Characterization of threading dislocations in GaN epitaxial layers

We investigated Si-doped GaN epitaxial layers on a (0001)-sapphire substrate using a HCl vapor-phase etching technique, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. Three kinds of distinctive etch pits correspond to three different types of threading dislocations, edge, mixed, and screw types. Photoluminescence intensity increases with the decrease in the number of etch pits corresponding to mixed and screw dislocations. The number of etch pits corresponding to edge dislocations, however, did not change. We concluded, therefore, that threading dislocations having a screw-component burgers vector act as strong nonradiative centers in GaN epitaxial layers, whereas edge dislocations, which are the majority, do not act as nonradiative centers. (C) 2000 American Institute of Physics. [S0003-6951(00)00523-4].