Epitaxially grown crystalline Al2O3 interlayer on β-Ga2O3(010) and its suppressed interface state density

Abstract

Al2O3 films were deposited on β-Ga2O3(010) and β-Ga2O3(201) substrates by atomic layer deposition at 250 °C, and their interface state densities (Dit) at shallow energies were evaluated using a high-low capacitance-voltage (C-V) method. Al2O3/β-Ga2O3(010) showed lower Dit values (5.9 × 1010 to 9.3 × 1011 cm-2 eV-1) than Al2O3/β-Ga2O3(201) (2.0 × 1011 to 2.0 × 1012 cm-2 eV-1) in an energy range of %0.8 to %0.1 eV. Crosssectional transmission electron microscopy analysis indicated the formation of a uniform amorphous Al2O3 layer on the β-Ga2O3(201) substrate. In contrast, a crystalline Al2O3 interlayer with a thickness of 3.2 + 0.7 nm with an amorphous Al2O3 top layer was formed on the β-Ga2O3(010) substrate, which effectively decreased Dit. Moreover, thicker interlayers showing lower Dit values at deep state levels were formed at deposition temperatures higher than 100 °C, which were evaluated by shifts in the C-V curves.