A record-long room-temperature photoluminescence (PL) lifetime (τPLRT) of approximately 70 ps was obtained for the sub-bandgap 3.7 eV emission band of a 300-nm-thick c-plane Al0.83In0.17N epilayer for the use in cladding layers of an edge laser structure, which were grown by metalorganic vapor phase epitaxy on a low threading dislocation density nearly lattice-matched GaN substrate. The recorded τPLRT value was twice as long as previously reported ones, indicating half concentration of nonradiative recombination centers. Room-temperature spatially resolved cathodoluminescence intensity images for the 3.7 eV band revealed nearly zero carrier diffusion length, which is consistent with the fact that τPLRT of 70 ps is 1/35 of the near-band-edge emission of the GaN substrate (2.4 ns). As the PL decay curves for the 3.7 eV band were sufficiently fitted by the stretched exponential function, the emission likely originates from extended states such as impurities, point defects, and their complexes, as well as localized states of uneven potential profile.
Lattice-matched Al1− xIn xN / GaN heterostructures with InN mole fraction ( x) of 0.18 have attracted considerable interest for use in GaN-based optoelectronic devices. Because the light emission efficiency ([Formula: see text]) of Al1− xIn xN alloys is far less than that of In xGa1− xN, understanding its causes is essential. For this purpose, room-temperature photoluminescence lifetime ([Formula: see text]), which almost represents the nonradiative recombination lifetime that limits the internal quantum efficiency in low [Formula: see text] semiconductors, of c-plane Al1− xIn xN epilayers nearly and modestly lattice-matched to GaN ([Formula: see text]) was examined. For the epilayers grown on low threading dislocation density (TDD) GaN substrates ([Formula: see text]), [Formula: see text] principally decreased with increasing x, indicating a progressive increase in the concentration of nonradiative recombination centers (NRCs), [Formula: see text]. One of the probable causes is the growth temperature ([Formula: see text]) reduction that is indispensable to incorporate more In, because in insufficient [Formula: see text] regime higher [Formula: see text] is preferred for enhancing the surface migration of adatoms to decrease the concentrations of vacancies that compose NRCs. The Al1− xIn xN epilayers of the same x but grown on high TDD ([Formula: see text]) GaN-on-sapphire templates exhibited shorter [Formula: see text]. Because the diffusion length of minority carriers was nearly zero in the Al1− xIn xN epilayers, the shorter [Formula: see text] indicates higher bulk [Formula: see text] in high TDD epilayers. The Al1− xIn xN epilayers of considerably rough surface morphologies exhibited spatially inhomogeneous [Formula: see text], implying that excited carriers recombined everywhere at InN-rich to InN-poor portions, where [Formula: see text] were likely lower to higher, respectively, than the average due to the deviations in the surface stoichiometry at various non- c-plane surfaces at a given [Formula: see text].
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