Surface plasmon enhanced responsivity in a waveguided germanium metal-semiconductor-metal photodetector

The authors report on high transverse magnetic (TM)-mode responsivity in a waveguided germanium Schottky-barrier metal-semiconductor-metal photodetector on silicon-on-insulator substrate for operating wavelength at 1550 nm. The employed aluminum interdigitated electrodes act as a one-dimensional rectangular grating above the depletion layer. By means of properly designed finger dimensions, surface plasmon polariton resonances can be excited at the interface of metal and silicon interfacial layer due to grating coupling. The resulting strong field intensities reach into active region, enabling high absorption under TM injection. At a voltage of 1 V, the TM-mode photocurrent is measured over three times than that of transverse electric mode, in spite of the relatively larger TM insertion loss in the silicon waveguide.