Diameter Dependence of Light Absorption in GaAs Nanowires Evidenced by Photoluminescence Spectroscopy

Abstract Semiconductor nanowires are attractive for photovoltaic applications because light absorption can be enhanced compared to planar layers due to the more complex coupling of light with wavelength‐scale matter. However, experimentally, it is very challenging to measure light absorption in single nanowires. Here, photoluminescence spectroscopy is employed as a new method to investigate how the diameter of highly phase‐pure GaAs nanowires affects light absorption. The underlying concept is that the absorption of the exciting laser light influences the photogenerated carrier density and, in turn, spectral features. In particular, it is exploited that both the saturation of a specific defect line and the transition from excitonic to electron‐hole‐plasma recombination occur at well‐defined carrier densities. It is found that absorption is maximized for a diameter of ≈80 nm. This approach may be transferred to other material systems and thus enables straightforward systematic experimental studies of absorption enhancement in single nanowires.