Temperature dependence of the Raman-active modes in the nonpolar a -plane GaN film

Temperature dependences of the polarized Raman scattering spectra in the backscattering configuration of the nonpolar a -plane (or [ 11 2 ¯ 0 ] -oriented) GaN thin film are analyzed in the range from 100 to 570 K . The nonpolar a -plane GaN film is grown on an r -plane [or ( 1 1 ¯ 02 ) -oriented] sapphire substrate by metal organic chemical vapor deposition. The spectral features of the Raman shifts, intensities, and linewidths of the active phonons modes A 1 ( TO ) , E 1 ( TO ) , and E 2 ( high ) are significantly revealed, and corresponding temperature coefficients are well deduced by the empirical relationships. With increasing the measurement temperature the Raman frequencies are substantially redshifted and the linewidths gradually broaden. The compressive-strain-free temperature for the nonpolar a -plane GaN film is found to be at about 400 K . Our studies will lead to a better understanding of the fundamental physical characteristics of the nonpolar GaN film.