GaAs thin films grown at 200 to 250 °C exhibit excellent resistivity and subpicosecond relaxation times of photogenerated carriers, making them attractive materials for ultrafast photodetectors. But practical integration of film structures into electronic circuits first requires them to be fabricated on a microscopic scale.Collaborators at Research Center Jülich in Germany and the University of Rochester in New York described such a method in the Oct. 28 issue of Applied Physics Letters. They used photolithography and ion-beam etching to pattern a set of low-temperature-grown GaAs microswitches that measure from 10 x 10 µm to 150 x 150 µm. The switches were transferred into microwells in either sapphire or Si/SiO2 substrates and integrated with coplanar transmission lines to form freestanding photoconductive microswitches. The devices demonstrated 0.55-ps-wide responses under 810-nm excitation by femtosecond-pulsed laser, and 1.35-ps-wide responses at 405 nm. Photoresponse amplitudes reached 1.3 V, and responsivity topped 1000 V/W.