Strain visualization enabled in dual-wavelength InGaN/GaN multiple quantum wells Micro-LEDs by piezo-phototronic effect

Optical strain sensor for stress visualization is a significant topic in biomechanical imaging or electronic skin. In this study, the dual-wavelength InGaN/GaN multiple-quantum-wells (MQWs) micro light emitting diode (Micro-LED) is demonstrated with color response under mechanical stimulation by piezo-phototronic effect. The peak intensity of green light increases by about 37%, while the blue decreases by 10% at the external strain of 0.20%. Simultaneously, the intensity integral ratio of green and blue light changes from 43:57–53:47, leading to the display color shift from light blue to turquoise significantly. It is noted that electrical injection shows a greater color response than photoluminescence, indicating that the piezo-phototronic effect changes both the recombination in MQWs and the carrier injection. The different piezoelectric modulation between green QW and blue QW lies on the different strain-induced piezoelectric polarized charges in the interface of InGaN QWs, revealed by experiments and APSYS simulation in details. This study is of high significance for the development of optical-based stress sensor with strain visualization and high spatial resolution for smart sensing and micro-opto-electromechanical systems.