High-luminous efficacy green light-emitting diodes with InGaN/GaN quasi-superlattice interlayer and Al-doped indium tin oxide film

Abstract

High-luminous efficacy green light-emitting diodes (LEDs) with InGaN/GaN quasi-superlattice (QSL) interlayer and Al-doped indium tin oxide (ITO) current spreading film have been demonstrated. The photoluminescence mapping results revealed that the 2-inch green LED wafer with the QSL interlayer had a longer average peak wavelength as compared to that without the QSL interlayer. In addition, the forward voltage was decreased and the light output power was considerably improved for the green LED chips fabricated from the wafer with the QSL interlayer. Then, an Al-doped ITO film was employed in the green LEDs showing a further improvement in external quantum efficiency. It was mainly ascribed to the increased internal quantum efficiency by analyzing the injection efficiency, light extraction efficiency and X-ray photoelectron spectroscopy spectrum. Finally, at an injected current of 20 mA, a high luminous efficacy of 264.7 lm/W and peak wavelength of 537.2 nm was achieved for the green LEDs with a chip-on-board silicone encapsulation. We determine that the high luminous efficacy was attributed to the improved electrical and light output performance of the LEDs due to the use of the InGaN/GaN QSL interlayer, the Al-doped ITO and the chip packaging structure.