SPATIALLY-RESOLVED LUMINESCENCE STUDIES OF DEFECTS AND STRESS IN ALUMINUM GALLIUM NITRIDE FILMS

Aluminum gallium nitride (AlxGa1-xN) films with x=0 to x=0.36, grown b y metal-organic chemical vapor deposition on sapphire, were characteri zed by cathodoluminescence (CL) imaging and spectroscopy, photolumines cence (PL) spectroscopy, and optical microscopy. In each film, the CL and PL spectra excited from the top surface show a narrow band-edge pe ak and a broad deep-level peak. In some films, the PL spectrum excited from the film-substrate interface (through the sapphire substrate) sh ows an additional narrow peak below the band edge, which is attributed to interfacial defects. CL imaging and optical microscopy reveal two types of large-scale defects: networks of lines, which are probably mi crocracks, and roughly hexagonal raised areas. The hexagonal areas occ ur only in the lower-x films, while the microcrack density increases w ith x. Spatially resolved CL spectra taken near the large-scale defect s show large peak shifts attributed to stress relaxation, and below ba nd-edge peaks attributed to localized states. (C) 1997 American Instit ute of Physics. [S0003-6951(97)03652-8].