Thermal stability of ultra-wide-bandgap MgZnO alloys with wurtzite structure

Abstract

Mg x Zn 1−x O thin films were grown as metastable alloys via a sputtering technique in order to achieve single-phase wurtzite alloys with deep-UV optical bandgaps. As-grown alloys with Mg composition range 0-72% resulted in optical bandgaps spanning the UV-range of 3.3-4.4 eV. The thermal stability of the alloys was studied via post-growth controlled annealing experiments up to 900 °C. Alloys with low Mg up to 34% were found to be highly stable and retained their optical and material properties; however, alloys with higher Mg, up to 72%, were found to be unstable and were phase separated into wurtzite and cubic structural phases with respective optical bandgaps at ~ 3.5 and 6.0 eV. Both the as-grown and annealed alloys were studied using X-ray diffraction for structural identification, transmission spectroscopy for bandgap analysis, and Raman scattering for mapping the phonon mode-behavior. The experimental value for the solubility limit was found to be ~ 30%. A straightforward model calculation based on the Raman-mode saturation behavior yielded a similar value for the solubility limit of the alloys. The results are discussed in terms of available phase-diagrams for stable-state ceramics alloys that were grown under thermodynamics equilibrium conditions.

Phonon-Polariton Excitations in MgZnO/6H-SiC Structures

“…It should be noted that, in some papers [29][30][31], it was reported about the fabrication of thin films of Mg Zn 1− O solid solutions with = 0.24-0.30 and the hexagonal structure. If was increased to 0.4, the cubic MgO phase was also formed.…”

MgZnO/SiO2/ZnO metal–semiconductor–metal dual-band UVA and UVB photodetector with different MgZnO thicknesses by RF magnetron sputter

“…On the other hand, the phase separation of MgZnO thin film did not occur for three fabricated PDs (not shown here), which in general can be found at a Mg composition of more than 50%. 31) Then, Fig. 4 shows the SEM images of MgZnO/SiO 2 /ZnO thin films for these fabricated PDs.…”

Electroluminescent MgZnO/ZnO Heterojunction Diode

“…A MgZnO layer with high Mg composition forms a high barrier height from a bandgap larger than that of ZnO, which is necessary to fabricate tunnel diodes. However, MgZnO with a Mg content above 25 % is challenging to obtain under equilibrium thermodynamic growth conditions [16]. Therefore, the MgZnO barrier layer with a high Mg content was deposited using RF sputtering.…”

“…In addition, MgZnO and CdZnO layers, adopted through bandgap engineering by alloying MgO and CdO, enable the fabrication of ZnO-based quantum heterostructures and heterojunction devices [12][13][14][15]. However, achieving a high Mg composition in ZnO-based alloy layers such as MgZnO, is challenging owing to the limited alloy solubility (25.0 and 8.5 % [16,17] for Mg and Cd, respectively). Moreover, the fabrication of MgZnO/ZnO heterostructured layers is limited owing to the difference in the crystalline structures of ZnO (wurtzite) and MgO (cubic), which makes it challenging to achieve epitaxial layer-by-layer growth between ZnO and MgZnO with a high Mg composition.…”