Ultrathin HfO2 (equivalent oxide thickness=1.1nm) metal-oxide-semiconductor capacitors on n-GaAs substrate with germanium passivation

We present the capacitance-voltage characteristics of TaN∕HfO2∕n-GaAs metaloxide-semiconductor capacitors, with an equivalent oxide thickness (EOT) of 10.9A, low frequency dispersion, and a low leakage current density (Jg) of ∼10−6A∕cm2 at ∣VG−VFB∣=1V. Physical vapor deposited high-k dielectric film (HfO2) and a thin germanium (Ge) interfacial control layer (ICL) were used to achieve the low EOTs. As postdeposition annealing (PDA) time increases beyond a critical point, EOT and Jg also abnormally increase due to the degradation of the interface between Ge and GaAs surface, which was well indicated in electron energy loss spectroscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy analyses. Results indicate that a thin Ge ICL, optimized conditions for PDA, as well as high-k material (HfO2) play important roles in allowing further EOT scale down and in providing a high-quality interface.