E2 phonon mode

A variation of the E2 mode with the thickness of the AIN buffer layer in MOCVD 750 nm GaN/sapphire structures monitoring biaxial stress has been observed (TABLE 6) [31]. A correlation of E2 phonon modes with exciton energies in photoluminescence has been given [30,31]. 

Figure 1.21 shows typical Raman spectra of the bulk and thin-film ZnO samples [123]. In this particular study, solid lines in both figures indicate Ei, Ai, and E2 phonon modes of ZnO. Dashed-dotted lines mark features observed at 332, 541, and 665 cm , which were assigned to possible multiple-phonon scattering processes [105, 108]. Dotted lines are related to the sapphire phonon mode frequencies (Aig mode 417 and 645 cm Eg mode 379,430,450, 578, and 751 cm ) [110]. For both samples Ai(LO) has not been observed and it was claimed that the scattering cross section for this mode is markedly smaller than that of the Ai(TO) mode due to the destructive interference between the Frbhlich interaction and the deformation potential contributions to the LO phonon scattering in ZnO [107]. Additionally, the occurence of the Ei(LO) mode in both samples was attributed to the breakdown of the selection rule due to the use of the Raman microscope. 

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