Plasma-assisted molecular-beam epitaxy of ZnO epilayers on atomically flat MgAl2O4(111) substrates

Plasma-assisted molecular-beam epitaxy of ZnO epilayers on ${\mathrm{MgAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}\text{(111)}$ substrates is described. Acid mixed by ${\mathrm{H}}_{\mathrm{2}}{\mathrm{SO}}_{\mathrm{4}}$ and ${\mathrm{H}}_{\mathrm{3}}{\mathrm{PO}}_{\mathrm{4}}$ was used for the substrate etching, which provides atomically flat surfaces with a regular terrace array. The influence of the substrate on lateral growth and coalescence of ZnO islands during epitaxy is discussed with corresponding morphological and structural properties. The epitaxial relationship between the ZnO epilayer and ${\mathrm{MgAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}$ substrate is determined as: ${\mathrm{ZnO[011̄0]\parallel MgAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}\mathrm{[1̄1̄2]}$ and ${\mathrm{ZnO[21̄1̄0]\parallel MgAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}\mathrm{[1̄10]}.$ X-ray diffraction, photoluminescence, and Hall-effect measurements are reported, which indicate that high-quality ZnO epilayers are obtained by using atomically flat ${\mathrm{MgAl}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{4}}\text{(111)}$ substrates to suppress columnar growth.