Light emission from several-atom In–N clusters in wurtzite Ga-rich InGaN alloys and InGaN/GaN strained quantum wells

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In order to understand the mechanism of light emission and to seek the special In-related crystal microstructures associated with the elusive electron localization centers, we consider four representative In configurations (uniform, small In–N clusters, short In–N chains, and a combination of clusters and chains) in wurtzite Ga-rich In x Ga 1− x N alloys and In x Ga 1− x N/GaN strained quantum wells (QWs), respectively, and investigate their electronic structures using powerful first-principles calculations. We find that the several-atom In–N clusters can exist stably with a high concentration due to their small formation energy and play an important role in Ga-rich In x Ga 1− x N alloys and QWs. Unlike previous In–N-chain or In-rich quantum dot-like viewpoints, as radiative recombination centers, the several-atom In–N clusters, especially the c-plane clusters, highly localize electrons at the valence band maximum (VBM) and dominate the light emission if clusters and chains coexist in Ga-rich In x Ga 1− x N alloys. The microscopic arrangement of In atoms in the alloy strongly influences its band gap and bowing parameter. Moreover, the strains of the In x Ga 1− x N layer can enhance the electron localization of the VBM state around the clusters. The physical reasons have been analyzed in-depth. Our results are in good agreement with experiments and other calculations.