Band Offsets in the Mg 0.5 Ca 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 2 O 3 . X-ray photoelectron spectroscopy (XPS) was used to measure the energy discontinuity in the valence band (Δ E v ) of Mg 0.5 Ca 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 Δ E 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 Δ E C of 3.36 eV in the Mg 0.5 Ca 0.5 O system.