Abstract
Looking beyond the 16 nm node ICs, researchers have come up a consensus that high-κ dielectrics will become the channel material in the long-standing SiO2/Si system. The combination of high-κ dielectrics with channel made of III-Vs will have to be integrated onto Si. Themes of this thesis work focus on utilizing unique MBE technique to grow high quality oxides to search potential solutions to solve this issue. Two major achievements has been obtained by employing the MBE method: (I) further reducing the EOT by (a) interfacial engineering and (b) phase transition engineering, (II) the integration of GaN onto Si through the high quality MBE-grown crystalline oxide.(III) (a) By employing the MBE technique, the formation of the oxide/Si interfacial layer has been effectively suppressed. HfO2 films with 4.9 nm thickness show low leakage current density ~0.4 A/cm2 at 1V, a dielectric constant □ of 20.7, and an EOT of 0.9 nm. The composite film of ALD-HfO2(1.4 nm)/MBE-HfO2(1.5 nm) exhibits an overall□□ value of 16.2, and an EOT of 0.7 nm with a leakage current density of 5.3×10-1 A/cm2 at Vfb -1V. The Dit value at midgap is 3.6×1011 cm-2eV-1 calculated by the conductance method.(b) Cubic phase yttrium-doped HfO2 (YDH) ultrathin films were grown on both Si (111) and GaAs(100) substrates by molecular beam epitaxy. Thorough structural and morphological investigations by x-ray scattering and transmission electron microscopy reveal that the YDH thin films are epitaxially grown on the Si(111) and GaAs(100) substrates. From the electrical measurements, optimized doping concentration of yttrium into HfO2 increases the dielectric value to 32, achieving lower EOT on both Si and GaAs.(IV) The epitaxial growth of GaN on Si (111) substrates with a thin crystalline oxide (Sc2O3, or □-Al2O3) as a template/buffer layer is fabricated. The structural properties and in-situ epitaxial growth were studied using reflection high energy electron diffraction (RHEED), high-resolution transmission electron microscopy, and high-resolution x-ray diffraction. The crystalline oxide template serves as an effective barrier layer, and no cracking is observed in GaN.