Analyses of Yttrium Oxide and Yttrium–doped Germanium Oxide on Germanium by Oxide MBE

In the dissertation, the oxide MBE system was harnessed to synthesize both yttrium oxide（Y_2 O_3）and yttrium – doped germanium oxide（Y - GeO_2）on germanium substrate. Then, the metal – oxide – semiconductor capacitor, MOSCap, devices were fabricated after metal was deposited on the semiconductor – oxide samples by utilizing the e – gun evaporator. The primary purpose was to determine whether the interfacial layer was necessary between Ge substrates and high – k materials as a buffer layer in Ge – based MOSCap devices. Additionally, due to the instable properties of GeO_2, yttrium atoms were doped into GeO_2 to strengthen the chemical bonding and ameliorate the overall performances of MOSCap devices, including higher dielectric constant（k）and lower leakage current density, etc. Using post – metallization annealing, PMA, was beneficial to improve the electrical characteristics in numerous aspects. Both border traps and interface – trap density（D_it）were observed to be lower after going through the process of PMA. The former could be clarified by the reduction of hysteresis and frequency dispersion in C – V measurement, the latter was confirmed by the calculation of high – low – frequency capacitance method. Furthermore, leakage current density of the devices was found to be lower in the PMA condition of 250 ℃. The explanation of the phenomenon was the repair of dangling bonds in oxide by hydrogen atoms in forming gas. In room temperature, the minimum value of interface – trap density of devices was 9.099 × 〖10〗^11 eV^(-1) cm^(-2) by utilizing the high – low – frequency capacitance method. At last, by comparing the interface – trap density of devices fabricated by a series of emission current, we concluded that the interfacial layer was needed between Ge substrates and high – k materials as a buffer layer due to lower D_it, indicating better interface quality than direct contact of Ge substrates and high – k materials.