Photoconductive switch using epitaxial lift-off low-temperature-grown GaAs

In this paper we introduce an ultrafast photoconductive (PC) switch made from low-temperature-grown GaAs, which was fabricated for the generation and detection of electric transients in an ultrafast scanning tunneling microscope (USTM) system. The PC switch was manufactured on a quartz glass substrate. This transparent substrate allows illumination ranging from the front side to the backside. The use of quartz glass as the substrate enables also the low loss of the transmission of frequencies up to the THz regime. A coplanar strip line (CPS) was integrated on the PC switch, in order to propagate THz pulse on the transmission line. For a CPS with width and spacing of 10 μm and the PC switch with width of 50 μm, the dark current between the two electrodes is about 0.1 pA with a switch voltage at 10 V. The obtained PC switch showed linear I-P, I-V characteristics, low noise, high sensitivity, low dark current, and low background current. The USTM measurements show also a full width at half maximum (FWHM) pulse width of 1.3 ps.