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Time-resolved photoluminescence and light-induced transient grating measurements of GaN epilayers show that the photoluminescence decay can be described by two coupled exponential terms and that carrier mobility and lifetime in GaN epilayers are correlated within the model which accounts for nonradiative carrier recombination predominantly at dislocations. The obtained results demonstrate that migration-enhanced metalorganic chemical vapor deposition (MEMOCVD™) allows for growth of high-quality GaN epilayers on sapphire substrates with the dislocation density close to 108 cm-2, carrier lifetime as long as 2 ns, and ambipolar diffusion coefficient of 2.1 cm2 s-1 corresponding to the hole mobility of approximately 40 cm2 V-1 s-1. [ABSTRACT FROM AUTHOR]

Monte Carlo simulation of phonon-assisted localized exciton hopping has been employed to describe the photoluminescence linewidth variation with temperature and to reveal band potential profile of ternary AlGaN epilayers with different carrier lifetimes. The lifetimes of 30 and 190 ps were experimentally determined in the layers with AlN buffers grown by conventional metal-organic chemical vapor deposition (MOCVD) and by migration-enhanced MOCVD (MEMOCVD™), respectively. The potential profile in AlGaN is shown to consist of double-scaled fluctuations. Exciton hopping in Al0.26Ga0.74N occurs within the random potential fluctuations (on the scale σ≈19 meV) in isolated low-potential regions with the average localization energy dispersed on the scale Γ≈19 meV. Such a pattern of band potential profile was found to be independent on the growth technique used for the deposition of their AlN buffer layers. This implies that the large difference in carrier lifetimes estimated in the AlGaN epilayers with the same Al content is caused by different densities of nonradiative recombination centers rather than by carrier localization in the potential fluctuations. [ABSTRACT FROM AUTHOR]