1. Results and discussion

3. Conclusion In conclusion, thinning the sapphire substrate enables the control of the residual compressive stress developed in the GaN-based near-UV LEDs by changing the curvature of the wafer bowing. The wafer bowing-induced mechanical stress alters the piezoelectric fields, which in turn reduces the QCSE in the InGaN/GaN MQW active region. The reduction in piezoelectric fields causes a blue-shift in EL spectra, an increase in IQE, and improvement of the light output power. In addition, EQE and WPE were optimized because of the enhanced light output intensity.

4. Conclusion The results confirmed that the reduction in the piezoelectric field due to stress relaxation by thinning the sapphire substrate thickness in the InGaN/GaN MQWs caused an enlargement of the effective band gap, and an increase in both the electron–hole wave function overlap and the probability of radiative recombination, along with a corresponding increase in IQE. The simulation results are in a good agreement with the experimental data.