Optical anisotropy of interface-bound exciton emission in a-plane ZnO/Zn1-xMgxO MQWs with Zn1-yMgyO buffer layer

Abstract

The anisotropic exciton emission in a-plane nonpolar ZnO/ZnMgO MQWs offers opportunity for anisotropic photonic devices. By introducing Zn1-yMgyO buffer layer between r-plane sapphire substrate and MQWs, we investigated the structural and optical properties of ten-period a-plane ZnO/Zn1−xMgxO (ZnO/ZnMgO) multiple quantum wells (MQWs) with different widths of Zn1−xMgxO barrier layers grown by pulsed-laser deposition on Zn1-yMgyO buffered r-plane sapphire. Polarization-dependent photoluminescence spectra reveal that two additional linear polarizations of interface-bound exciton emission with E⊥c orienting at ~± 50° with respect to the regular a-plane MQWs are attributed to the generation of (0 0 0 2)-oriented nano-domains (NDs). As evidenced by XRD and TEM, we found four sets of (0 0 0 2)-oriented MQWs NDs are embedded in regular a-plane ZnO/ZnMgO MQWs with 90° in-plane rotation from one another which are inclined by 27.6° towards the [1 1 2¯ 0]-direction of the ZnO/ZnMgO MQWs. The existence of (0 0 0 2)-oriented NDs is further confirmed by the phase-contrast atomic force microscopy that modulates the optical anisotropy of interface-bound exciton emission in a-plane nonpolar ZnO/ZnMgO MQWs.