Analysis of the Avalanche Operation of a GaN Photoconductive Semiconductor Switch

The operation mechanism of a gallium nitride (GaN) photoconductive semiconductor switch (PCSS) based on a semi-insulating (SI) wafer was analyzed using a physics-based numerical simulation. After the activation of a 532-nm laser pulse with a peak power of 5.3 kW, a 0.1-mm length GaN PCSS biased at 1 kV linearly responded to the excitation laser. When the bias voltage exceeds 2 kV, the GaN PCSS operates in a quasi-avalanche mode. Powerful avalanche domains were numerically observed on the cathode side and then immediately annihilated; these domains could not move across the structure. When the voltage exceeded 4 kV corresponding to a bias field of 400 kV/cm, ultrafast switching occurred due to the evolution of multiple avalanche domains across the structure with a peak field up to several MV/cm. The responsivity of the GaN PCSS in linear mode and the threshold field of avalanche operation with
$\sim $
400 kV/cm showed good agreement with the experimental results in the literature. The physics of multiple powerful avalanche domains with an ultrahigh field was discussed, and these domains were attributed to the negative differential mobility (NDM) of electrons above a critical field value at which the electron velocity reached a maximum. The avalanche operation of the GaN PCSS dependence on the laser power was also investigated.