Experimental and theoretical studies of phonons in hexagonal InN

The first- and second-order Raman scattering and IR reflection have been st udied for hexagonal InN layers grown on (0001) and (<1(1)over bar>02) sapph ire substrates. All six Raman-active optical phonons were observed and assi gned: E-2(low) at 87 cm(-1), E-2(high) at 488 cm(-1), A(1)(TO) at 447 cm(-1 ), E-1(TO) at 476 cm(-1), A(1)(LO) at 586 cm(-1), and E-1(LO) at 593 cm(-1) . The ratio between the InN static dielectric constants for the ordinary an d extraordinary directions was found to be epsilon(perpendicular to 0)/epsi lon(parallel to 0)=0.91. The phonon dispersion curves, phonon density-of-st ate function, and lattice specific heat were calculated. The Debye temperat ure at 0 K for hexagonal InN was estimated to be 370 K. (C) 1999 American I nstitute of Physics. [S0003-6951(99)01947-6].