Investigations on correlation between photoluminescence images of an LED epi-wafer and characteristics of LED chips

Photoluminescence (PL) imaging is employed in order to inspect InGaN/GaN LED epi-wafers. The image shows a map of integrated PL intensity over the wafer and dark spots with degraded luminescence properties. Dark spots with various sizes indicate areas with nonradiative defects showing that the nonradiative recombination coefficient increases with the size. The PL images are compared with data obtained from LED chips on the wafer after fabrication process. The characterization results for LED chips show that most of the chips fabricated on the dark spots have degraded properties. The result indicates that PL imaging of epi-wafers could be an inspection tool to predict properties of LED chips.