Abstract
Fabricating Zn1−xMgxO films with a high Mg content is key to their applications in deep-ultraviolet optoelectronic devices. In this work, we report the preparation of Zn1−xMgxO films on (12̄10)-ZnO substrates by molecular beam epitaxy. The Zn1−xMgxO/(12̄10)-ZnO structure is revealed by x-ray diffraction and high-resolution transmission electron microscopy. Remarkably, no cubic MgO is observed for films with 74.6% Mg content; the film shows mainly the wurtzite structure with some intermediate phases at the interface. Photoluminescence spectra show that the film exhibits good optoelectronic properties with a bandgap of 4.6 eV. This work provides a new avenue for the fabrication of deep-ultraviolet Zn1−xMgxO films.
Highlights
Zn1−xMgxO alloy films have attracted much attention owing to their potential applications in deep-ultraviolet-emitting diodes and solar-blind photodetectors.1–3 These typical optoelectronic devices demand that the bandgap of Zn1−xMgxO is larger than 4.0 eV and that the Mg content is more than 33%.4,5 phase separation usually occurs for Zn1−xMgxO with a Mg content between 37% and 62%6,7 because the stable phase of MgO is cubic and the stable phase of ZnO is wurtzite
It can be clearly seen that the diffraction spot arrays of the film are almost the same as those of the substrate, as scitation.org/journal/adv shown by the red and blue arrows in the selected-area electron diffraction (SAED) pattern, indicating that the main phase structure of the alloy film is wurtzite, the same as that of the substrate
The concentric halo in the SAED diagram could be originated from the mixed phases
Summary
Zn1−xMgxO alloy films have attracted much attention owing to their potential applications in deep-ultraviolet-emitting diodes and solar-blind photodetectors. These typical optoelectronic devices demand that the bandgap of Zn1−xMgxO is larger than 4.0 eV (i.e., that the wavelength is less than 300 nm) and that the Mg content is more than 33%.4,5 phase separation usually occurs for Zn1−xMgxO with a Mg content between 37% and 62%6,7 because the stable phase of MgO is cubic and the stable phase of ZnO is wurtzite. Control of Zn1−xMgxO with a higher Mg content and a solar-blind region bandgap are important requirements for applications in deep-ultraviolet optoelectronic devices.9 To deal with this issue, great effort has been spent in exploring strategies for the preparation of Zn1−xMgxO alloy films. Redondo-Cubero et al. obtained the MgZnO film with the Mg content greater than 50% on sapphire without phase separation, with only wurtzite phase Another approach is to utilize a buffer layer to improve the solubility of Mg. For example, Schoenfeld et al. obtained high-quality single-phase Zn1−xMgxO with an Mg content of 46% on a (0001)-Al2O3 substrate via a ZnO buffer layer. This work opens a new route to Zn1−xMgxO with the increasing Mg content
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