Anharmonic phonon decay in cubic GaN

Abstract

We present a Raman-scattering study of optical phonons in zinc-blende (cubic) GaN for temperatures ranging from 80 to 750 K. The experiments were performed on high-quality, cubic GaN films grown by molecular-beam epitaxy on GaAs (001) substrates. The observed temperature dependence of the optical phonon frequencies and linewidths is analyzed in the framework of anharmonic decay theory, and possible decay channels are discussed in the light of density-functional-theory calculations. The longitudinal-optical (LO) mode relaxation is found to occur via asymmetric decay into acoustic phonons, with an appreciable contribution of higher-order processes. The transverse-optical mode linewidth shows a weak temperature dependence and its frequency downshift is primarily determined by the lattice thermal expansion. The LO phonon lifetime is derived from the observed Raman linewidth and an excellent agreement with previous theoretical predictions is found.

Temperature dependence of Raman-active phonons and anharmonic interactions in layered hexagonal BN

“…The values we obtain for the anharmonic coupling potentials are similar to those reported in c-GaN (Ref. [20]) and in ZnO [19]. The model fit to the data is plotted as a solid line in Fig.…”

“…The impurity relaxation time can be estimated from the impurity background broadening obtained from the above analysis, and we find τ I ∼ 8.7 × 10 −13 s. Then, from the Raman FWHM, the anharmonic relaxation times at RT and 80 K are determined to be 3.3 and 4.4 ps, respectively. These values, which are only slightly higher than those reported for the LO mode of c-GaN (2.0 and 4.2 ps) [20], indicate a faster thermalization compared to graphite, where a value of 7 ps was estimated from time-resolved spectroscopy measurements [24].…”

“…The imaginary part of the phonon self-energy accounts for the Raman line shape broadening due to the finite phonon lifetime caused by anharmonic phonon decay. This analysis has been successfully applied to a wide number of semiconductors [17,19,20,30]. In metallic systems, electron-phonon coupling can also limit the phonon lifetime by creating electron-hole pairs.…”

“…Raman scattering can provide valuable information about phonon lifetimes and the anharmonic decay of phonons into other phonons that conserve energy and momentum [17][18][19]. Recently, we have reported a Raman scattering study of anharmonic decay processes and phonon lifetime in zinc-blende type cubic GaN [20]. Whereas phonon anharmonicities have been studied in detail by means of Raman scattering experiments in the closely related graphite and graphene structures [21,22], no information exists in the literature about phonon anharmonic decay in h-BN.…”

Surface acoustic wave velocity and elastic constants of cubic GaN

“…9 More recently, the anharmonic phonon decay in c-GaN has been investigated by means of Raman scattering. 10 Whereas Brillouin scattering measurements providing a reliable experimental determinaton of the elastics constants were reported in wurtzite GaN, 11,12 the present knowledge of the elastic constants of cubic GaN comes mainly from molecular-dynamics and densityfunctional-theory calculations. [13][14][15][16][17][18] To our knowledge, only one of the three independent elastic constants of c-GaN has been experimentally determined by means of picosecond acoustic experiments.…”