Enhanced light extraction efficiency by surface lattice arrays using blue InGaN/GaN multiple quantum wells

Abstract

The enhancement in light extraction efficiency has been investigated by the incorporation of surface lattice array structures. The surface lattice arrays on GaN-based light-emitting diodes were fabricated by photolithography and inductively coupled plasma (ICP) dry etching processes. The blue light-emitting diode wafers were grown by low-pressure metal–organic chemical vapor deposition. The active InGaN/GaN multiple quantum wells (MQW) were grown on 1.9 μm n-GaN layer. The Mg-doped GaN was deposited on top of the active layer. The thickness of the p-GaN was about 0.14 μm. Three pattern masks were designed for patterning, including square lattice array, triangle lattice array, and honeycomb lattice array. After the patterned areas were pumped by the laser, the devices have exhibited enhanced photoluminescence (PL) intensity at 438 nm. It was attributed to the increased reflection by the lattice array structures. The analysis showed that the improvement in the PL intensity could be as high as 208% with the square lattice array when the etching depth of the arrays was 100 nm. The square lattice array structure was demonstrated to exhibit lower reflectivity of 3–10% at incident angle of 0–20°. In addition, the temperature-dependent photoluminescence results were discussed.