Filamentary electrical breakdown in photoconductive GaAs-switches

Summary form only given. The temperature and electric field induced shift of the absorption edge in semiconductors has been used to study the temporal development of the electrical breakdown in a high-power photoconductive GaAs switch. The spatial distribution of the transmission of the probe laser light, with wavelength tuned to the band edge of GaAs, is recorded with a CCD (charge coupled device) camera. Depending on the applied voltage, the temporal development of the switch current shows two distinctively different patterns. At low voltage the photocurrent scales linearly with the activating laser intensity (linear mode). Above a threshold voltage which is dependent on laser intensity, the photocurrent continues to flow as long as a voltage is applied even after the laser is turned off (lock-on mode). This "permanent photocurrent" is carried by one or more luminous filaments. The filamentary breakdown is preceded by the development of domain-like field structures in the anode region of the switch immediately after laser activation. The electric fields in the domains exceed values of 15 kV/cm. The current filament shortens these high field regions and heats the material along its path, causing irreparable changes in the switch material.