Efficiency enhancement mechanism of piezoelectric effect in long wavelength InGaN-based LED

Improving the luminescence efficiency of InGaN-based long wavelength LEDs for use in micro-LED full-colour displays remains a huge challenge. The strain-induced piezoelectric effect is an effective measure for modulating the carrier redistribution at the InGaN/GaN heterointerfaces. Our theoretical results reveal that the hole injection is significantly improved by the diminution of the valence band offset (VBO) of the InGaN/GaN heterointerfaces along the [0001] direction, and inversely, the VBO increases along the [0001] direction. The energy band structures showed that the tensile strain of the GaN film grown on a silicon (Si) substrate could weaken the internal electric field of the InGaN well layer leading to a flattening of the energy band, which increases the overlap of electron and hole wave functions. In addition, the strain-induced piezoelectric polarisation of the InGaN layer on the Si substrate generates opposite sheet-bound charges at the heterointerfaces, which causes a reduction in the depletion region of the InGaN/GaN quantum wells (QWs). A systematic analysis illustrates that the control of the piezoelectric polarisation of the InGaN QW layer is available improve the internal quantum efficiency of the InGaN-based LEDs. The valence band offset of the InGaN/GaN heterointerface grown on Si substrate is the smallest when compared to that of sapphire and SiC. Electrical property analyses revealed the physical mechanism of the efficiency enhancement of InGaN-based LEDs.

Automated summary

Improving the luminescence efficiency of long wavelength InGaN-based LEDs is a challenging task, and strain-induced piezoelectric effect has been shown to be an effective measure. Reduction of valence band offset at InGaN/GaN heterointerfaces significantly improves hole injection. Tensile strain in the GaN film on a silicon substrate increases the overlap of electron and hole wave functions, leading to enhanced efficiency. Control of the strain-induced piezoelectric polarisation of the InGaN quantum well layer further improves the internal quantum efficiency.