High-power low-droop violet semipolar (303¯1¯) InGaN/GaN light-emitting diodes with thick active layer design

Abstract

Devices grown on nonpolar and semipolar planes of GaN offer key performance advantages over devices grown on the conventional c-plane, including reduced polarization fields. This allows for a wider design space on semipolar planes for light emitting diodes (LEDs) to address the problem of efficiency droop at high current densities. LED structures with very thick (10–100 nm) InGaN single-quantum-well/double heterostructure active regions were grown using conventional metal organic chemical vapor deposition on semipolar (303¯1¯) free-standing GaN substrates and processed and packaged using conventional techniques. Simulated band diagrams showed reduced polarization fields on the (303¯1¯) plane. The calculated critical thickness for misfit dislocation formation is higher on the (303¯1¯) plane than on other semipolar planes, such as (202¯1¯), allowing for thicker active regions than our previous work to further reduce droop. The higher critical thickness was confirmed with defect characterization via cathodoluminescence. A trend is demonstrated in lower efficiency droop for devices with thicker active regions. Thermal droop characteristics of these devices are also presented. These observed results were utilized to demonstrate over 1 W of output power at a current density of 1 kA/cm2 from a single 0.1 mm2 LED device.