Enhanced Extraction Efficiency of InGaN/GaN Light-Emitting Diodes by Liquid Phase-Deposited Zinc-Oxide-Textured Window Layer

This paper proposes a method of improving the extraction efficiency of InGaN/GaN light-emitting diodes (LEDs) using textured zinc oxide (ZnO) prepared by liquid phase deposition (LPD). The treatment solution for liquid-phase-deposited ZnO (LPD-ZnO) consisted of hydrochloric acid (HCl) saturated with ZnO powder. The deposition temperature was maintained at 30 ^°C using a temperature-controlled water bath system. Atomic force microscope images of the LPD-ZnO indicate that the root-mean-square (RMS) roughness of the LPD-ZnO is dependent on the HCl concentration. As compared with conventional the InGaN/GaN LED, the extraction efficiency of the InGaN/GaN LED with the LPD-ZnO-textured layer increases in conjunction with RMS roughness. The maximum light output intensity enhancement of 48% for the InGaN/GaN LED with an RMS roughness of 16.26 nm occurred under a driving current of 20 mA. The calculated optical intensity of the InGaN/GaN LED with a bumplike LPD-ZnO-textured surface indicates that the optimum RMS roughness of the textured surface layer applied to InGaN/GaN LEDs is approximately 16 nm, which agrees with the experimental results. The InGaN/GaN LED with LPD-ZnO with an RMS roughness of 16.26 nm shows a wide light output divergence angle, which satisfies the requirement of the applications of a backlight source.