Controlling the defect density to improve the output power of InGaN/GaN-based vertical light-emitting diodes by using substrates patterned with SiO2 lenses

Abstract

In this study, we investigated the effect of SiO2 lenses on the output power of InGaN/GaN-based vertical light-emitting diodes (VLEDs; wavelength=445nm) and compared the results to those of reference VLEDs without the SiO2 lenses (planar samples). Arrays of SiO2 lenses (pitch=3m, width=2.5m, height=1.0m) were formed on c-plane sapphire substrates. The external quantum efficiency (EQE) of the packaged VLEDs with planar and patterned substrates was characterised. At 5mA, the EQE of the patterned samples was 150% higher than that of the planar samples. A patterned, N-polar, n-GaN sample contained far fewer nanopipes (approximately 2.2 x 10(5)cm(-2)) than a planar n-GaN sample (approximately 2.4 x 10(6)cm(-2)). Furthermore, the patterned samples contained far fewer threading dislocations (approximately 1.0 x 10(8)cm(-2)) than the planar samples (approximately 5.0 x 10(8)cm(-2)). Scanning electron microscopy (SEM) images showed that the photoelectrochemical (PEC)-etched patterned samples contained cones that were 150% larger than that of the PEC-etched planar samples. In addition, SEM images, cathode luminescence measurements and finite-difference time-domain simulations were used to characterise the improved light output of the patterned samples.