Abstract We demonstrate the growth of Be _x Zn_1−x O alloy thin films on c-sapphire substrates by plasma-assisted molecular beam epitaxy. The formation of Be _x Zn_1−x O is very sensitive to the Be content in the alloy. Be atoms occupy the Zn lattice sites at low Be content, but move partly to the interstitial sites with increasing Be content. We also investigated the thermal stability of N, one of the most frequently used p-type dopants, in the Be _x Zn_1−x O films. Secondary ion mass spectrometry shows that Be element plays a crucial role in stabilizing N in the Be _x Zn_1−x O host, which is favourable in improving the solid solubility and the thermal stability of acceptor dopants in ZnO-based wide-gap semiconductors.