Low-temperature growth of GaAs on Si used for ultrafast photoconductive switches
GaAs was grown directly on silicon by molecular beam epitaxy (MBE) at low substrate temperature(∼250°C). Both the silicon wafer cleaning and the GaAs film growth processes were done attemperatures lower than the Si-Al eutectic temperature to enable monolithic integration of low-temperature-GaAs photoconductive switches with finished Si-CMOS circuits. The film surfaces show less than 1 nm rms roughness and the anti-phase domain density is below the detection limit of X-ray diffraction. Metal-semiconductor-metal photoconductive switches were made using this material and were characterized using a time-resolved electrooptic sampling technique. A full-width at half-maximum switching time of ∼2 ps was achieved and the responsivity of switches made from low-temperature GaAs on Si material was comparable to its counterpart on a GaAs substrate.