Phonon dynamics and anharmonicity in phase segregated structural domains of MgZnO film

Abstract

Phonon decay channels and anharmonicities in embedded domains in MgZnO film were studied via selective resonant Raman scattering at the elevated temperature regime up to 870 K. The resonant conditions provided by excitation with different ultraviolet laser lines enabled the detection of longitudinal optical (LO) phonons from domains with the wurtzite structure, and domains with the cubic rocksalt structure which lack inversion symmetry due to alloying. The phonon behavior was modeled in terms of three- and four-phonon decay processes using Ridley and Klemens type decay processes. It is found that the wurtzite phase displays dominantly three-phonon decay with a small four-phonon component. In contrast, the cubic phase displays a higher degree of anharmonicity in which the four-phonon processes contribute significantly to the temperature dependent frequency shift. At the elevated temperature range, the LO frequency shift rate is ∼−2.6 × 10−2 cm−1/K for the wurtzite structure while that of the cubic exhibits a much larger shift rate of ∼−1.6 × 10−1 cm−1/K. The larger anharmonicity of the domains with the cubic structure is discussed in terms of strain and deformation effects.