Ultrafast response of As-implanted GaAs photoconductors

The photoconductive response of an optoelectronic switch fabricated from GaAs implanted with arsenic ions is measured to have a duration as short as 0.7 ps and a relaxation time as fast as 0.5 ps. The switching efficiency and relaxation time of the photoswitches using the As-implanted GaAs substrates are determined to be comparable to photoconductive devices employing GaAs grown by low-temperature molecular-beam epitaxy (LT-GaAs). For high dc-bias values, persistent photocurrent tails from transient leakage currents are found to be very prominent in bulk GaAs devices that were implanted with 10¹⁶ cm^-2 arsenic ions at 200 keV. This behavior has been determined to arise from substrate leakage current underneath the thin implanted layer, which recrystallizes and exhibits, as does LT-GaAs, arsenic-precipitate formation after annealing. In order to reduce this leakage current, multiple ion dosages with various implantation energies have been implemented. An epitaxial GaAs layer has also been implanted with arsenic ions, isolated from its semi-insulating substrate, and bonded onto a fused silica wafer in order to verify that the persistent tail response from the photoconductive switches was not actually due to the implanted region of the GaAs