Structural analysis of the ZnO/MgO superlattices on a-polar ZnO substrates grown by MBE

Abstract

The analysis of heteroepitaxially grown ZnO/MgO superlattices on a-oriented ZnO substrates was described. The influence of unalike natural crystalline structures of ZnO and MgO on the interface's abruptness and retaining wurtzite crystallinity was studied. Wurtzite structure was found to be retained in the MgO thin barriers up to 1.5 nm, but creation of nonuniform biaxial strains and some interdiffusion of Mg from barriers to ZnO QW's seemed to be inevitable. The complex strain/composition heterogeneities can be explained by the difference of vapor pressure between Mg (p = 1.93 Pa) and Zn (p = 0.22 Pa) elements at growth temperatures and high mobility of Mg atoms, which are gladly incorporated into ZnO matrix. As a result, a subtle three monolayers in size ZnMgO film was created at the interfaces, which was partly responsible for retaining the wurtzite structure of coherently grown MgO layers.