Investigations on HfO2/n-GaAs(110) interface, in-situ obtained by Oxide-MBE

Abstract

Hafnium oxide (HfO₂) thin films were deposited on n-type gallium arsenide (GaAs) substrates by Oxide-Molecular Beam Epitaxy (Oxide-MBE) method using Hafnium (Hf) metallic flow in an oxidizing atmosphere of 10^-6 mbar molecular oxygen. The Hf metallic flow was provided by an e-beam evaporator and a deposition rate of ∼ 10 nm/h was established. Semiconductor surface preparation was done prior to deposition, beginning with chemical wet etching and aggressively adjusted by in-situ treatments until a desired stoichiometry was reached. Heterojunctions with HfO₂ thin layers of 1 nm, 3 nm, 10 nm and 20 nm were fabricated. X-Ray Photoelectron Spectroscopy (XPS) and ARXPS(Angle Resolved XPS) in-situ analyses provided a clear picture of the structure of the interfaces, the chemical bonds and their composition. The interfaces are chemically stable and abrupt. A small amount of Ga₂O₃ provides a passivating effect of the semiconductor surface. The electrical properties of the heterostructures were determined using the Kraut method and Reflection Electron Energy Loss Spectroscopy (REELS) technique. Band offsets of ΔE_C=1.75 eV and ΔE_V=2.62 eV confirm a high application potential. Additionally, data on the morphology and continuity of the layers were obtained by Atomic Force Microscopy (AFM) technique while the amorphous growth was monitored by XRD(X-ray Diffraction), GIXRD (Grazing Incidence XRD) and XRR(X-ray Reflectivity) measurements. The dielectric layers showed values of the constant k in the range of 19-22, established by electrical measurements on MOS type capacitors.