Surface phonon polariton modes of wurtzite structure AlxGa1-xN thin film

The polar phonon polariton modes in a wurtzite thin film structure are theoretically investigated in the present paper. It is confirmed that there are two types of phonon polariton modes, i.e. the surface phonon polariton (SPP) modes and the continued phonon polariton (CPP) modes in wurtzite thin film systems. The frequency ranges of the SPP and CPP modes are discussed in detail. The dispersive equation of the SPP modes is also deduced. Numerical calculations on AlxGa1-xN thin film structures reveal that, form a given free wave number k(i) in the x-direction there are two branches of SPP modes in general. The Al concentration of x, of AlxGa1-xN materials and the thickness d of the wurtzite thin film have an important influence on the dispersive properties of the polariton modes especially as the thickness d is small. Our calculated results are completely consistent with the recent experimental observations in AlxGa1-xN thin film systems. We confirm that the SPP modes observed are the low-frequency branches of SPP mode. Furthermore, the frequency values of the high-frequency branches of SPP modes are explicitly given and a possible method for observing these high-frequency SPP modes is also brought forward. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimPhysics, Condensed MatterSCI(E)6ARTICLE1164-16924