Design and fabrication of ultrafast coplanar strip photoconductive switch based on low-temperature grown GaAs

This paper reports the design and preparation of ultra-fast photoconductive (PC) switch made from a 500 nm thick low temperature grown GaAs (LT-GaAs) on a transparent quartz glass substrate. After the procedures of photolithography, etching, evaporation etc., coplanar strip (CPS) transmission lines of Au/Pt with width and spacing of 10 μm and thickness of 600 nm are evaporated on the substrate of LT-GaAs. The photoconductive switch has ideal dark resistance, good I-V performance and photoelectric linearity under an exposure of weak light. The dark current is about 0.1 pA at a bias voltage of 10 V. The typical risetime of the photoconductive switch is 1.3 ps measured by pump-probe technique with a mode-locked Ti: sapphire laser with pulse width of 100 fs, wavelength of 800 nm, and frequency of 100 MHz.