Photoluminescence, Raman, and Hall measurements are reported for Mg doped GaN films grown by molecular beam epitaxy. The compressive and tensile stress determined by the Raman shift of the phonon lines is due to the growth conditions rather than the presence of Mg in the film. The photoluminescence peak of near band-to-band transitions is also shifted to larger (smaller) energies by the compressive (tensile) stress. The study of the longitudinal optical phonon of theA1branch shows that its Raman line shape is affected mostly by the crystalline quality of the film. ©1997 American Institute of Physics.