High Voltage GaN Lateral Photoconductive Semiconductor Switches

High voltage (>4000 V) GaN lateral photoconductive semiconductor switches (PCSSs) were developed and characterized. The epitaxial structure consisted of 1.4 μm of semi-insulating GaN grown on a SiC substrate. Intrinsic mode operation, where above bandgap light is used to trigger the PCSS, results in the highest amount of photocurrent. These PCSSs can also be triggered in extrinsic mode, where sub-bandgap illumination excites carriers from extrinsic defect levels, but this results in a significantly lower photocurrent. Triggering at near bandgap with 10 V applied, the on-state photocurrent is over eight magnitudes higher than the dark off-state leakage, indicating extremely high responsivity. A 293 nm picosecond pulse width laser was used to determine the rise time of the PCSS to be ∼160 ps. Various geometry devices were fabricated, and the low voltage on-state current obeyed a linear trend as a function of perimeter/gap optically while optically gating the PCSS, which is analogous to the width/length of a metal oxide semiconductor field effect transistor. Off-state breakdown voltages >4000 V were achieved and were likely limited by the thickness of the GaN epitaxial layer.