ULTRAFAST RESPONSE OF AS-IMPLANTED GAAS PHOTOCONDUCTORS

The photoconductive response of an optoelectronic switch fabricated fr om 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-impl anted GaAs substrates are determined to be comparable to photoconducti ve devices employing GaAs grown by low-temperature molecular-beam epit axy (LT-GaAs). For high de-bias values, persistent photocurrent tails from transient leakage currents are found to be very prominent in bulk GaAs devices that were implanted with 10(16) cm(-2) arsenic ions at 2 00 keV. This behavior has been determined to arise from substrate leak age current underneath the thin implanted layer, which recrystallizes and exhibits, as does LT-GaAs, arsenic-precipitate formation after ann ealing. 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 i ts semi insulating substrate, and bonded onto a fused silica wafer in order to verify that the persistent tail response from the photoconduc tive switches was not actually due to the implanted region of the GaAs .