Origins of efficient green light emission in phase-separated InGaN quantum wells

Abstract

Green-light-emitting InGaN/GaN multiple quantum wells (MQWs) with high luminescentefficiency were grown by metalorganic chemical vapour deposition (MOCVD). Themicrostructure of the sample was studied by high-resolution transmission electronmicroscopy (HRTEM) and high-resolution x-ray diffraction, while its optical behaviour wasanalysed in great detail by a variety of photoluminescence methods. Two InGaN-relatedpeaks that were clearly found in the photoluminescence (PL) spectrum are assigned toquasi-quantum dots (516 nm) and the InGaN matrix (450 nm), respectively, due to a strongphase separation observed by HRTEM. Except for the strong indium aggregation regions(511 meV of Stokes shift), slight composition fluctuations were also observed in the InGaNmatrix, which were speculated from an ‘S-shaped’ transition and a Stokes shift of 341 meV.Stronger carrier localization and an internal quantum efficiency of the dot-relatedemission (21.5%), higher than the InGaN-matrix related emission (7.5%), wasdemonstrated. Additionally, a shorter lifetime and ‘two-component’ PL decay were foundfor the low-indium-content regions (matrix). Thus, the carrier transport processwithin quantum wells is suggested to drift from the low-In-content matrix to thehigh-In-content dots, resulting in the enhanced luminescence efficiency of the green lightemission.