GaAs Schottky photodiode with 3dB bandwidth of 20 GHz

We have developed and characterized GaAs Schottky barrier photodiodes with 3 dB bandwidths of 20 GHz which corresponds to a Gaussian impulse response with a full width half maximum (FWHM) of 16 picoseconds. These photodiodes, in addition to their wide bandwidths, operate at a reverse bias voltage of less than 5 volts with an associated dark leakage current of 5 picoamperes and still attain external quantum efficiencies of 30% at 600 nm and 25% at 845 nm which translate to a responsivity of 0.15 and 0.17 amperes per watt respectively. The photodiode is a mesa structure with a thin semi-transparent platinum film forming the photosensitive Schottky junction 25 microns in diameter in contact with an offset bond pad. The Schottky junction is formed on a low doped n type GaAs epitaxial layer grown by molecular beam epitaxy on n⁺GaAs substrate. To accurately characterize the transfer function of these high-speed photodiodes to 22 GHz, we have developed a time and freauency domain measurement system.