III-Nitrides based light-emitting diodes (LED) have greatly attracted considerable attention due to their use in a range of applications for illumination and are often operated at high drive currents to achieve high emission powers. In order to have enough emission optical powers, LEDs with high internal quantum efficiency (IQE) and light extraction efficiency (LEE) as well as external quantum efficiency (EQE) are required. In this work, first, we explored the optical and material properties of GaN-based polar and semipolar blue LEDs grown on c-plane patterned sapphire substrate (PSS) and free-standing GaN (FS-GaN) substrate, respectively. By analyzing these properties, we were be able to achieve high IQE, LEE, and EQE values using novel designs of the epi structure and LED package.

At UCSB, by using a novel vertical transparent ZnO-stand LED (VT-LED) package to reduce the loss of photons in the absorptive materials (p-type GaN, indium-tin oxide, and silver header, etc.), high LEE of 76 and 75% can be achieved for GaN-based LEDs grown on PSS and FS-GaN substrate, respectively. In this study, we also find a close agreement between simulating and experimental results.

On the other hand, in order to achieve high IQE and EQE for blue LEDs at high current densities (> 100 A/cm2), low-carrier-density structure design is the key to address efficiency droop (J-droop) and thermal droop (T-droop), in which IQE decreases with increasing the injection current and temperature. A compositionally step-graded (CSG) InGaN quantum barrier (QB) and a single 12-nm-thick quantum well (SQW) structure have been applied in polar (0001) and semipolar (2021) blue LEDs, respectively, to mitigate Shockley-Read-Hall (SRH) and Auger recombination, and carrier leakage by lowering the carrier density in the active region of the LED. As a consequence, high EQE of ∼ 46 and 50% and low thermal droop ratios of ∼ 16 and 10% (when the temperature is elevated from 20 to 100°C) can be achieved for polar (0001) and semipolar (2021) blue LEDs, respectively, at the current density of 100 A/cm2.

Also, some material characterizations have been done to investigate material properties of polar (0001) and semipolar (202-1-) GaN-Based LEDs.