Design and Testing of Wide Bandgap Current Limiting Devices

The University of Missouri in collaboration with Helava Systems Inc. have developed a concept and have shown in experiments the feasibility of a solid state switch based on the photoconductive properties of a semiconductor for radar limiters in a linear mode. Three possible device geometries were subsequently designed using CST Microwave Studio (R) which would allow for matched microwave off-state transmission but provide substantial limiting of the signal in the on-state (illuminated) condition. Each design was simulated and the results compared allowing for the best possible geometry to be chosen. The chosen design allowed for greater than 99% off-state transmission and an on-state limiting of less than 1% of the incident signal. Initial experimental tests to determine the semiconductor's effectiveness to act as a photoconductive switch were investigated using highly conductive silver paint. These devices were then subjected to testing and the results compared with simulated calculations in CST and MATLAB (R). Through these tests, the University of Missouri has demonstrated the ability of aluminum gallium nitride (AlGaN) to act as a photoconductive switch when illuminated with 355-nm light. Experiments show a greater than two orders of magnitude drop in semiconductor channel resistance upon illumination. While further investigation into the ability of the device to obtain subohm resistance levels is needed, initial tests and calculations confirm the ability of AlGaN materials to act as a current limiting device with the geometry designed by the University of Missouri.