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Morphology and microstructure evolution of Alo.3Gao.7N epilayers grown on GaN/sapphire templates with low-temperature (LT) AIN interlayers (ILs) by means of metal organic chemical vapor deposition have been investigated by transmission electron microscopy and atomic force microscopy. It is found that the IL improves the surface morphology, and suppresses edge-type threading dislocations (TOs). When the IL thickness is 20 nm, there is the lowest density of the edge-type TO with 8.7xI0 8 cm-2 . But the edge-type TO density increases somewhat as IL thickness increases to 40 nm. It is believed that two mechanisms determine the microstructure evolution of the AlxGal-xN epilayers. One is the TOs suppression effect of LT-AIN ILs that ILs can provide an interface for edge-type TOs termination. Another is the TOs introduction effect of ILs that new edge-type TOs are produced. Due to the lattice mismatch between AIN, GaN and AlxGal-xN, the strain in AlxGal-xN epilayers is modified by inserting the AIN IL, and thus changes the formation of the edge-type TOs.

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