Interplay between efficiency, spectral linewidth, and strain engineering of InGaN-based green LEDs grown on Si

This work presents an interference-free spectroscopic approach to address a long-standing challenge in InGaN-based LEDs grown on Si: resolving the interplay between strain engineering, efficiency, and spectral linewidth. By removing the Si substrate and intentionally roughening the exposed N-face GaN surface to eliminate Fabry–Pérot interference fringes, it is clearly revealed that the compressive strain accumulated in the film prior to quantum well growth governs an inverse relationship between efficiency and spectral linewidth. Higher compressive strain degrades internal quantum efficiency (IQE) but narrows the emission, whereas lower strain boosts IQE at the cost of a slightly broader linewidth. The LEDs with an AlN single-layer buffer (i.e., reduced lattice mismatch) relax via localized state formation, yielding a high IQE of ∼80% with 39 nm FWHM. In contrast, LEDs with a conventional multi-layer AlN/AlGaN buffer (i.e., large mismatch) relax mainly via the generation of defects, resulting in a huge drop in IQE (37%) but a narrower linewidth of 32 nm. Electroluminescence from vertical thin-film LED chips further corroborates this proposed model. This work provides a clear, physically grounded roadmap for rational strain management in InGaN-based LEDs, which is a critical step toward optimizing their performance for solid-state lighting and micro-LED display applications.