Stress Engineering During the Fabrication of InGaN/GaN Vertical Light Emitting Diodes for Reducing the Quantum Confined Stark Effect

Abstract

The scope for reengineering the stress in vertical light-emitting diodes (VLEDs) grown Si(111) substrates during the substrate removal and wafer bonding steps in fabrication processing to improve internal quantum efficiency (IQE) is demonstrated. The tensile stress in the GaN layers adjacent to an InGaN/GaN multiple quantum well (MQW) emissive region can be controllably varied in such a way to compensate the pseudomorphic compressive stress in the InGaN layers, and thereby counteract the reduction in the IQE due to the quantum confined Stark effect. A quadratic dependence on the MQW photoluminescence emission wavelength and wafer bow is obtained to enable straightforward strain reengineering through monitoring the change in the wafer bow of the LED epitaxy. The external quantum efficiency of stress-engineered VLEDs bonded onto a 475- $\mu \text{m}$ -thick Si carrier wafer was 25% higher at 300-mA drive current than that of their counterparts bonded onto 675- $\mu \text{m}$ -thick Si substrates using otherwise identical processing.