Structural and optical properties of hexagonal MgxZn1-xO thin films

High-quality epitaxial magnesium zinc oxide (MgxZn1-xO) alloy thin films were grown on sapphire (alpha-Al2O3 (0001)) substrates using pulsed laser deposition. The structural and optical properties of these hexagonal films were determined using transmission electron microscopy (TEM), x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), absorption, and photoluminescence measurements. XRD and TEM data reveal that magnesium zinc oxide alloy films, grown by domain matching epitaxy, exhibited the following relationships: MgZnO[0001] parallel to alpha-Al2O3 [0001] and MgZnO[0110] parallel to alpha-Al2O3 [2 (1) over bar(1) over bar0]. RBS data demonstrate that a maximum magnesium content of x = 0.34 can be obtained in hexagonal ZnxMg1-xO thin films. This value is significantly higher than the thermodynamic limitation of x = 0.04. The absorption spectra of magnesium zinc oxide alloy films obtained at room temperature demonstrate significant excitonic behavior. The exciton binding energies have been extracted from the absorption data. Values of the exciton bandgap as a function of magnesium content were determined by fitting the bandgap energies using polynomial fitting. The ZnxMg1-xO alloy thin films demonstrate bright room-temperature luminescence and significant excitonic behavior. A shift in the excitonic emission peak as a function of magnesium content was observed.