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€ 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®. 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 sub-ohm 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.