Tera-hertz GaAs metal-semiconductor-metal photodetectors with nanoscale finger spacing and width

Metal-semiconductor-metal (MSM) photodetectors with nanoscale finger spacing and finger width have been fabricated on MBE (molecular beam epitaxy)-grown GaAs. The smallest finger spacing and width are 25 nm and 15 nm, respectively. Direct dynamic measurement using a femtosecond pulse laser and a 50-GHz sampling oscilloscope showed that the detectors´ speed is much faster than that of the measuring system. Monte Carlo simulations show that, for an MSM photodetector with 25-nm finger spacing, its intrinsic and extrinsic impulse responses are 0.16 ps and 0.25 ps, respectively, and its cut-off frequency is over 1 THz. Finally, the scaling rules in achieving ultra-high-speed MSM photodetectors are discussed.<>