Suppressed spectral shift in InGaN red micro-light-emitting diodes via preserved localized-state recombination

Micro-light-emitting diodes (µLEDs) are promising for next-generation micro-displays, but spectrally stable InGaN red emission remains difficult because high-indium-content quantum wells suffer from severe current-induced blueshift and spectral broadening. Here, we demonstrate 5 × 5 µm² InGaN red µLEDs with strongly suppressed spectral drift using an AlN interlayer/low-temperature p-GaN design. Compared with the reference µLEDs, which show a 56 nm blueshift from 4 to 100 A/cm², the engineered devices exhibit blueshifts of only 14 nm from 4 to 100 A/cm² and 24 nm up to 600 A/cm², together with a small linewidth variation over the common 4-100 A/cm² range. Comparative atom-probe tomography reveals nanoscale In-composition fluctuations in both samples, with distinct local compositional contrast retained in the analyzed upper-QW region of the engineered sample; this local observation is not interpreted as a broader ensemble-scale distribution of radiative transition energies. Temperature- and power-dependent photoluminescence further indicate a localized-state ensemble that is more robust against thermal and carrier-density perturbations. These correlated observations are consistent with weaker redistribution toward higher-energy recombination channels in the engineered sample. The engineered µLEDs reach a peak EQE of 5.9% at 612 nm, providing a route toward spectrally stable InGaN red µLEDs.