Interfacial and defect structures in multilayered GaN/AlN films

A structural assessment of various interfaces formed between successive GaN/AlN layers epitaxially grown on (0001) sapphire, as well as between n-type and p-type GaN is presented, using transmission and high-resolution electron microscopy. The structure of the interfaces between the thick GaN and the thin AlN interlayers (ILs) is investigated in terms of misfit difference and elastic fit of the two crystal lattices. Dense threading dislocations are observed to originate from the substrate/buffer layer interface and their interaction with the successive AlN ILs is studied. Furthermore, basal inversion domain boundaries localized in the n-GaN/p-GaN interface are evaluated.