Near-infrared photoresponse in Ge/Si quantum dots enhanced by localized surface plasmons supported by aluminum nanodisks

An array of plasmonic nanoparticles can sustain surface plasmon modes from visible to infrared spectral range and thus offers effective surface light trapping, enhancement of local fields, and interaction with the thin active regions of optical devices. We report the fabrication and optical characterization of a planar Ge/Si quantum dot (QD) detector grown on silicon-on-insulator (SOI) substrate for photodetection in the near-infrared telecommunication wavelength range. The multilayer Ge/Si QD heterostructures are near-field coupled to the adjacent layers of aluminum nanodisks on the detector top. The periodic Al disk arrays have the square lattice symmetry with a lattice constant of 400 nm and the disk diameter varying from 150 to 225 nm. A significant enhancement in the room-temperature detector sensitivity is achieved due to the excitation of localized surface plasmons supported by the metallic disks and radiative coupling to the SOI waveguide modes. Through extinction spectroscopy and numerical modeling, we confirm the emergence of nanoparticle-induced plasmon resonances near the Si-Al interface. We demonstrate that an appropriate choice of the array periodicity and the size of the metal disks is able to increase the photodetector's efficiency by similar to 40x at. 1/4 1:2 mu m and by 15x at. similar to 1:55 mu m relative to a bare detector with no plasmonic structure. These outcomes pave the way toward the use of Al as a low-cost plasmonic material with potential applications in infrared photodetection similar to those of the noble metals.