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GaN surface and near-surface chemistry influence on band offsets of oxide overlayers is demonstrated through X-ray photoelectron spectroscopy measurements using epitaxial (111)-oriented MgO films on (0001)-oriented Ga-polar GaN as a case study. For identical cleaning and MgO growth conditions, GaN subsurface oxygen impurities influence the GaN bare surface band bending and the ultimate band offset to MgO heterolayers. As the GaN surface oxygen concentration increases from an atomic concentration of 0.9% to 3.4%, the valence band offset to MgO decreases from 1.68 eV to 1.29 eV, respectively. This study highlights the sensitivity of the oxide/nitride interface electronic structure to GaN epilayer preparation and growth conditions.

Epitaxial (111) MgO films were prepared on (0001) AlxGa1−xN via molecular-beam epitaxy for x = 0 to x = 0.67. Valence band offsets of MgO to AlxGa1−xN were measured using X-ray photoelectron spectroscopy as 1.65 ± 0.07 eV, 1.36 ± 0.05 eV, and 1.05 ± 0.09 eV for x = 0, 0.28, and 0.67, respectively. This yielded conduction band offsets of 2.75 eV, 2.39 eV, and 1.63 eV for x = 0, 0.28, and 0.67, respectively. All band offsets measured between MgO and AlxGa1−xN provide a > 1 eV barrier height to the semiconductor.

Gd2O3 films were prepared on (0001)-oriented AlxGa1−xN (0 ≤ x ≤ 0.67) thin film substrates via reactive molecular-beam epitaxy. X-ray diffraction revealed that these films possessed the cubic bixbyite structure regardless of substrate composition and were all 111-oriented with in-plane rotations to account for the symmetry difference between the oxide film and nitride epilayer. Valence band offsets were characterized by X-ray photoelectron spectroscopy and were determined to be 0.41 ± 0.02 eV, 0.17 ± 0.02 eV, and 0.06 ± 0.03 eV at the Gd2O3/AlxGa1−xN interfaces for x = 0, 0.28, and 0.67, respectively.

La2O3 films were prepared on (0001)-oriented GaN substrates via reactive molecular-beam epitaxy. Film orientation and phase were assessed using reflection high-energy electron and X-ray diffraction. Films were observed to grow as predominantly hexagonal La2O3 for thicknesses less than 10 nm while film thickness greater than 10 nm favored mixed cubic and hexagonal symmetries. Band offsets were characterized by X-ray photoelectron spectroscopy on hexagonally symmetric films and valence band offsets of 0.63 ± 0.04 eV at the La2O3/GaN interface were measured. A conduction band offset of approximately 1.5 eV could be inferred from the measured valence band offset.

A technique for characterizing trapped charge in silicon carbide (SiC) metal oxide semiconductor field effect transistors (MOSFETs) based only on the subthreshold I-V characteristics and its degradation under bias temperature stress is described. The method utilizes the large departure of the subthreshold slope from a constant value, due to large and exponentially rising DIT (density of interface traps) near band edges for SiC/SiO2 interface. Elevated bias-temperature stress experiments demonstrate the feasibility of separating ΔNIT (increase in interface trapped charge) from slow trapping components like ΔNOT (increase in oxide trapped charge) with minimal error due to extrapolation of subthreshold current to midgap potentials. A slow trap, dissimilar to either interface or oxide states close to the interface, dominates degradation at elevated temperature.