Lifetime Tests and Junction-Temperature Measurement of InGaN Light-Emitting Diodes Using Patterned Sapphire Substrates

The authors demonstrate nitride-based blue light-emitting diodes with an InGaN/GaN (460 nm) multiple quantum-well structure on the patterned sapphire substrates (PSSs) compared with conventional sapphire substrates (CSSs) using metal-organic chemical vapor deposition. According to full-width at half-maximum of high-resolution X-ray diffraction and transmission electron microscopy micrographs, the dislocation density of GaN epilayers grown on the PSS was lower than those of the CSS. It was found that the output power of devices on PSS was 26% larger than that of CSS. The lifetime defined by 50% loss in output power was 590 and 305 h at 85 degC for the PSS and CSS, respectively. It was also found that the junction temperature and thermal resistance were smaller for the PSS. These improvements are attributed to the reduction in dislocation density using PSS structure