Research on the thermal failure mechanism of an opposed-contact gallium arsenide photoconductive semiconductor switch in avalanche mode

Abstract

The switching mechanism and the thermal process of a gallium arsenide (GaAs) photoconductive semiconductor switch (PCSS) with an opposed-contact is investigated by numerical simulation of the two-dimensional (2D) structure using temperature-dependent physical parameters of the carriers in GaAs. Triggered by a low-energy laser pulse, the PCSS switches on due to the formation and evolution of multiple powerful avalanche domains. The 2D evolving characteristics of the avalanche domains on the two sides of photogenerated plasma during the switching transient are comparatively analysed. It is found that the ionizing centre of each domain moves with the drift of accumulated electrons inside the domain. Meanwhile, the evolution of avalanche domains causes an obvious thermal effect along the drift path of ionizing centres during the switch-on stage of PCSS. Then, the temperature keeps increasing at the edge of the anode and cathode although the switching current starts dropping after the conduction of PCSS, and finally peaks at ∼491 K and ∼541 K, respectively. The simulation results indicate that the 2D filamentary current flows along the drift path of ionizing centres inside the avalanche domains, which finally leads to filamentary erosion after continuous operation of the PCSS. On the basis of numerical simulation, an experiment with opposed-contact GaAs PCSS with 2.5 mm gap at the bias field of ∼90 kV cm−1 is performed. The thermal erosion is found to initially accumulate at the edge of the electrodes and then spreads along the current channel into the GaAs substrate, which is in accordance with the simulation results and analysis.