Wavelength-selective absorptance in GaAs, InP and InAs nanowire arrays.

The absorptance in vertical nanowire (nw) arrays is a result of three optical phenomena: radial mode resonances, near-field evanescent wave coupling, and Fabry-Perot (F-P) modes. The contribution of these optical phenomena to GaAs, InP and InAs nw absorptance was simulated using the finite element method. The study compared the absorptance between finite and semi-infinite nw lengths with varying geometrical parameters, including the nw diameter, length and array period. Simulation results showed that the resonance peak wavelength of the HE11 and HE12 radial modes linearly red-shifted with increasing nw diameter. The absorptance and spectral width of the resonance peaks increased as the nw length increased, with an absorptance plateau for very long nws that depended on diameter and period. Near-field coupling between neighboring nws was observed to increase with decreasing period. The effect of F-P modes was more pronounced for shorter nws, with a significant enhancement of HE12 over HE11 absorptance. Engineering of nw arrays to take advantage of these optical phenomena for multi-spectral photodetector applications is discussed.