Energy-Resolved Carrier Recombination beyond the ABC Model Revealed by Ultrafast Transient Absorption Spectroscopy

Ultrafast pump–probe transient absorption spectroscopy provides direct access to both radiative and nonradiative carrier dynamics with energy and time resolution, yet quantitative interpretation is commonly based on phenomenological ABC recombination models that neglect energy resolution. This limitation becomes critical in low-dimensional semiconductor systems, where energy-resolved carrier dynamics may show complex behavior. Here, we introduce an energy-resolved extension of the ABC framework that explicitly resolves this concern. The model is applied to femtosecond transient absorption measurements of GaN/InGaN nanodisk arrays, enabling wavelength-resolved analysis of carrier decay dynamics across the excited-state spectrum. We show that the conventional ABC model fails to reproduce the observed dynamics at higher photon energies, yielding unphysical recombination coefficients, whereas the modified model provides accurate fits and physically meaningful parameters. The extracted time constants span hundreds of picoseconds at higher energies and transition to defect-mediated recombination at lower energies, revealing a clear crossover in the dominant decay mechanisms. This work establishes an experimentally validated framework for energy-resolved carrier recombination analysis, broadly applicable to nanostructures and quantum-confined semiconductor systems.