Effect of Ridge Growth on Wafer Bowing and Light Extraction Efficiency of Vertical GaN-Based Light-Emitting Diodes

In this paper we report on the selective area growth (SAG) of vertical GaN-based light-emitting diodes (LEDs) by low-pressure metal-organic chemical vapor deposition (MOCVD). SAG, under optimized growth conditions, leads to ridge-shaped epilayers with a smooth top surface, devoid of any surface defect structures. The final ridge-shaped vertical LED structures, after the removal of the sapphire substrate by laser lift-off (LLO), exhibit a smaller bowing effect than conventional vertical LED structures. The suppression of lateral strain in the epilayers is responsible for the smaller bowing effect because of the reduction in lateral dimensions. Consequently, the use of SAG LEDs can achieve a 21% higher light output power than conventional vertical LEDs, indicating a significant improvement in light extraction efficiency due to the light guiding pathways offered by the ridge-shaped geometry of the LED structures.