Temperature dependence of the E-2 and A(1)(LO) phonons in GaN and AlN

The frequencies and dampings of the zone-center optical phonons E-2 and A(1 )(LO) in wurtzite-type GaN and AlN layers have been measured by Raman spect roscopy in the temperature range from 85 to 760 K. The GaN layer was grown by metalorganic vapor phase epitaxy and the AlN layer by molecular beam epi taxy both on sapphire substrate. The experimentally obtained frequencies an d dampings are modeled by a theory taking into account the thermal expansio n of the lattice, a symmetric decay of the optical phonons into two and thr ee phonons of lower energy, and the strain in the layers induced by the dif ferent thermal expansion coefficients of layer and substrate. The results w ere used to determine the local temperature of a GaN pn diode in dependence on the applied voltage. (C) 1999 American Institute of Physics. [S0021-897 9(99)05323-2].