Far UV resonant Raman scattering in hexagonal Ga1-xAlxN alloys

UV excited (244 nm) Raman spectra of Ga1-xAlxN layers (0 < x less than or e qual to 0.85) grown on sapphire substrates by metal-organic vapor phase epi taxy have been acquired. In contrast with photoluminescence governed by dee p center recombinations in aluminum-rich layers (x > 0.55), strong multiple A(1)(LO)-phonon scattering mediated by Frohlich electron-phonon interactio n gives evidence for electronic excitations across the band gap as intermed iate states of the Raman process over the whole compositional range. Alloyi ng and temperature effects are used to obtain the resonant profile of the A (1)(LO) line intensity. The shift in line position, within spectra recorded under visible and ultraviolet excitation, is attributed to the probing of local compositional fluctuations by the long-range Frohlich interaction. (C ) 1999 Elsevier Science Ltd. All rights reserved.