Characterization of threading dislocations in GaN epitaxial layers

We investigated Si-doped GaN epitaxial layers on a (0001)-sapphire substrat e 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 d islocations, edge, mixed, and screw types. Photoluminescence intensity incr eases with the decrease in the number of etch pits corresponding to mixed a nd screw dislocations. The number of etch pits corresponding to edge disloc ations, however, did not change. We concluded, therefore, that threading di slocations having a screw-component burgers vector act as strong nonradiati ve centers in GaN epitaxial layers, whereas edge dislocations, which are th e majority, do not act as nonradiative centers. (C) 2000 American Institute of Physics. [S0003-6951(00)00523-4].