A route for synthesizing high Mg content single-phase wurtzite MgZnO films having band gaps in the solar-blind region is demonstrated by employing molecular beam epitaxy on Al 2 O 3 substrates. Importantly, a low Mg content “quasi-homo” buffer, Mg 0.17 Zn 0.83 O, was applied to accommodate a host of structural discrepancies and therefore, avoiding phase separation in a high Mg content film, Mg 0.55 Zn 0.45 O, as proved by X-ray diffraction. The Mg fraction in the overgrown single-phase epilayer, Mg 0.55 Zn 0.45 O, was confirmed by Rutherford backscattering spectrometry.