The Test of a High-Power, Semi-Insulating, Linear-Mode, Vertical 6H-SiC PCSS

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.