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

Highlights: • Four sets (0 0 0 2)-oriented nano-domains are embedded in a-plane ZnO MQWs. • Nano-domains with ZnMgO buffer reveal additional linear polarizations orientation. • Phase-contrast AFM can correlate ND's boundary and interface-bound exciton emission. The anisotropic exciton emission in a-plane nonpolar ZnO/ZnMgO MQWs offers opportunity for anisotropic photonic devices. By introducing Zn_1-yMg_yO buffer layer between r-plane sapphire substrate and MQWs, we investigated the structural and optical properties of ten-period a-plane ZnO/Zn_1−xMg_xO (ZnO/ZnMgO) multiple quantum wells (MQWs) with different widths of Zn_1−xMg_xO barrier layers grown by pulsed-laser deposition on Zn_1-yMg_yO 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 $\overline{2}$ 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.