A high-power photoconductive semiconductor switch (PCSS) working in linear mode can be used for RF generation by modulating the illuminating light. Such a PCSS constructed of a semi-insulating 6H silicon carbide (6H-SiC) substrate and its characterization under a high electric field is presented. The PCSS is of a vertical structure, with one hollow/transparent electrode to let through the laser light and the other highly reflective to increase light absorption. First, to optimize the high-voltage withstanding, the factors affecting the field enhancement, such as substrate thickness, electrode profiles, and encapsulating materials, are discussed. Then, the PCSS is assembled and tested, and the 0.8-mm-thick 6H-SiC PCSS is able to work with electric fields up to 225 kV/cm and the power capacity up to 10.6 MW without failure when triggered by a Nd:YAG laser (532-nm, 17-ns full wavelength at half maximum). By varying the optical energy from 3 to 31.9 mJ, the minimum conducting resistance and the peak photocurrent of the PCSS are obtained. The PCSS fails with further increasing voltage, and the cause of the failure was identified to be a bulk breakdown. The result shows that the PCSS can work linearly and it is possible to be used in high-power compact RF generation.

In this article, an ultrahigh repetition frequency sub-nanosecond pulse generator based on vanadium-compensated semi-insulating (VCSI) 4H-SiC photoconductive semiconductor switch (PCSS) under high bias electric field is presented. In this work, the 0.8 mm-thick 4H-SiC PCSS was found to work with electric fields up to 200 kV/cm and power capacity of 176 kW. The VCSI 4H-SiC PCSS response test was performed with a 1 MHz, 1030 nm laser cluster driver with configurable optical pulsewidth and current viewing resistor (CVR) high frequency response circuit. In the experiment, the laser pulsewidth was varied between 300 and 500 ps, and 1.5 ns. The system generated a 1 MHz repetition frequency pulse with a minimum half-width of 365 ps and less than 100 ps of jitter. The results revealed higher response performance for single/continuous pulse triggered light of various pulsewidths. Due to the low absorption efficiency of 4H-SiC for non-intrinsic light, an axial optical reflection trap structure was utilized to boost the light absorption efficiency of PCSS. The proposed structure significantly improved the light absorption performance of PCSS devices. The photocurrent increase ratio of roughly 115% was obtained. This study presents the first results of MHz re-frequency high-power switching in bulk semi-insulating 4H-SiC.

A frequency-agile microwave generating system is examined in this letter. Vanadium-compensated semi-insulation (VCSI) 4H-SiC photoconductive semi- conductor switch (PCSS) has been introduced to achieve wide-range frequency tuning. The output microwave frequency is tuned by adjusting the pulse width of the laser. Both the simulation and the experimental results show a tuning frequency range of 0.5 GHz to 10.0 GHz. The maximum operating output power of the system at 10 GHz is 1.13 W, equivalent to a charging voltage of 1.5 kV and a modulated light wavelength of 1064 nm. Further experiment revealed that with 355 nm laser and charging voltage of 5 kV, the output power could be increased to 86.5 kW.

High-power photoconductive semiconductor switch (PCSS) working in linear mode can be used for RF generation by modulating the illuminating light. This paper presents a design and initial test of an optoelectronic class B push-pull microwave power amplifier (MPA) using two 6H-SiC photoconductive switches. The initial tests have been conducted with bias voltage of ±2.4 kV, at 80 kW peak laser pulse power, demonstrating that the SiC PCSS working in linear mode can produce microwaves. Then circuit simulation is conducted to study the factors affecting the electrical efficiency, such as the quantum efficiency, the peak laser pulse power and the bias voltage. It is speculated that the MPA could output 1 MW microwave power and achieve electrical efficiency of more than 60% with a bias voltage of 15 kV, quantum efficiency of 0.2 and peak laser pulse power of 100 kW.

Velocity saturation characteristics of a V-doped 6H silicon-carbide (SiC) photoconductive switch under high electric field are presented. A vertical-geometry switch device based on vanadium-compensated silicon carbide is triggered by a 532-nm laser pulse with light peak-power of several hundred kW and operational voltages from 2 to 20 kV. The maximum electrical peak-power achieved by the device is up to 1 MW (~50 A, 20 kV, 1.1 ns pulse width). When the working voltage is increased to increase output power, the carrier-velocity saturation under high electric field unavoidably impedes the current growth and directly limits the peak power. The parameters of parallel high-field-dependent mobility are obtained with different fields and laser energies: low-field mobility μ = 227 cm2/V s and fitting parameter β = 1.7. With working voltage increasing steadily, a crack-forming process results in device degradation as a result of large current and high electric field. The IV characteristic curves of the simulations and tests show current saturation and possible damage under high electric field.

Magnetic pulse compressors, based on magnetic switches, are considered as competitive candidates for high-voltage pulse generation. In this paper, an adjustable high power magnetic pulse compressor, which is deemed as the key component of a power supply system, is investigated theoretically and experimentally. Dominant parameters of the compressor, including compression ratio, saturation time, and peak voltage, can be regulated, which is beneficial for widening the application areas of power supply systems. Specifically, the pre-pulse of the magnetic pulse compressor is studied as one of the key parameters. A two-stage magnetic pulse compressor was then setup. When the charging time was alternated between 19 μs and 25 μs, pulses with rise-time of 1 μs were achieved with good repeatability. The compressor successfully enabled the generation of intense electron-beam with peak power over 5 GW, peak voltage of 380 kV. The device has been successfully used for research on plasma science and driving high power microwave sources. Based on the high reliability of the pulse generator, optical diagnosis has been conducted of the plasma expansion characteristics of the magnetically insulated coaxial diodes cathode, in order to analysis the mechanism of the pulse shortening phenomenon. Experimental results show reasonable agreements with the analyses.