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

Abstract

The resonance of the (Formula presented.) 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 (Formula presented.) 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 (Formula presented.) mode. We vary the temperature to displace the resonance of the (Formula presented.) 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. © 2021 John Wiley & Sons, Ltd.