Effects of Mg doping concentration on the band gap of ZnO/MgxZn1−xO multilayer thin films prepared using pulsed laser deposition method

Epitaxial ZnO/MgxZn1-xO multilayer thin films (x = 0~0.15) were prepared on c-Al2O3 substrates by pulsed laser deposition and their crystallinity and optical properties were investigated using X-ray diffraction, TEM, and UV-Vis spectroscopy. ZnO/MgxZn1-xO multilayer thin films were grown by stacking alternate layers of ZnO and MgxZn1−xO with laser fluence of 3 J/cm2, repetition rate of 5 Hz, substrate temperature of 600 °C, and oxygen partial pressure of 5 × 10–4 Torr. The thickness of individual ZnO and MgxZn1−xO layers was maintained at 3 and 6 nm, respectively, and the total thickness of the films was kept in 300 nm. X-ray diffraction results showed that the multilayer thin films were grown epitaxially on c-Al2O3 substrates with an epitaxial orientation relationship of \(\left. {\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{multilayer}}} } \right\|\left( {0001} \right)\left[ {10\bar 11} \right]_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} } \). Cross-sectional TEM micrographs showed alternating layers of bright and dark contrast, indicating the formation of ZnO/MgxZn1−xO multilayer thin films. The 2θ value of MgxZn1−xO (0002) peak increased from 34.30° at x = 0 to 34.67° at x = 0.15 with increasing Mg doping concentration in the multilayer thin films. The absorption edge in the UV-Vis spectra shifted to shorter wavelength from 360 at x = 0 to 342 nm at x = 0.15 and the band gap energy increased from 3.27 eV at x = 0 to 3.54 eV at x = 0.15.