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

Abstract

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.

Physics and design for 20% and 25% efficiency nanowire array solar cells

“…We assume a terrestrial solar cell at a temperature T = 300 K throughout. Many previous studies have considered a square array of nanowires [19][20][21]. Here, we choose to consider a hexagonal array (Figure 1) since there, the nanowire surface coverage is 15 % higher for given pitch P, which is beneficial for absorption of light if P is fixed between the square and hexagonal array (Supplementary Information Figure S1).…”

“…III-V nanowire arrays show strong diffraction of light, in which case the regular Beer-Lambert law of bulk absorption does not apply [19][20][21][22][23]. Through measurements, it was shown that a nanowire array can absorb almost all the incident light, even if the nanowires cover only 10 % of the surface [24].…”

An Analytic Approach for Optimal Geometrical Design of GaAs Nanowires for Maximal Light Harvesting in Photovoltaic Cells

“…There is a need for fast, accurate modeling tools to enable rapid exploration and optimization of nanowire designs. Conventionally, finite element [4,[9][10][11] and finite difference methods [1,12,13] have been used in optical models of NWSC. While these techniques are highly accurate, they are computationally expensive, limiting their usefulness in a closed-loop global device optimization.…”

Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

“…In fact, enhanced absorptance was studied for optical modes parallel to the NWs axis, exceeding that of planar structures. 195 The refractive index contrast also plays a crucial role in the modal resonance absorption, causing the optical absorption to be higher than thin film structures. 196 Moreover, NW photodetectors showed superior sensitivity compared with the planar devices, due to the high surface-to-volume ratio that leads to larger photoconductive gain.…”