Effects of Mg doping concentration on the band gap of ZnO/Mg x Zn1?x O multilayer thin films prepared using pulsed laser deposition method

摘要

Epitaxial ZnO/Mg x Zn1-x O 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/Mg x Zn1-x O multilayer thin films were grown by stacking alternate layers of ZnO and Mg x Zn1?x O 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 Mg x Zn1?x O 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[ {10bar 11} right]_{{text{multilayer}}} } right|left( {0001} right)left[ {10bar 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/Mg x Zn1?x O multilayer thin films. The 2θ value of Mg x Zn1?x O (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.