Performance of Lateral 4H-SiC Photoconductive Semiconductor Switches by Extrinsic Backside Trigger

非本征背照触发平面型4H-SiC光导开关性能研究

Photoconductive semiconductor switch(PCSS)can be applied in pulsed high power systems and microwave techniques.However,reducing the damage and increasing the lifetime of silicon carbide(SiC)PCSS are still faced severe challenges.In this study,PCSSs with various structures were prepared on 4-inch diameter,500μm thick high-purity semi-insulating 4H-SiC substrates and their on-state resistance and damage mechanisms were investigated.It was found that the PCSS of an Au/TiW/Ni electrode system annealed at 950℃had a minimum on-state resistance of 6.0Ωat 1 kV bias voltage with a 532 nm and 170 mJ pulsed laser by backside illumination single trigger.The backside illumination single trigger could reduce on-state resistance and alleviate the damage of PCSS compared to the frontside trigger when the diameter of the laser spot was larger than the channel length of PCSS.For the 200 s trigger test by a 10 Hz laser,the black branch-like ablation on Au/TiW/Ni PCSS was mainly caused by thermal stress owing to hot carriers.Replacing metal Ni with boron gallium co-doped zinc oxide(BGZO)thin films annealed at 400℃,black branch-like ablation was alleviated while concentric arc damage was obvious at the anode.The major causes of concentric arc are both pulsed laser diffraction and thermal effect.

光导开关(PCSS)是脉冲高功率系统和微波技术应用中的关键器件,减小碳化硅(SiC)光导开关的损伤,延长器件寿命是重要的研究方向。本工作在直径4英寸、厚度500μm的高纯半绝缘4H-SiC衬底上制备多种结构的光导开关器件,重点研究了导通电阻和损伤机制。1 kV偏压下,采用532 nm、170 mJ的脉冲激光背面照射触发经过950℃退火的Au/TiW/Ni电极体系的碳化硅光导开关,最小导通电阻为6.0Ω。当激光光斑直径大于光导开关器件沟道宽度时,采用背面照射触发相较于前面照射触发可以减小导通电阻并减轻损伤。碳化硅光导开关器件在10 Hz激光下触发200 s,Au/TiW/Ni体系光导开关产生黑色枝状烧蚀损伤,主要原因是热载流子引起的热应力。采用400℃退火的硼镓共掺杂氧化锌(BGZO)薄膜替换金属Ni,黑色烧蚀得到缓解,但是在光导开关阳极出现同心圆弧损伤,其主要成因是脉冲激光的衍射和热效应的共同作用。