Open-volume (vacancy-type) point defects were observed in ~80nm-thick titanium dioxide films grown onto silicon dioxide/4H silicon carbide substrates as stacks with high dielectric constant for power device applications, using variable-energy positron annihilation spectroscopy. The concentration of vacancies decreased as the titanium dioxide growth temperature was increased in the range from 700 to 1000C, whereas grain boundaries form in the polycrystalline material at the highest growth temperatures. It was proposed that the optimal electrical performance for films grown at 800C reflects a balance between decreasing vacancy concentration and increasing grain boundary formation. The concentration of vacancies at the silicon dioxide/silicon carbide interface appeared to saturate after 2.5h oxidation at 1150C. A supplementary result suggests that the quality of the 10µm-thick deposited silicon carbide epilayer was compromised at depths of about 2µm and beyond, possibly by the migration of impurities and/or other defects from the standard-grade highly doped 4H silicon carbide wafer beneath the epilayer during oxidation.

Vacancy-Type Defects in TiO2/SiO2/SiC Dielectric Stacks. Coleman, P.G., Burrows, C.P., Mahapatra, R., Wright, N.G.: Journal of Applied Physics, 2007, 102[1], 014106