Exciton dynamics and surface recombination in blue-emitting InGaN/GaN nanopillars

Abstract

We systematically investigated the effect of lateral size scaling on exciton dynamics and surface recombination in InGaN/GaN quantum-well nanopillars fabricated from a blue-emitting planar InGaN-based LED template using hydrogen-environment anisotropic thermal etching. Nanopillar arrays with a wide diameter range (D) were patterned on the same wafer while maintaining fixed In composition and well thickness, enabling the disentanglement of three recombination processes governing exciton dynamics through micro-photoluminescence and micro-time-resolved PL (micro-TRPL) measurements at low and room temperatures: (i) accelerated radiative recombination resulting from strain relaxation, (ii) suppressed nonradiative recombination due to the dislocation–isolation effect, and (iii) enhanced surface recombination at the lateral sidewalls. A systematic blueshift with decreasing D was observed and is consistent with an analytical model incorporating strain relaxation, internal electric fields, and quantum confinement. Micro-TRPL analysis enabled the separation of volume and surface recombination rates, the quantification of the surface recombination velocity, and the establishment of a simple exciton-diffusion model explaining the transition from a D−1 dependence to saturation behavior when D becomes comparable to the diffusion length Ld. For intermediate sizes (D ≈ Ld), PL decay curves exhibited two distinct components attributable to spatially separated regions with and without access to lateral surfaces, further validating the exciton-diffusion-driven saturation mechanism. These findings provide quantitative nanoscale design guidelines and highlight the critical roles of surface passivation and diffusion management in optimizing the internal quantum efficiency of InGaN-based nanostructures.