Local vibrational modes in Mg-doped GaN grown by molecular beam epitaxy

Local vibrational modes in the region of the acoustic and optical phonons a re reported for Mg-doped GaN grown by molecular beam epitaxy. The modes, st udied by Raman spectroscopy, appear in addition to the known modes in the h igh-energy region around 2200 cm(-1). We suggest disorder-activated scatter ing and scattering from Mg-related lattice vibrations to be the origin of t he low-energy modes. Our assignment is supported by calculations based on a modified valence-force model of Kane. Temperature-dependent measurements b etween 4 and 300 K exclude an electronic Raman-scattering mechanism. We als o report a new line at 2129 cm(-1) and discuss the origin of all five obser ved high-energy modes. (C) 1999 American Institute of Physics. [S0003-6951( 99)00822-0].