Enhanced Photoresponsivity of a Germanium Single-Nanowire Photodetector Confined within a Superwavelength Metallic Slit

Single nanowire photodetectors (SNPDs) have recently gained much attention due to their unique photonic and electronic properties. We design a germanium SNPD confined inside a silver slit and demonstrate that properly engineering the slit into superwavelength scale is able to dramatically enhance the SNPD photoresponsivity to transverse electric incidence. The light absorption by this rationally designed device can be over 3.7 times that of its subwavelength counterpart based on plasmonic resonance under transverse magnetic incidence. An extensive investigation on polarization dependence, field profile, photon flux distribution, and azimuthal absorption pattern in the SNPD reveals that the underlying mechanism responsible for the significant performance enhancement is the optimal light-nanowire coupling, benefiting from strong interference-directed light concentration inside the slit cavity. This work provides us new insights, beyond the mostly studied plasmonic enhancement effects, into photoresponsivity optimization of SNPDs.