Revealing the importance of light extraction efficiency in InGaN/GaN microLEDs via chemical treatment and dielectric passivation

Chemical etching and Al2O3 dielectric passivation were used to minimize nonradiative sidewall defects in InGaN/GaN microLEDs (mesa diameter=2-100 mu m), resulting in an increase in external quantum efficiency (EQE) as the LED size was decreased. Peak EQEs increased from 8%-10% to 12%-13.5% for mesa diameters from 100 mu m to 2 mu m, respectively, and no measurable leakage currents were seen in current density-voltage (J-V) characteristics. The position and shape of EQE curves for all devices were essentially identical, indicating size-independent ABC model (Shockley-Read-Hall, radiative, and Auger recombination) coefficients-behavior that is not typical of microLEDs as the size decreases. These trends can be explained by enhancement in light extraction efficiency (LEE), which is only observable when sidewall defects are minimized, for the smallest LED sizes. Detailed ray-tracing simulations substantiate the LEE enhancements.