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 (ΔEv) 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 ΔEv=1.06±0.15eV was obtained by using the Ga 3d energy level as a reference. Given the experimental band gap of 7.8eV for the MgO, this would indicate a conduction band offset ΔEC of 3.30eV in this system.

The Sc2O3∕GaN interface shows low trap densities and has been used both to demonstrate inversion in gated metal-oxide-semiconductor diodes and to mitigate current collapse in AlGaN∕GaN heterostructure transistors but little is known of the band offsets at this interface. We measured the energy discontinuity in the valence band (ΔEv) of Sc2O3∕GaN heterostructures using x-ray photoelectron spectroscopy. A value of ΔEv=0.42±0.07eV was obtained using the Ga 3d energy level as a reference. With the experimental band gap of 6.0eV for the Sc2O3 grown by this method, this implies that the conduction band offset ΔEC is 2.14eV in this system.

Ti ∕ Au Ohmic contacts on heavily Al-doped (n∼1019cm−3) n-ZnO produce low specific contact resistivity of 2.4×10−7Ωcm2 in the as-deposited condition and extremely low minimum values of 6×10−8Ωcm2 after annealing at 300°C.The contact resistance is independent of measurement temperature after low temperature anneals, suggesting that tunneling is the dominant transport mechanism in the contacts. The contact morphology roughens after annealing at 150°C and Auger electron spectroscopy depth profiling shows Zn outdiffusion through the metal and intermixing of Au and Ti. However, the morphology does not significantly worsen after anneals at 450°C. This metallization scheme looks very attractive for the n-electrode of ZnO-based light-emitting diode structures.

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 (DE 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 DE 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 DE C of 3.36 eV in the Mg 0.5 Ca 0.5 O system.

metallization schemes was investigated using x-ray photoelectron spectroscopy (XPS), current-voltage (I-V), and Auger electron spectroscopy measurements. The Schottky barrier height (SBH) determined from XPS is 2.71 eV and 2.87 eV for as-deposited W 2 B-and W 2 B 5 -based contacts, respectively. By comparison, fitting of the I-V curves using the thermionic field emission model gives unphysical SBHs > 4 eV due to the presence of an interfacial layer acting as an additional barrier to carrier transport. Upon annealing to~600-700°C, the diodes show slight deterioration in rectifying behavior due to the onset of metallurgical reactions with the GaN. The experimental dependence of the reverse leakage current on bias and measurement temperature is inconsistent with both thermionic emission and thermionic field emission models, suggesting that leakage must originate from other mechanisms such as surface leakage or generation in the depletion layer through deep-level defects.