Microscopic Understanding of V-Shaped Pits Induced Quantum Barriers and Localized-State Luminescence in High-Indium-Content InGaN/GaN Multiple-Quantum-Well LEDs

In this study, microstructural characterization with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), variable-temperature steady-state and time-resolved photoluminescence (PL), PL-excitation spectral measurements, and calculations based on the newly developed quantum many-body localized-state ensemble (MB-LSE) luminescence theory were systematically conducted on high-indium-content InGaN/GaN multiple-quantum-well light-emitting diodes (MQW LEDs). Based on the atomic-number Z dependence of the image contrast, an analytical expression was advocated to estimate the localized-state distribution of InGaN alloys from STEM images of typical V-shaped pits. Central energies of the localized states in the right vicinity region and the bottom MQW region of a V-shaped pit were determined to be 2.80 and 2.20 eV, respectively. Calculations of variable-temperature PL spectra and lifetimes with the MB-LSE model led to elucidation of two critical energies (∼2.886 and 2.217 eV): the central energy of overall localized-state distribution and quantum tunneling energy dominating luminescence thermal behaviors, respectively. The study thus sheds some light on the complicated luminescence mechanism of high-indium-content InGaN/GaN MQW LEDs with many V-shaped pits.