Raman measurement of the effect of lattice defects on the two‐phonon density of states in ZnO

Abstract

The resonance of the E2High mode of the zinc oxide (ZnO) lattice occurs near a ridge‐like structure of the two‐phonon density of states (DOS). The renormalization of the harmonic frequency of the E2High mode using perturbation‐theory with first‐principles calculations of the two‐phonon DOS is usually used to describe the Raman spectrum of this mode. In this contribution, we tackle the inverse problem; that is, we derive the two‐phonon DOS in ZnO using numerical analysis of Raman measurements of the E2High mode. We vary the temperature to displace the resonance of the E2High mode along the ridge and detect a wide spectrum of the two‐phonon DOS in ZnO. We first derive the two‐phonon DOS by increasing the temperature from 300 K to 1000 K with a 20 K step. Next, we perform the same study but decrease the temperature from 1000 K to 300 K to observe how the two‐phonon DOS changes due to thermal annealing. The results show that lattice defects significantly enhance the two‐phonon DOS, which highlights the need for an effective thermal management strategy when ZnO lattice defects are harnessed for technology applications.

D retention and material defects probed using Raman microscopy in JET limiter samples and beryllium-based synthesized samples

“…It leads to the rise of some new bands. Depending on the material, that bands could be the Phonon Density of States (PDOS)bands ( [21,22], as non-exhaustive examples of materials), or other features induced by other mechanisms [23]. We present here an extended Raman microscopy analysis centered in the 300-1400 cm −1 spectral range, aimed at unravelling the congestion of this spectral range to identify the signature of BeD 2 and to clarify that of defects.…”

Transition from surface phonon-polariton to surface phonon–plasmon-polariton by thermal injection of free carriers

“…Pure phonon anharmonicity and phonon-plasmon coupling are opposite effects in the sense that phonon anharmonicity leads to a decrease in the frequency of the phonon mode with increasing temperature [39,40], while the coupling between phonon and plasma oscillation modes increases the energy of the resulting phonon-plasmon mode above that of the pure longitudinal phonon mode [41]. Thus, the linear temperature dependence of the frequency of the E 1 symmetry mode observed in the temperature range 280-665 K indicates a typical three-phonon anharmonic process of a pure phonon and shows no effect of thermally injected free carriers in this temperature range [42][43][44]. However, the increase of the frequency of this mode and the appearance of phonon-plasmon mode resonance at a higher frequency at the temperature of 810 K and above clearly indicates that above a threshold temperature, the hot electron density becomes high enough to contribute to the reflectivity spectrum.…”