Vertical silicon metal–semiconductor–metal photodetectors with buried CoSi2 contact

Abstract

We report on design, fabrication, and characterization of an ultrafast vertical metal–semiconductor–metal photodetector. A CoSi2 layer in silicon acts both as a bottom Schottky contact and a buried light reflector. A semi-transparent metallization on top of a photosensitive silicon mesa serves as top Schottky contact. Time-domain studies of the pulse response are performed by electro-optic sampling measurements on photodetectors integrated monolithically into microstrip transmission lines. At room temperature, carrier sweep-out is dominated by hopping transport involving shallow traps. At low temperatures, hopping transport is strongly suppressed. As a consequence, the speed of the diode is considerably enhanced, reaching a pulse response with a full width at half maximum of 6.5 ps.