Influence of pillar-and hole-patterned sapphire substrates on MOVPE grown GaN bulk and LED structures

Abstract

Bulk GaN material and LED structures on pillar-patterned sapphire substrates （PSS-p） and hole-patterned sapphire substrates （PSS-h） were grown by MOCVD and the characteristic was compared in detail. X-ray diffraction and atomic force microscope measurements show a better crystal quality and surface morphology of GaN on PSS-h than that of GaN on PSS-p, which is due to the lateral growth of GaN on PSS-h observed from cross-sectional scanning electron microscopy. Furthermore, the output power of LED on PSS-p and PSS-h with 20 mA injection current are 46% and 33% higher than LED on conventional sapphire substrate, respectively. The temperature-dependent photoluminesence measurements indicate that the internal quantum efficiencies of all samples are quite close. Therefore, the airgaps between GaN and PSS-h act against the improvement of light extraction efficiency.