Thin, crystalline MgO on hexagonal 6H-SiC(0001) by molecular beam epitaxy for functional oxide integration

Abstract

MgO thin films are proposed as a template for the effective integration of three and four element oxides on wide band gap SiC for next generation multifunctional devices. Oriented, crystalline MgO(111) of 20–380Å is grown on 6H-SiC(0001) by molecular beam epitaxy at a substrate temperature of 140°C using a magnesium effusion cell and a remote oxygen plasma source with ion deflection plates located at the end of the plasma discharge tube and approximately 7in. from the sample surface. Films are conformal to the steps of the cleaned SiC surface with a rms roughness of 0.45±0.05nm. Magnesium adsorption controls the growth rate in an excess oxygen environment with Mg:O flux ratios of 1:99–1:20, where the oxygen flux is the equivalent molecular oxygen. The oxygen plasma, which was determined to be free of ions when the ion deflection plates are energized, does impact nucleation and initial stages of the MgO film formation, and there may be evidence of etching mechanisms involved in the thicker film growth. Chemical and structural thermal stability of 20Å MgO(111)‖6H-SiC(0001) was demonstrated up to 740°C in vacuum for 90min through reflection high-energy electron diffraction and x-ray photoelectron spectroscopy analyses. X-ray diffraction was used to further test the thermal stability of 380Å films in vacuum and in an oxygen environment up to 790°C. As a proof of concept for MgO(111) as an interface for aligned functional oxide growth, barium titanate (111) was deposited on 100Å MgO(111)‖6H-SiC(0001) by rf magnetron sputtering.