Optical and structural properties of epitaxial MgxZn1−xO alloys

Abstract

The optical and structural properties of high-quality single-crystal epitaxial MgZnO films deposited by pulsed-laser deposition were studied. In films with up to ∼36 at. % Mg incorporation, we have observed intense ultraviolet band edge photoluminescence at room temperature and 77 K. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy was used to show that the excitonic structure of the alloys was clearly visible at room temperature. High-resolution transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy/ion channeling were used to verify the epitaxial single-crystal quality of the films and characterize the defect content. Post-deposition annealing in oxygen was found to reduce the number of defects and to improve the optical properties of the films. These results indicate that MgZnO alloys have potential applications in a variety of optoelectronic devices.

Lattice parameters and electronic structure of BeMgZnO quaternary solid solutions: Experiment and theory

“…However, bandgaps achievable in MgZnO and BeZnO ternaries are restricted by limited solubility of BeO and MgO in wurtzite ZnO lattice. As MgO is stable in the rocksalt phase (7.7 eV bandgap), phase segregation in MgZnO is inevitable and has been reported for Mg concentrations above 33% (corresponding wurtzite MgZnO bandgap of $4.0 eV) for films grown at substrate temperatures of !600 C. 3,4 Higher Mg contents up to 55% (corresponding wurtzite MgZnO bandgap of $4.5 eV) could be achieved at much lower growth temperatures of 250 C at the expense of significantly degraded material quality and tendency toward phase segregation at elevated temperatures. 5 On the other hand, in the case of BeZnO ternary (BeO having the wurtzite structure with 10.6 eV bandgap), the phase segregation is primarily driven by the large difference in covalent radii (1.22 Å for Zn and 0.96 Å for Be 6 ) and has been observed for Be contents as low as 10%, [7][8][9] despite the relatively low growth temperatures used (400-500 C).…”

Structural phase transitions and fundamental band gaps ofMgxZn1−xOalloys from first principles

“…The solubility depends strongly on experimental conditions and can be considerably increased at high temperatures and high pressures. 5,6 Non-equilibrium growth processes, like pulsed laser deposition (PLD) 7,8,9,10,11 and molecular beam epitaxial methods 12,13,14,15 , allow to grow highquality Mg x Zn 1−x O thin films for a large range of concentrations x. For RS-Mg x Zn 1−x O, produced by PLD, a maximum solubility has been reported for x = 0.5.…”

Single phase a-plane MgZnO epilayers for UV optoelectronics: substitutional behaviour of Mg at large contents

“…Remarkably, these valúes are cióse to those already reported on c-plane MgZnO films (with Xmin ~ 5%). 20 As shown in Fig. 1, the good quality of the layers is also preserved with depth, and a significant rise of x min is only visible for ions reaching the buffer layer (energies between 1500 and 1700 keV).…”