Growth of MgO thin films on M-, A-, C- and R-plane sapphire by laser ablation

Epitaxial MgO thin films have been grown on single crystal substrates of M-plane (100), A-plane (20), C-plane (0001) and R-plane (102) sapphire by laser ablation of a Mg metal target in a molecular oxygen atmosphere using 1064 nm radiation from a Nd:YAG laser. X-ray measurements indicate that the MgO grows epitaxially on all substrates, with its orientation dependent on the cut of the sapphire substrate. (110)-oriented MgO grows on M-plane sapphire, while (111)-oriented MgO films are found on both the A-plane and the C-plane sapphire. The orientation of MgO found on R-plane sapphire appears to be surface and temperature dependent. The principal growth orientation obtained on the R-plane is (100)-oriented MgO although (100) growth tilted 30° from the [11] Al₂O₃ direction can result. X-ray area mapping has been performed to determine the mosaicity, d value spread and strain present in the films. These data are compared with the in-plane orientation and the mismatch of the MgO and Al₂O₃ lattices in an attempt to relate the preferred orientation to the plane of the sapphire on which it is grown.