Phase-separation microstructures and excellent luminescent performance in strain-relaxed red-emitting bulk InGaN active region

Abstract Bulk InGaN with approximately 20% indium (In) content demonstrates efficient red emission facilitated by strain relaxation-induced phase separation, which challenges traditional multiple quantum well structures. Through various transmission electron microscopy (TEM) techniques, we revealed that strain relaxation induces the spontaneous formation of lamellar, high-In-content clusters along the trench sidewalls. Hyperspectral cathodoluminescence in TEM system directly links these phase-separated domains to red emission. Processed into micro-light-emitting diodes (Micro-LEDs), the bulk InGaN exhibits remarkable luminescent performance, including minimal efficiency droop and only a 4 nm blue shift over a current density range of 5–100 A cm −2 . This work establishes phase separation as a controllable mechanism for bandgap engineering in relaxed III-nitride systems, with significant potential for InGaN-based red Micro-LED applications.