Simulated Interface Induced Raman Scattering Profiles of Optical Modes in Novel BeO/ZnO Superlattices

Despite recent intensified research efforts in novel alkaline earth oxides (AEOs), there still exist very few studies on their basic structural, optical and phonon characteristics. Exceptional combination of AEOs’ material traits including high thermal conductivity, electrical insulation, wide bandgap, spontaneous polarization at graded interfaces, have made BeO/ZnO strained layer superlattices (SLs) valuable for developing different electro-optical devices. These prospects offered opportunities to integrate SLs into flexible transparent high-performance transistors, ultraviolet light-emitting diodes, biosensors, nano-electronic and nanophotonic modules, etc. Such units are playing vital roles in thermal management solutions to provide safety for nuclear reactors and many medical equipment. In the absence of experimental data on phonon dispersions, dynamic displacements and Raman intensity profiles, systematic simulations are required. Using both elastic continuum and modified linear chain models, we have studied phonon characteristics of short-period BeO/ZnO SLs. Bond-polarizability method is adopted to calculate Raman scattering spectra of graded (BeO)10-D/(Be0.5ZnO0.5O)D/(ZnO)10-D/(Be0.5ZnO0.5O)D SLs by varying interfacial layer thickness from D ≡ 0 to 3 monolayers. The study has showed acoustic phonon branches of SLs weakly affected by interfacing. Low frequency optical modes are shifted upwards in frequency while the high frequency phonons exhibited downward changes up to ~171 cm-1. Increasing D has collectively caused the phonon modes to collapse in the middle of the optical phonon mode region. This has triggered perceiving many prominent Raman scattering features. Such effects are linked to the localization of atomic displacements. Our methodical study markedly insinuated that the Raman intensity profiles of optical modes in strained layer SLs can be well suited for probing the thickness of interfacial layer D, when epitaxially grown samples will become available.