GaAs photoconductive semiconductor switch fabrication for improved reliability

The reliability of high gain GaAs photoconductive semiconductor switches (PCSS) has been investigated, with the goal of understanding how fabrication parameters impact device lifetime. We aim to produce high-voltage (50–100 kV) PCSS with improved lifetime, or equivalently, since the current in high gain PCSS flows in filaments, increase the current per filament at fixed lifetime. As a simpler model system, a large number of smaller (500 V) switches was tested. These scaled-down switches demonstrate the same failure mechanisms seen in larger switches. The distribution of switch lifetimes is shown to follow a log-normal distribution. Variations in the design and processing of larger switches were studied to ascertain the impact on device lifetime. The lifetime is strongly dependent on switch fabrication process parameters such as the anneal temperature. Design parameters such as the pad metal inset distance and thickness were not found to have the expected improvement in shot life. Evidence points to the surface preparation as a key variable in achieving high shot counts.