Excitation-dependent spatially resolved photoluminescence in InGaN/GaN LEDs with air-cavity arrays grown on patterned sapphire substrates

Abstract

We investigated the excitation-dependent spatially resolved luminescence properties of InGaN/GaN light-emitting diodes (LEDs) with air-cavity arrays using scanning near-field optical microscopy (SNOM), and quantified the effect of the air-cavity structure on the spatial distributions of light-extraction efficiency, internal quantum efficiency, and external quantum efficiency through experiments and numerical simulations. We found that higher light-extraction efficiency and less stress were always observed in the air-cavity areas. Compared to flat areas, the average light-extraction efficiency of the air-cavity areas was improved by 65%, and the residual stress of the air-cavity center was reduced by 89 MPa, which resulted in increased PL intensity, reduced wavelength shift, and narrowed full width at half maximum. The highest external quantum efficiency and aggravated efficiency droop were found in the air-cavity center. At 3.1 W/cm2, the external quantum efficiency and internal quantum efficiency of the air-cavity center were enhanced by 255% and 223%, respectively.