Effects of an Asymmetric Barrier Layer on the Structural and Optical Properties of InGaN LEDs

Abstract

InGaN/GaN multiple-quantum-wells (MQWs) with three thinner barriers near the n-GaN layers were grown on c-plane sapphire substrates using metallorganic vapor phase deposition. For LEDs with an asymmetric barrier layer (ABL), high-resolution transmission electron microscopy analysis shows crystalline structure and interface quality are largely unchanged in modified MQWs composed of two kinds of quantum wells with different periods. It was also found that the dependency of strain relaxation on the degree of the exciton localization effect is low due to the InGaN MQWs being pseudomorphically grown on GaN templates. Therefore, the increase of indium segregation could be attributed to variations in the strain status within the MQW region. Experimentally, a large blueshift in the electroluminescence spectra under low level injection conditions provides evidence of the increased biaxial strain in the ABL–containing MQWs. The increase of biaxial strain may be partly accompanied by an increase in the quantum confined Stark effect. However, radiative recombination of the injection carriers in a narrow well will be important for determining the emission properties of the fabricated LEDs. Finally, the proposed LEDs exhibit a 10.8% increase in light output power, presumably because of better carrier distribution and the enhanced localization effect in the InGaN MQWs.