Antenna-enhanced and polarization sensitive photoresponse in arrays of silicon P–i–N nanowires

Abstract

We analyze a novel antenna effect that resonantly enhances the photocurrent response of end-contacted P–i–N junction nanowire gratings, due to coupling of incident radiation into the grating's multiple-scattering electromagnetic modes. Quantitative characterization of these resonances was performed by spectral and polarization-resolved photocurrent measurements on gratings with N = 500, 200 and 100 nanowires, aided by electron beam-induced current measurements, and in excellent agreement with electromagnetic scattering theory. Despite the small scattering cross-section of each nanowire, with triangular cross-section (height 8 nm, width 6 nm), the measured quality factor of the resonances Q ≈ 10 exceeds that of the empty SiO _2 cavity without degradation for gratings of as few as 100 nanowires. Photoresponse retains sinusoidal polarization anisotropy characteristic of single nanowires. We discuss strategies for improving Q and present a grating design tailoring resonant field enhancement at red, green or blue wavelengths, for three different grating periods of ℓ = 460, 400 and 320 nm.