to the subthreshold slope at 11 K was 1.6×1014 cm-2eV-1 for the C-face MOSFET, which is more than the double of 6.4×1013 cm-2eV-1 for the a-face MOSFET.