Piezoelectric field in highly stressed GaN-based LED on Si (1 1 1) substrate

•Stress states in GaN epilayers grown on Si (1 1 1) and c-plane sapphire were measured.•Large tensile stress is observed in GaN epilayers grown on Si (1 1 1).•The piezoelectric field in the MQW region was monitored using ER spectroscopic method.•The large tensile stress with Si (1 1 1) substrate is regarded as external stress.•External tensile stress compensates for the compressive stress developed in the MQW.

Stress states in GaN epilayers grown on Si (1 1 1) and c-plane sapphire, and their effects on built-in piezoelectric field induced by compressive stress in InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) were investigated using the electroreflectance (ER) spectroscopic technique. Relatively large tensile stress is observed in GaN epilayers grown on Si (1 1 1), while a small compressive stress appears in the film grown on c-plane sapphire. The InGaN/GaN MQWs of LED on c-plane sapphire substrate has a higher piezoelectric field than the MQWs of LEDs on Si (1 1 1) substrate by about 1.04 MV/cm. The large tensile stress due to lattice mismatch with Si (1 1 1) substrate is regarded as external stress. The external tensile stress from the Si substrate effectively compensates for the compressive stress developed in the active region of the InGaN/GaN MQWs, thus reducing the quantum-confined Stark effect (QCSE) by attenuating the piezoelectric polarization from the InGaN layer.