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 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 (2.0 × 1011 to 2.0 × 1012 cm−2 eV−1) in an energy range of −0.8 to −0.1 eV. Cross-sectional transmission electron microscopy analysis indicated the formation of a uniform amorphous Al2O3 layer on the β-Ga2O3 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.