Wurtzite phonon mode frequencies

The phonon mode frequencies of wurtzite- and rocksalt-structure Mg Zni- O thin films vs. x, as obtained by combination of Raman scattering and IRSE, are plotted for 0 < x < 1 in Fig. 3.13. 

Fig. 3.13. Phonon-mode frequencies of wurtzite-structure PLD-grown Mg Zni- O thin films with Ai-symmetry (panel a, triangles) and Fi-symmetry (panel b, triangles), and of rocksalt-structure PLD-grown Mg Zni- O thin films (circles in both panels) vs. x [43,62,72,74], Open and solid symbols represent TO- and LO-modes, respectively. The dashed lines are linear approximations of the rocksalt-structure phonon modes from [74], the solid lines represent MREI calculations for the wurtzite-structure phonon modes redrawn from [132]. The shaded area, marks the composition range, where the phase transition occurs. Reprinted with permission from [74]...

Vibrational properties of MgxZni 3(0 have been measured over the entire compositional range covering the wurtzite structure on the low end and cubic on the high end. The phonon mode frequencies of Mg Zni- O versus x, as obtained by utilizing... 

Wurtzite ZnO structure with four atoms in the unit cell has a total of 12 phonon modes (one longitudinal acoustic (LA), two transverse acoustic (TA), three longitudinal optical (LO), and six transverse optical (TO) branches). The optical phonons at the r point of the Brillouin zone in their irreducible representation belong to Ai and Ei branches that are both Raman and infrared active, the two nonpolar 2 branches are only Raman active, and the Bi branches are inactive (silent modes). Furthermore, the Ai and Ei modes are each spht into LO and TO components with different frequencies. For the Ai and Ei mode lattice vibrations, the atoms move parallel and perpendicular to the c-axis, respectively. On the other hand, 2 modes are due to the vibration of only the Zn sublattice ( 2-low) or O sublattice ( 2-high). The expected Raman peaks for bulk ZnO are at 101 cm ( 2-low), 380 cm (Ai-TO), 407 cm ( i-TO), 437 cm ( 2-high), and 583 cm ( j-LO). 

In this chapter, we review recent studies of optical phonons in relation to the anisotropic strain in GaN heteroepitaxial layers and quantum dots (QDs) with nonpolar orientations. For reasons of comparison, results on anisotropically strained c-plane GaN films grown on a-plane sapphire is also presented where appropriate. The application of GIRSE and Raman scattering to the studies of optical phonon frequencies of anisotropic wurtzite GaN is described to reveal the phonon mode behavior. The assessment of anisotropic strain components in a-plane GaN films and their evolution with thickness... 

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