Structural Design Of Wide Band Gap Photoconductive Power Switch

The dark-state leakage current problem of a semi-insulated GaN photoconductive semiconductor switch(PCSS)with a traditional PCSS structure,limits the high-voltage superiority of wide bandgap semiconductor material.Therefore,in this paper a reasonable classification method on PCSS structures is proposed for comparing their advantages and disadvantages,and then a novel gate-controlled PCSS is presented-P-gate AlGaN/GaN-PCSS.This novel structure is of the vertical device and is considered to be composed of two parts based on triggering mechanism:an electric-triggered area and a laser-triggered area.The main feature of the structure is that,a reverse pn-junction is formed in homogeneous epitaxies on the semi-insulated GaN substrate for restraining the dark-state leakage current,a heteroepitaxy AlGaN/GaN is made for generating a two-dimensional electron gas(2DEG)layer,and then a P-gate is made for controlling the on-off of the 2DEG layer and the reverse pn junction.The P-gate AlGaN/GaN-PCSS structure is easier to be realized in semiconductor process comparing with an U-shaped groove insulated-gate PCSS structure model and a double-diffused insulated-gate PCSS structure model,since the structure is based on a P-gate AlGaN/GaN HEMT cell array to control of the reverse pn junction and the conduction channel in the electric-triggered area.In addition,the turn-on speed and the repetition-frequency of the structure is better than the latter two structures,since the former operates with the 2DEG but not with the channel generated in an inversion layer.In this paper,a physical device model of P-gate AlGaN/GaN-PCSS is established,and the static and the dynamic characteristics of the device are simulated,respectively.The simulation results show that:1)the withstand voltage of the electric-triggered area is approximately a constant if reasonably setting the concentration and the thickness of the epitaxial layers on the reverse pn-junction;2)when a bias voltage is greater than the voltage constant,the bias voltage is shared between the electric-triggered area and the laser-triggered area;3)the device with a thickness of 518 μm is able to withstand a bias voltage of 10 kV through parameter optimization;4)giving a gate signal greater than the gate threshold voltage,the electric-triggered area is quickly turned on,the voltage of the electric-triggered area can be transiently transferred to the laser-triggered area,and then the device outputs an ultra-fast photocurrent pulse when an ultra-short pulsed power laser illuminating the laser-triggered area;5)compared with the simulation of a relevant traditional vertical PCSS structure,the P-gate AlGaN/GaN-PCSS can effectively suppress the high-voltage dark-state leakage current and the thermal collapse of the device,and can improve the photoelectric conversion efficiency of the device to a certain extent.