Cathodoluminescence of epitaxial GaN laterally overgrown on (0001) sapphire substrate. Time evolution with low energy electron beam

The evolution of GaN luminescence under electron beam injection has been st udied by means of in situ cathodoluminescence experiments on various epitax ial lateral overgrown samples. It is shown that the ultraviolet (UV) peak o f undoped materials experiences a decrease of its intensity as well as a no ticeable redshift, while the other extrinsic peaks only experience an inten sity decrease. However, in Mg doped materials the UV peak intensity decreas e is followed by an increase of its intensity which can even reach larger v alues than the initial one. We suggest that all these features are self-con sistently explained by the occurrence of strain relaxation resulting from t he beam enhanced diffusion of vacancies from the free surface, and from the coalescence boundaries towards the bulk. (C) 2001 American Institute of Ph ysics.