Fast GaAs Photoconductive Detectors with High Sensitivity Integrated in Coplanar Systems onto GaAs Substrates

Since its introduction in 1975 /1,2/, high-speed sampling of voltage transients on transmission lines using photoconductive switches has been of great interest. Besides superior equivalent bandwidth, it offers a dynamic range considerably larger than conventional sampling oscilloscopes, and complete isolation between the transmission line under test and the sampling circuit. Despite these advantages, it has never found widespread use outside the research area, mainly due to the costly ps dye lasers required. A sampling system using a semiconductor laser would resolve this problem, provided it has a temporal resolution equal or superior to conventional sampling oscilloscopes (≤25 ps). Besides the generation of ps pulses with semiconductor lasers /3/, which will not be discussed here, a photoconductive gate with a carrier lifetime ≤10 ps is necessary, yet sensitive enough to efficiently sample when controlled by pJ pulses from a laser diode.