Plasmon-Enhanced Light Absorption in GaAs Nanowire Solar Cells: A Finite‑Difference Time‑Domain Study

Abstract

We present a finite‑difference time‑domain (FDTD) investigation of vertically aligned GaAs nanowire (NW) arrays functionalized with Au nanoparticles (NPs). The NWs, 1 µm long with 100 nm diameter and 165–500 nm periodicity, are decorated with 30–60 nm Au NPs on their sidewalls. Our simulations reveal that plasmonic resonances of the Au NPs markedly enhance absorption near the GaAs band‑edge, delivering up to a 35 % increase at 800 nm. This enhancement translates into higher electron–hole generation and a measurable boost in overall solar‑cell efficiency, demonstrating the promise of this hybrid architecture for next‑generation photovoltaics.

Introduction

Renewable energy demands have accelerated research into thin‑film photovoltaics, yet material defects and limited absorption constrain their performance. Emerging nanostructures—especially III–V semiconductor nanowires—offer high absorption coefficients, direct bandgaps, and superior charge‑carrier mobilities, making them attractive for low‑cost, high‑efficiency cells. When coupled with plasmonic metal nanoparticles, these nanowires can trap light more effectively, enhancing photocurrent in photodiodes, photodetectors, and solar‑cell architectures. While numerous studies have explored plasmonic enhancement in planar cells, investigations on plasmon‑assisted III–V nanowire arrays remain sparse. Here, we use FDTD simulations to quantify how Au NPs improve the optical response of p‑i‑n GaAs nanowire solar cells, offering a practical design route toward high‑efficiency devices.

Materials and Methods

Figure 1a,b illustrate the unit cell of our proposed device: a periodic array of p‑i‑n GaAs nanowires (D = 100 nm, L = 1 µm, P = 100–500 nm) decorated with 30–60 nm Au NPs on the sidewalls. The nanowires are embedded in a GaAs substrate. Periodic boundary conditions in the x–y plane enforce the lattice periodicity, while perfectly matched layers cap the top and bottom of the simulation domain. A plane‑wave source with AM1.5G spectrum (300–1000 nm) impinges along the z‑axis, and reflection/transmission monitors record the optical response. Material parameters—mobility, SRH lifetime, effective density of states, Auger coefficient, surface recombination velocity—were taken from recent literature. Optical generation profiles were imported into the Sentaurus EMW solver for electrical performance evaluation.

a 3‑D view of the plasmonic GaAs NW solar cell decorated with Au NPs. b 2‑D unit cell used in the simulation. Insets: top view of a single NW with Au NPs and the p‑i‑n junction.

Results and Discussion

We first optimized the diameter‑to‑periodicity ratio (D/P) of the bare GaAs NWs. Figure 2 shows that absorption remains above 90 % for 300–600 nm regardless of D/P, but drops sharply below the bandgap for D/P = 0.2. The best absorption spectrum occurs at D/P = 0.6, where light trapping is strongest. Incorporating Au NPs shifts the absorption peak toward longer wavelengths: at D/P = 0.2, 30–60 nm Au NPs yield a pronounced enhancement between 650 and 800 nm, with the largest gain (≈ 35 %) at 60 nm diameter. In contrast, absorption in the 300–400 nm band decreases by 20–30 % due to localized surface plasmon resonance (LSPR) absorption by the NPs.

The total absorption performance of GaAs NWs with different D/P ratios without Au NPs.

Field‑distribution analysis at 800 nm (Fig. 4) confirms that Au NPs concentrate the electric field along the x‑direction into neighboring NWs, especially for larger NPs. When D/P increases to 0.3 (Fig. 5), absorption remains above 95 % for all NP sizes, but the 60 nm Au NPs again provide the greatest enhancement across 650–800 nm. These results underscore the critical role of LSPR‑induced near‑field coupling in boosting absorption near the GaAs band edge.

Absorption of GaAs NWs with D/P = 0.2 decorated with Au NPs of 30–60 nm compared to bare NW.

2‑D light distribution at 800 nm: (a) electric field magnitude; (b) absorbed power for bare NW and NWs decorated with 30, 40, 50, and 60 nm Au NPs.

Electrical performance calculations (Fig. 9) reveal that Au‑decorated NWs exhibit a higher open‑circuit voltage (0.899 V vs. 0.878 V) and a dramatic increase in short‑circuit current density (24.3 mA/cm² vs. 18.9 mA/cm²). Photoconversion efficiency rises from 12.96 % to 16.92 % at D/P = 0.4, a 24 % relative improvement. The primary driver is the enhanced light trapping by Au NPs, which raises carrier generation rates, especially in the near‑bandgap region.

(a) I–V curves for bare vs. Au‑decorated NWs. (b) Photoconversion efficiency versus D/P for Au‑decorated NWs.

Three mechanisms underpin the observed enhancement: (1) efficient scattering of incident photons by the 60‑nm Au NPs; (2) hot‑carrier injection across the Schottky barrier into the GaAs conduction band; (3) intense near‑field amplification near the LSPR, which drives stronger electron–hole pair generation. These effects collectively increase absorption, photocurrent, and overall efficiency.

Conclusions

We have demonstrated, through rigorous FDTD and electrical simulations, that decorating GaAs nanowire arrays with 60‑nm Au nanoparticles can enhance absorption by up to 35 % at 800 nm and raise photoconversion efficiency by 24 %. The key to this performance is the localized surface plasmon resonance of the Au NPs, which concentrates light within the nanowire and boosts electron–hole generation. This hybrid design offers a scalable pathway to high‑efficiency, low‑cost GaAs nanowire solar cells and invites further experimental validation.