Molecular beam epitaxy (MBE) was employed to grow nanothick high kappa HfO2 films on Si (100) as templates to suppress the formation of the oxide/Si interfacial layer during the subsequent atomic layer deposited (ALD) HfO2 growth. A metal-oxide-semiconductor (MOS) diode with the ALD/MBE bilayer stack of an equivalent oxide thickness (EOT) of similar to 1.1 nm has demonstrated markedly low electrical leakage of 8.3x10(-3) A/cm(2) at V-fb-1 V, a reduction by five order of magnitudes, comparing with those using SiO2 of the same EOT. The attainment of high dielectric constant and very small frequency dispersion in capacitance-voltage (C-V) curves suggests the absence of low kappa capacitors in series near the oxide/Si interface. Furthermore, MOS field-effect transistors (MOSFETs) based on the ALD/MBE-HfO2 composites have been fabricated having excellent device performance, with a drain current (I-D) of 240 mA/mm and transconductance (G(m)) of 120 mS/mm. These are superior to those of the MOSFETs using either ALD (55 mA/mm, 60 mS/mm) or MBE (80 mA/mm, 35 mS/mm) gate dielectric. (C) 2008 American Vacuum Society.