The effect of Mg_0.1Zn_0.9O layer thickness on optical band gap of ZnO/Mg_0.1Zn_0.9O nano-scale multilayer thin films prepared by pulsed laser deposition method

Epitaxial ZnO/Mg_0.1Zn_0.9O (MZO) nano-scale multilayer thin films were prepared on Al₂O₃ (0001) substrates by pulsed laser deposition. The ZnO/MZO multilayer thin films were grown by stacking alternate layers of ZnO and Mg_0.1Zn_0.9O with a laser fluence, repetition rate, substrate temperature and oxygen partial pressure of 3 J/cm², 5 Hz, 600 °C and 3.8 × 10 ^{- 7} Pa, respectively. The thickness of an individual ZnO layer was maintained at 3 nm, whereas that of the MZO layers was varied from 3 nm to 15 nm. Cross-sectional transmission electron microscopy revealed alternating layers of bright and dark contrast, indicating the formation of a ZnO/MZO multilayer. X-ray diffraction results showed that multilayer thin films were epitaxially grown as a hexagonal wurzite phase with orientation relationship of (0001)[ _{101̄1]multilayer}||(0001)[_{101̄1]substrate}. The 2θ value of the (0002) peak of the ZnO/MZO multilayer thin films increased from 34.30° to 34.71°, indicating that Mg is replaced with Zn in the hexagonal lattice in the MZO of ZnO/MZO multilayer. UV-visible spectroscopy showed a systematic increase in the band gap of the ZnO/MZO multilayer thin films from 3.34 eV to 3.70 eV with increasing MZO layer thickness, which suggests that the band gap energy of a ZnO/MZO multilayer thin film can be controlled by varying the thickness of each constituent layer.