Optical characterization of Mg-doped GaN films grown by metalorganic chemical vapor phase deposition

Scanning electron microscopy, micro-Raman, and photoluminescence (PL) measu rements are reported for Mg-doped GaN films grown on (0001) sapphire substr ates by low-pressure metalorganic chemical vapor phase deposition. The surf ace morphology, structural, and optical properties of GaN samples with Mg c oncentrations ranging from 10(19) to 10(21) cm(-3) have been studied. In th e scanning micrographs large triangular pyramids are observed, probably due to stacking fault formation and three-dimensional growth. The density and size of these structures increase with the amount of magnesium incorporated in the samples. In the photoluminescence spectra, intense lines were found at 3.36 and 3.31 eV on the triangular regions, where the presence of cubic inclusions was confirmed by micro-Raman measurements. The excitation depen dence and temperature behavior of these lines enable us to identify their e xcitonic nature. From our study we conclude that the interface region betwe en these defects and the surrounding wurtzite GaN could be responsible for PL lines. (C) 2000 American Institute of Physics. [S0021-8979(00)07719-7].