Growth of Scandium Magnesium Oxide on GaN

Abstract

Sc₂O₃ and MgO have been previously shown to be promising gate dielectrics for III-nitride devices. However, even though the films are initially epitaxial, they possess large numbers of defects due to the large mismatch with GaN. Thus further improvements in interface electrical characteristics will require a reduction in the interfacial mismatch between the oxides and the GaN. This paper discusses the feasibility of reducing the Sc₂O₃ lattice constant via the introduction of Mg and in particular investigates the relationship between growth parameters and microstructure for the resulting ScMgO alloy. Increasing the magnesium cell temperature was found to increase the growth rate but have little effect on surface roughness. Higher Mg cell temperatures also produced evidence in x-ray diffraction (XRD) of a second phase of MgScO which has the rock salt crystal structure and contains ∼2%Sc. Increasing the substrate temperature from 100°C to 300°C was found to have little effect on the growth rate and dramatically increased surface roughness. However higher substrate temperature combined with a lower Mg cell temperature produced a more uniform oxygen profile as determined by depth profiling Auger Electron Spectroscopy (AES). From AES and XRD, the solid solubility limit for Sc_xMg_1−xO with the Bixbyite structure was reached at about X_Mg =0.28