Influence of substrate dislocation density and quantum well width on the quantum efficiency of violet-emitting GalnN/GaN light-emitting diodes

Three series of GaInN/GaN light-emitting diodes (LEDs) emitting at 400 nm with well widths varying between 3 and 18 nm were grown on sapphire, ultra-low dislocation density GaN templates, and free-standing GaN substrates. Photoluminescence and pulsed electroluminescence were systematically investigated. Photoluminescence spectroscopy showed a noteworthy increase in radiative efficiency for GaInN/GaN double-heterostructures or wide wells on low dislocation density substrates. The electroluminescence properties significantly differ for wide well LEDs on sapphire and on low defect density substrates but are comparable for LEDs containing thin single quantum wells. Increasing well width leads to decreasing quantum efficiency at all currents for LEDs on sapphire. The highest overall efficiency is obtained for LEDs with 11 nm and 18 nm thick DHs on GaN templates and free-standing GaN substrates, respectively, at current densities above 200 A/cm2.