Molecular beam epitaxy of MgxZn1-xO layers without wurzite-rocksalt phase mixing from x=0 to 1 as an effect of ZnO buffer layer

MgchiZn1-chiO (0 less than or equal to chi less than or equal to 1) layers without wurzite-rocksalt phase mixing have been successfully grown by MBE on a-plane sapphire substrates with ZnO buffer layers. The layers of chi < 0.5 take wurzite (0001) structure eliminating the problem of wurzite-rocksalt phase mixing reported previously between chi = 0.35 and 0,45, while those of chi > 0.5 rocksalt (001) with wurzite (0001) structure only at the initial stage of the growth (<25 nm). The rocksalt (001) rather than (111) which has been generally seen on sapphire without ZnO buffer layers can be explained by the model showing successive transition from wurzite (0001) to rocksalt (001) with the tensile and compressive deformation of the lattices along a- and b-axes, respectively. The band gap energy of MgchiZn1-chiO has been continuously tuned without the problem of unstable phase mixing. (C) 2004 WILEY-VCH Vertag GmbH & Co. KGaA. Weinheim.