Fabrication and subpicosecond optical response of low-temperature-grown GaAs freestanding photoconductive devices

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Abstract
We have fabricated and tested freestanding low-temperature-grown GaAs photoconducting devices exhibiting subpicosecond photoresponse. The epitaxially grownthin-filmmicroswitches were transferred on top of sapphire and Si/SiO 2 substrates and integrated with Ti/Au coplanar strip transmission lines. Our devices exhibited above 200 V breakdown voltages and dark currents at 100 V below 3×10 −7 A. The photoresponse of our microswitches was measured using electro-optic sampling technique with 100-fs-wide laser pulses at wavelengths of 810 nm and 405 nm as the excitation sources. For 810-nm excitation, we measured 0.55-ps-wide electrical transients with voltage amplitudes of up to 1.3 V. The ultraviolet excitation resulted in 1.35-ps-wide transients due to the hot carriers generation and intraband relaxation.