Investigation on compositional pulling effect of InGaN red multiple quantum wells and its remedy

Achieving InGaN quantum wells (QWs) with high indium compositions for red emission presents significant challenges. One challenge is that the red peak is often accompanied by a short-wavelength emission with increased current injection. In this work, such dual-peak emissions in InGaN red multiple QWs (MQWs) were investigated using cross-sectional cathodoluminescence and scanning transmission electron microscopy. This was attributed to the compositional pulling effect. A peak shift from 570 to 600 nm, in conjunction with increased indium composition, was observed across the MQWs from the bottom to the top. By controlling the growth temperature of the individual QWs, short-wavelength emission was suppressed. As a result of this, InGaN red micro light-emitting-diodes (Micro-LEDs) were fabricated, showing a single red emission peak up to a current density of 100 A/cm2 (612 nm) and a peak external quantum efficiency of 7.9% at 5.2 A/cm2. This study not only reveals the presence of the CPE in red InGaN MQWs of high indium compositions but also demonstrates a remedy to achieve single-peak red emission even under high current density operation.