Characterisation and growth of polar MgO(111) thin films prepared by Molecular Beam Epitaxy

Magnesium oxide MgO has developed research interest for its use in electronic and spin electronic device applications. Examples of these devices are power MOSFETs and spinFETs. Power MOSFET devices have been developed with silica gates on SiC substrates, however dielectric properties of silica and extreme operating and processing conditions of SiC based devices present problems with electrical properties of such devices. The dielectric properties of MgO make it an ideal replacement for silica in power MOSFET devices with Silicon Carbide. These properties in combination with high tunneling magneto resistances recorded for magnetic tunneling junctions using MgO suggest that MgO/SiC hetero-junctions could also be applicable to the field of semiconductor spintronics and spinFET devices.

The polar structure of MgO has been of research interest for many years. The aims of this work are to understand the electronic structure at the interface for prospective device applications and to understand the impact of the polar structure on MBE grown MgO(111) thin films.

The results presented in this work show successful growth of polar MgO(111) thin films prepared by MBE confirmed by analysis of the thin films using surface electron diffraction, XPS, TEM and STEM techniques. Preparation of flat 6h-SiC(0001) by hydrogen cleaning in UHV is demonstrated herein, resulting in a clean template for subsequent MgO(111) growth.

Successful growth of MgO(111) films as thin as a few nanometres has also been demonstrated. Structural characterisation of these films has been performed using RHEED and STEM and the electronic band alignment at the interface of MgO thin films with 6h-SiC(0001) has also been measured by XPS. This work also resolves discrepancies in the valence band offset reported in the literature, which have been clarified using STEM and CASTEP simulations.