Coupling of GaN- and AlN-like longitudinal optic phonons in Ga1-xAlxN solid solutions

Long-wavelength optical phonons of Ga1-xAlxN solid solutions have been identified in a wide compositional range by Raman spectroscopy. The Al and El polar phonon frequencies evolve continuously with x from one-member crystal to the other. The same behavior seems to hold true for the silent B-1 mode, which manifests itself by an interference with an unidentified continuum. Coupling of the longitudinal-optic (LO) modes associated with the two types of bonds, via the macroscopic electric field, is treated by a generalization of the dielectric model [D. T.Hon and W. L,. Faust, J. Appl. Phys. 1, 241 (1973)]. This approach accounts for the observed frequencies and supports the apparent one-mode behavior of the polar LO phonons. (C) 1998 American Institute of Physics.