Electrical properties of Al2O3/4H-SiC structures grown by atomic layer chemical vapor deposition

Al2O3 films have been deposited on n-type and p-type 4H-SiC by atomic layer chemical vapor deposition using trimethylaluminum as a precursor for aluminum and both H2O and O3 as an oxidant. After oxide deposition, annealing at different temperatures (800, 900, 1000 °C) in argon atmosphere for different durations (1, 2, 3 h) was performed. Bulk and interface properties of the oxide films were studied by capacitance-voltage, current-voltage, deep level transient spectroscopy, and thermally dielectric relaxation current (TDRC) measurements. The results reveal a decreasing flatband voltage with increasing annealing time, suggesting decrease of oxide charges and deep interface traps. After 3 h annealing at 1000 °C of the n-type samples, the flatband voltage is reduced to 6 V compared to a value in excess of 40 V for as-deposited samples. The TDRC measurements on annealed Al2O3/SiC (n-type) capacitors showed substantially different spectra relative to conventional SiO2/4H-SiC control samples; in the former ones no signal was recorded at temperatures less than 100 K, demonstrating a low density of shallow electron traps below the conduction band edge of 4H-SiC and hence a prospect of obtaining a high electron channel mobility in 4H-SiC metal-oxide-semiconductor field-effect devices with Al2O3 as gate dielectric.