Experimentally study electron overflow from quantum wells into p-side GaN and its effect on the efficiency droop in InGaN/GaN blue-light-emitting-diodes

We experimentally study the electron overflow in InGaN/GaN blue light emitting diodes (LEDs) by measuring the electroluminescence (EL) emission spectra from p-type InGaN/GaN superlattices (SLs) adjacent to the quantum well (QW) active region. The integrated EL intensity ratio of the SL peak to quantum well peak was calculated to reveal the dependence of electron overflow from active region on current density. Our experimental results indicate that the electron overflow from the active region at both low and high current densities, and no saturation is observed even at the maximum current density (280 A/cm2) applied. It is found that both direct electron leakage and Auger assisted leakage contribute to the electron overflow. Further analyses reveal that at low current densities (less than 150 A/cm2) direct electron leakage dominates the mechanism for electron overflow, and simultaneously for efficiency droop, while electron overflow is mainly caused by Auger assisted leakage at high current density. These results identify the main mechanisms for efficiency droop of LEDs at different current density regimes.