Acoustic waves in (0 0 1) anisotropic polytype heterostructures

We have studied the acoustic waves of (0 0 1) polytype heterostructures formed by slabs of cubic crystals. We have considered symmetric and asymmetric heterostructures formed by AlN, GaN and InN in the zinc-blende structure due to the potential applications of these materials. The anisotropy of the materials has been taken into account and the different propagation directions ranging from the [1 0 0] to the [1 1 0] have been considered. We obtain the dispersion relations for different propagation directions. The coupling between the spatial components of the elastic displacements is different for symmetry and general propagation directions. The spatial localization of the modes in the heterostructures has also been obtained.     

Acoustic waves in (001) InN–AlN and InN–GaN superlattices

We study the acoustic waves of (001) InN–AlN and InN–GaN superlattices. We obtain the dispersion curves for various symmetric and general orientations of the wavevector parallel to the interfaces. The results reveal the impact of the elastic anisotropy due to the zinc-blende structure of the constituent materials. It is found that for certain material parameters and orientations, the dispersion curves exhibit wide gaps with potential for the existence of surface localized waves.     

Optical transmission properties of an anisotropic defect cavity in one-dimensional photonic crystal

We investigate theoretically the possibility to control the optical transmission in the visible and infrared regions by a defective one dimensional photonic crystal formed by a combination of a finite isotropic superlattice and an anisotropic defect layer. The Green's function approach has been used to derive the reflection and the transmission coefficients, as well as the densities of states of the optical modes. We evaluate the delay times of the localized modes and we compare their behavior with the total densities of states. We show that the birefringence of an anisotropic defect layer has a significant impact on the behavior of the optical modes in the electromagnetic forbidden bands of the structure. The amplitudes of the defect modes in the transmission and the delay time spectrum, depend strongly on the position of the cavity layer within the photonic crystal. The anisotropic defect layer induces transmission zeros in one of the two components of the transmission as a consequence of a destructive interference of the two polarized waves within this layer, giving rise to negative delay times for some wavelengths in the visible and infrared light ranges. This property is a typical characteristic of the anisotropic photonic layer and is without analogue in their counterpart isotropic defect layers. This structure offers several possibilities for controlling the frequencies, transmitted intensities and the delay times of the optical modes in the visible and infrared regions. It can be a good candidate for realizing high-precision optical filters.