Ultrafast long-wavelength photodetectors fabricated onlow-temperature InGaAs on GaAs

The authors report the first successful demonstration of a metal-semiconductor-metal photodetector (MSMPD) fabricated on low-temperature InGaAs grown on GaAs by molecular beam epitaxy (MBE) for long-wavelength fiber optic applications. Interdigitated MSMPDs with finger widths and spacings of 0.2, 0.5, 1.0, and 2.0 μm were tested using a femtosecond pulsed laser and high-speed electrooptic sampling. A FWHM pulsed response of 2 and 1.3 ps was measured for low-temperature In _0.25Ga_0.75As and In_0.35Ga_0.65As, respectively. The latter is the fastest response reported to data for a photodetector capable of detection to wavelengths as long as 1.3 μm