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Journal of Physics D: Applied Physics - latest papers

Latest articles for Journal of Physics D: Applied Physics

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  • Two-dimensional fluid simulations of sawtooth waveform pulsed inductively coupled Ar/O2 plasma discharges
    In this work, the effect of sawtooth waveforms on the plasma properties in pulsed inductively coupled Ar/O2 discharges is investigated using a two-dimensional fluid model. It is shown that by increasing the slope of sawtooth waveforms with a constant delivery of RF power during the pulse-on phase, the power rises steadily, and the electron density at the beginning of the pulse-on period is higher, which helps to suppress the overshoot phenomenon in the electron temperature. The peak of the potential when the power is turned on also disappears at larger slopes, indicating that the ion bombarding energy on the wafer is lowered. Since the ion flux above the wafer during the first half of the pulse period is the lowest under this condition, the damage to the wafer caused by energetic ion bombardment could be effectively reduced when operating without bias sources. The effects of duty cycle and pulse frequency on the plasma parameters are also investigated, and the results show that increasing the duty cycle is beneficial to suppress the overshoot in the electron temperature and potential, while the influence of pulse frequency is limited.

  • Vertical gallium nitride high-temperature avalanche pin diodes with guard rings structure
    The avalanche capability is essential for high-reliability power electronics devices, but it is difficult to realize avalanche breakdown, which requires high-quality freestanding GaN substrates and sophisticatedly designed edge termination. In this study, the avalanche characteristics of vertical GaN PIN diodes with N-ion implantation guard rings (GRs) were investigated. GaN p–i–n diodes were grown on freestanding GaN substrates by metal–organic chemical vapor deposition. The net carrier concentration in the drift layer is as low as 3.5 × 1015 cm−3 measured by capacitance–voltage (C–V) test. The GRs was formed on the edge of p–i–n diodes via N-ion implantation, resulting in a significant reduction in reverse leakage current density by over 106 times. By optimization of the GRs through a combination of simulations and experiments, we achieved an enhancement in the device’s avalanche breakdown voltage from 759.8 V to 865 V. Notably, the devices maintained an avalanche damage-free breakdown even at an elevated temperature of 225 °C. The relationship between avalanche voltage and temperature is linear, with a positive temperature coefficient of 0.38 V K−1.

  • Parametric amplification of multimode high-kinetic inductance cavity
    Parametric amplifiers have become significant components in qubit readout within circuit quantum electrodynamics. Devices based on high-kinetic inductance (HKI) material can provide an avenue to achieve the considerable gain of parametric amplification. In this work, we develop a parametric amplifier using a multimode HKI coplanar waveguide cavity. We explore two pumping schemes, achieving significant gains for multiple modes in both the monochromatic and bichromatic pump schemes. We first measure parametric amplification in the monochromatic pump scheme, achieving over gain in all modes. In the bichromatic pump scheme, two distinct gain regions emerge in the spectra, accompanied by a triangle-like pattern. Moreover, the bichromatic pump scheme yields a higher gain value than the monochromatic pump scheme, with the maximum gain exceeding . This parametric amplifier holds potential applications, such as frequency-division multiplexing readout, which is beneficial for scaling up qubits in quantum computing.

  • Improving the performance of glow discharge hollow cathode by using low work function materials
    Hollow cathodes are widely used as neutralizers in electric propulsion. Currently, with the trend of satellite miniaturization and diversification of space missions, alternative neutralization technology based on new materials and alternative propellants has become a hot topic. This study compared the discharge characteristics and performance of different cathode materials LaB6 and 304 stainless steel in a direct-current glow discharge hollow cathode (GDHC). Numerical and experimental investigations were conducted on the inner discharge region and outer plume region of the GDHC to analyze the plasma behavior, respectively. Experimental results show that the LaB6 configuration (adding a LaB6 insert into the 304 configuration) can effectively reduce the discharge power cost and improve the gas utilization factor. An anode current of 213.6 mA was achieved at 2 sccm of argon in the LaB6 configuration, corresponding to a discharge power cost of 182 W A−1 and a gas utilization factor of 1.5. The LaB6 configuration exhibits a higher discharge current, resulting in a higher plume plasma density. The simulation results show that the electron density and ion density in the cathode fall (CF) region near the LaB6 insert increase significantly, thereby improving the electron and ion conductivity, and effectively reducing the CF voltage. Comparison reveals that the performance of the GDHC (LaB6) is comparable to RF cathodes and microwave cathodes with argon propellant.

  • Rapid E-FISH measurements using a laser optical loop
    Rapid electric field–induced second harmonic generation measurements are performed using a laser optical loop approach, which facilitates the use of each single laser shot several times. From a single laser shot, E-FISH signals at multiple points in the time domain are generated and recorded as a single waveform. It is also demonstrated experimentally that the polarization-sensitive nature of E-FISH allows to tailor the E-FISH response sensitivity within the pulse train traveling in the optical loop to optimize the measured signal waveform for a given electric field profile while avoiding the saturation of the detector and extending the dynamics range of the measurements.