MgxZn1-xO alloy films were deposited on c-plane sapphire substrates by radio frequency plasma-assisted molecular beam epitaxy (rf-PMBE). The phase segregation occurred when x was larger than 33%. Be doping was found experimentally able to stabilize the high-Mg-content MgZnO alloy. By alloying 1-2% Be into MgZnO, the band gap of as-prepared quaternary alloys can be raised to the solar-blind range (4.5 eV). Calculated formation energy of the alloys based on first principle reveals that a small amount of Be incorporation can reduce the formation energy of high-Mg-content MgZnO alloys and results in a more stable system, which justifies our experimental observations. © 2013 IOP Publishing Ltd.