Effects of quantum-well indium content on deep defects and reliability of InGaN/GaN light-emitting diodes with under layer

Abstract

We investigate the density of defects and the degradation rate in InGaN light-emitting diodes having identical dislocation density and epitaxial structure, but different indium content in the quantum well (QW, 12 %, 16 %, 20 %). Our results, based on combined steady-state photocapacitance, light-capacitance voltage, and degradation measurements indicate that: (i) the density of defects in the superlattice underlayer is identical for the three wafers, indicating good and reproducible growth conditions; (ii) the density of defects within the active region of the devices shows a monotonic dependence on the indium content in the quantum wells. These results, consistent with previous studies on the topic, prove unequivocally the important role of indium in favouring the incorporation of point defects, further clarifying the possible mechanisms of defect formation, and give a quantitative assessment of the related effect; (iii) in step-stress experiments, the degradation rate was found to be much stronger for devices having high indium content in the QW. This result can be explained by considering a decrease in injection efficiency due to the generation or transport of defects, or an increment in defect-assisted Auger recombination terms due to the propagation of defects.