Optical and structural characteristics of high-performance InGaN/GaN multiple quantum well light-emitting diodes: effects of nano-structural features

Abstract

Optical and structural properties of InGaN/GaN multi-quantum well (MQW) structures with different well width, influenced by the nano-structural features in the MQWs, were investigated by optical measurements of photoluminescence (PL), photoluminescence excitation (PLE) and time-resolved photoluminescence (TRPL), as well as structural analysis methods, such as high-resolution X-ray diffraction (HRXRD) and high-resolution transmission electron microscopy (HRTEM) measurements. Due to the quantum confined Stark effect (QCSE), larger Stokes shift is induced with larger well width. Thermally activated carrier screening model is established to well describe the so-called S-shaped spectral shift with temperature. Inhomogeneous line-width broadening induced by piezoelectric field is found to be dominant at low temperature, while homogeneous line-width broadening due to phonon scattering takes over at higher temperature. Additionally, two activation energies are extracted from the Arrhenius plot of PL intensity. One is assigned to be the exciton binding energy and the other one the confinement energy of electrons in the quantum well. TRPL study further indicated that the radiative lifetime was decreased with the decreased well width. All these are associated with the In-composition fluctuation and nano-structures in the MQWs.