High-k perovskite gate oxide for modulation beyond 10¹⁴ cm^-2

Scaling down of semiconductor devices requires high-k dielectric materials to continue lowering the operating voltage of field-effect transistors (FETs) and storing sufficient charge on a smaller area. Here, we investigate the dielectric properties of epitaxial BaHf_0.6Ti_0.4O₃ (BHTO), an alloy of perovskite oxide barium hafnate (BaHfO₃) and barium titanate (BaTiO₃). We found the dielectric constant, the breakdown field, and the leakage current to be 150, 5.0 megavolts per centimeter (MV cm^-1), and 10^-4 amperes per square centimeter at 2 MV cm^-1, respectively. The results suggest that two-dimensional (2D) carrier density of more than n_2D = 10¹⁴ per square centimeter (cm^-2) could be modulated by the BHTO gate oxide. We demonstrate an n-type accumulation mode FET and direct suppression of more than n_2D = 10¹⁴ cm^-2 via an n-type depletion-mode FET. We attribute the large dielectric constant, high breakdown field, and low leakage current of BHTO to the nanometer scale stoichiometric modulation of hafnium and titanium.