Band Offsets in the Mg^sub 0.5^Ca^sub 0.5^O/GaN Heterostructure System

MgCaO offers promise as a gate dielectric for GaN-based metal-oxide-semiconductor (MOS) transistors, particularly in combination with environmentally stable capping layers such as Sc^sub 2^O^sub 3^. X-ray photoelectron spectroscopy (XPS) was used to measure the energy discontinuity in the valence band (ΔE^sub v^) of Mg^sub 0.5^Ca^sub 0.5^O/GaN heterostructures in which the MgCaO was grown by rf plasma-assisted molecular beam epitaxy on top of thick GaN templates on sapphire substrates. A value of ΔE^sub v^ = 0.65 eV ± 0.10 eV was obtained by using the Ga 3d energy level as a reference. Given the bandgap of 7.45 eV for the MgCaO, we infer a conduction band offset ΔE^sub C^ of 3.36 eV in the Mg^sub 0.5^Ca^sub 0.5^O system. [PUBLICATION ABSTRACT]