Improvement of crystal quality and optical property in (11−22) semipolar InGaN/GaN LEDs grown on patterned m-plane sapphire substrate

Semipolar GaN layers were grown on the m-plane hemispherical patterned sapphire substrates (HPSS) using metal organic chemical vapor deposition in order to reduce the defect density and enhance the extraction efficiency of light. The roughness values of the GaN surface grown on the planar sapphire and the HPSS were 30 and 23 nm root-mean-square roughness for a 20×20-μm2 area, respectively. The reduction of basal stacking fault density was demonstrated by x-ray rocking curve of off-axis planes and cross-sectional transmission electron microscopy. The low-temperature photoluminescence measurement showed that the near band-edge emission from HPSS semipolar GaN was approximately one order of magnitude stronger than that from planar semipolar GaN layer.The InGaN light emitting diode grown on the HPSS showed an output power approximately 1.5 times that on the planar m-sapphire.

► Semipolar GaN layer on the HPSS showed was grown to be a pit-free and mirror-like surface.
► On-axis and off-axis XRD measurement and cross-sectional TEM results confirm that the HPSS has efficiently reduced the BSFs.
► Semipolar LED on the HPSS shows about 1.5 times higher output power than does the planar LED.