Determination of MgO/GaN heterojunction band offsets by x-ray photoelectron spectroscopy

MgO is a promising gate dielectric and surface passivation film for GaN transistors but little is known of the band offsets in the MgO/GaN system. X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band (Delta E-v) of MgO/GaN heterostructures in which the MgO was grown by rf plasma-assisted molecular beam epitaxy on top of thick GaN templates on sapphire substrates. A value of Delta E-v=1.06 +/- 0.15 eV was obtained by using the Ga 3d energy level as a reference. Given the experimental band gap of 7.8 eV for the MgO, this would indicate a conduction band offset Delta E-C of 3.30 eV in this system. (c) 2006 American Institute of Physics.