MOS Ge Diodes Based on High $\kappa $ Gate Dielectrics Grown by MBE and ALD

Germanium-based CMOS technology is gaining importance due to its high carrier mobility. In this work high $\kappa $ gate-dielectrics, Al$_{2}$O$_{3}$, HfO$_{2}$, Y$_{2}$O$_{3}$ and Ga$_{2}$O$_{3}$(Gd$_{2}$O$_{3})$ grown by MBE and ALD were investigated as passivation layers on n type Ge(100). Thermal stability of the MOS diodes was examined after various anneals. Prior to dielectric depositions surface pretreatments were applied to reduce the unwanted GeO$_{x}$ interfacial layer, and to improve electrical properties. Frequency dispersion of C-V curves was reduced by using a 350$^{o}$C preclean process, compared to the sample without precleaning. The leakage current density of ALD grown HfO$_{2}$ (6.8nm) is 4.6×10$^{-6 }$A/cm$^{2}$ with $\kappa $ of 10.5. The improved CV curve was attributed to less GeO$_{x}$ formed at substrate and oxide interface, as confirmed by XPS analysis. However, with higher cleaning temperature over 400$^{o}$C, the CV curves showed additional inversion capacitance, possibly due to minority carriers from defect states near the interface.