Role of V-defect density on the performance of III-nitride green LEDs on sapphire substrates

Abstract

In this study, we experimentally investigated the role of V-defect density on the performance of green III-nitride LEDs grown on sapphire substrates by metalorganic chemical vapor deposition. We systematically varied the threading dislocation (TD) density from 4 × 108 to 1 × 109 cm−2 by changing the V/III ratio during initial high temperature GaN growth. A 30-period InGaN/GaN superlattice promoted V-defect formation and growth at TDs, where the density of V-defects was correlated to the TD density. By interrupting the LED growth and examining the surface of the active region, we quantified the average size and density of V-defects. In a series of LEDs, we measured a systematic decrease in forward voltage (VF) with V-defect density. At a V-defect density of 5.0 × 108 cm−2 and TD density of 1 × 109 cm−2, green LED devices were demonstrated with λ = 523 nm and VF = 2.94 V at 20 A cm−2. These results highlight the potential of using V-defect engineering to achieve low VF long wavelength LEDs on sapphire substrates, where opening of remaining threading dislocations into V-defects presents an opportunity for further VF reduction.