PhD research from PDI introduces a new way to probe light absorption in semiconductor nanowires
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Normalized low-temperature (10 K) power-dependent photoluminescence (PL) spectra of GaAs/Al0.3Ga0.7As/GaAs nanowire (NW) arrays with diameters of 140 nm and 80 nm, excited at 633 nm, with corresponding bird’s-eye-view SEM images. The dashed line marks the bulk GaAs heavy-hole exciton (Xhh) transition, and excitation density is color-coded. The 80 nm nanowires show earlier saturation of the carbon-related defect emission (D0,C0) and a stronger blue shift relative to Xhh, indicating earlier Mott transition and enhanced light absorption.
New research based on the PhD thesis of Francisca Marin Largo, carried out within PDI’s Core Research Area (CReA) III-V Nanowires for Optoelectronics, has been published in Advanced Optical Materials. The study presents a new optical approach to probing light absorption in semiconductor nanowires — a long-standing experimental challenge in nanoscale optoelectronics.
Semiconductor nanowires are promising building blocks for future optoelectronic devices, including light emitters, detectors, and solar-energy technologies. However, directly measuring how efficiently such nanostructures absorb light is notoriously difficult due to their extremely small volumes and correspondingly weak absorption signals. Conventional techniques often fail at the single-nanowire level or in sparse nanowire arrays.
To address this challenge, the study introduces photoluminescence spectroscopy as an indirect yet highly sensitive probe of light absorption in highly phase-pure gallium arsenide (GaAs) nanowire arrays and individual nanowires. Rather than measuring absorption directly, the researchers analyse optical signatures that are intrinsically linked to the density of photogenerated charge carriers.
In particular, the saturation behaviour of defect-related emission lines and the transition from excitonic emission to an electron–hole plasma at high excitation densities serve as quantitative indicators of carrier generation. By correlating these spectral features with excitation conditions, the emitted light becomes a fingerprint of how much light is effectively absorbed by the nanowires.
Using this approach, the study reveals a pronounced dependence of light absorption on nanowire diameter. Even for nanowires with comparable material quality and exceptional crystal phase purity, variations in diameter lead to significant differences in carrier generation and optical response. These findings underscore nanowire geometry as a key design parameter for optimising light–matter interaction in nanoscale devices.
Importantly, the method is not limited to GaAs but can be extended to a wide range of semiconductor nanowire systems.
The publication highlights the impact of long-term doctoral research at PDI and demonstrates how PhD projects contribute to advancing both fundamental understanding and experimental methodology in nanoscience and optoelectronics.
Title: Diameter dependence of light absorption in GaAs nanowires evidenced by photoluminescence spectroscopy
Authors: F. Marín Largo, I. Mohamed, O. Brandt, L. Geelhaar
Source: Adv. Opt. Mater., tba, e03215 (2025)
DOI: 10.1002/adom.202503215