# Monolithic GaN-Based Dual-Quantum-Well LEDs with Size-Controlled Color-Tunable White-Light Emission

## TL;DR

This paper introduces a new type of LED that can produce tunable white light by changing the size of the device, eliminating the need for phosphors.

## Contribution

A monolithic GaN-based LED platform with size-controlled color-tunable white-light emission is presented.

## Key findings

- Larger LEDs emit warmer white light with a CCT of 2536 K and CIE (0.501, 0.490).
- Smaller LEDs emit cooler white light with a CCT of 9425 K and CIE (0.224, 0.218).
- Indium segregation in the last QW was confirmed via TEM and EDX analyses.

## Abstract

We report a monolithic GaN-based light-emitting diode (LED) platform capable of color-tunable white-light emission via LED size scaling. By varying the LED size from 800 µm to 50 µm, the injection current density was effectively controlled under constant driving current, enabling precise modulation of carrier distribution within a dual-composition multi-quantum well (MQW) structure. The active layer consists of five lower In0.15Ga0.85N/GaN QWs for blue emission and strain induction, and an upper In0.3Ga0.7N/GaN single QW engineered for red-orange emission. The strain imposed by lower QWs promotes indium segregation in the last QW through spinodal decomposition, resulting in a broadened emission spanning from ~500 nm to 580 nm. High-resolution TEM and EDX analyses directly confirmed the indium segregation and phase-separated structure of the last QW. Spectral analysis revealed that larger devices exhibited dominant emission at 580 nm with a correlated color temperature (CCT) of 2536 K and a CIE coordinate of (0.501, 0.490). As LED size decreased, increased hole injection allowed recombination to occur in deeper QWs, resulting in a blueshift to 450 nm and a CCT of 9425 K with CIE (0.224, 0.218) in the 50 × 50 µm2 LED. This approach enables phosphor-free white-light generation with tunable color temperatures and chromaticities using a single wafer, offering a promising strategy for compact, adaptive solid-state lighting applications.