Stress Engineering by Controlling Sapphire Substrate Thickness in 520 nm GaN-Based Light-Emitting Diodes

Controlling the compressive stress in 520 nm GaN-based light-emitting diodes (LEDs) prepared on sapphire substrates with different thicknesses was investigated. As the sapphire substrate thickness is reduced, the compressive stress in the GaN layer is released, resulting in wafer bowing. The wafer bowing-induced mechanical stress alters the piezoelectric fields, which in turn reduces the quantum-confined Stark effect in the InGaN/GaN active region of the LED. Thus, the electroluminescence spectral peak wavelength was blue-shifted, and the internal quantum efficiency was improved by about 11% at an injection current of 20 mA. The LED with an 80-μm-thick sapphire substrate exhibited the highest light output power of 11.5 mW.