Oxygen diffusion coefficients in the metastable ferroelectric phase of polycrystalline hafnium zirconium oxide (HZO) thin films have been quantified using 18O tracers and time-of-flight secondary ion mass spectrometry. 11.5 nm thick HZO films containing 16O were deposited by plasma-enhanced atomic layer deposition followed by post-metallization annealing to crystallize into the ferroelectric phase. A 1.2 nm thick HZO layer containing 18O was then deposited using thermal atomic layer deposition with H218O as a reactant. Thermal anneals were conducted at 300, 350, and 400 °C and the ferroelectric phase confirmed after the anneals by x-ray diffraction, infrared spectroscopy, and electrical property measurements. 18O depth profiles were measured and fit with a thin film diffusion equation to determine the oxygen diffusion coefficients. Oxygen diffusion coefficients ranged from approximately 2 × 10−18 cm2/s at 300 °C to 5 × 10−17 cm2/s at 400 °C with an activation energy of 1.02 ± 0.24 eV.

Hafnium oxide-based thin films, in particular hafnium zirconium oxide (HZO), have potential for applications in nonvolatile memory and energy harvesting. Atomic layer deposition (ALD) is the most widely used method for HZO deposition due to its precise thickness control and ability to provide conformal coverage. Previous studies have shown the effects of different metal precursors, oxidizer precursors, and process temperatures on the ferroelectric properties of HZO. However, no mechanism has been identified to describe the different phase stabilities as the metal precursor purge time varies. This study investigates how varying the metal precursor purge time during plasma-enhanced ALD (PE-ALD) influences the phases and properties of the HZO thin films. Grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy, and scanning transmission electron microscopy are used to study the changes in phase of HZO with variation of the metal precursor purge time during the PE-ALD process. The phases observed are correlated with polarization and relative permittivity responses under an electric field, including wake-up and endurance effects. The resulting phases and properties are linked to changes in composition, as measured using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. It is shown that short metal precursor purge times result in increased carbon and nitrogen impurities and stabilization of the antipolar Pbca phase. Long purge times lead to films comprising predominantly the ferroelectric Pca2 ₁ phase.

A challenge facing specific classes of wide bandgap semiconductor devices is the development of a robust dielectric insulating layer that is chemically and thermally compatible with the semiconductor. Requirements for gate dielectrics include sufficient band offsets, low leakage currents, and low interface state densities. Magnesium oxide holds promise for integration with gallium nitride (GaN), as it has been shown to meet many of these requirements in epitaxial films synthesized by molecular-beam epitaxy (MBE), pulsed laser deposition (PLD), and atomic layer deposition (ALD). Large area growth with low impurity content and smooth growth surfaces are the remaining obstacles. This study presents the results of the epitaxial growth of magnesium oxide by radio frequency (RF) magnetron sputtering on n-type GaN. An epitaxial intermixing layer between the GaN top layer and the oxide was found. Electrical characterization shows explicit depletion and accumulation of charge in metal–oxide–semiconductor devices up to 500 °C. The density of interface states at room temperature was determined using photo-assisted capacitance–voltage measurements to be as low as $2.9\times 10^{{11}}$ cm $^{-{2}}$ eV $^{-{1}}$ , showing that the interfacial phase is not detrimental to the interfacial electronic properties of the metal–oxide–semiconductor capacitor (MOSCap) devices.

Hafnia‐based ferroelectrics hold promise to reduce energy demand for computing by enabling compute‐in‐memory and as non‐volatile memories. The ferroelectric phase in this material system is, in part, stabilized by oxygen vacancies. While oxygen vacancies may be a necessity for phase stability, they limit device endurance through diffusion and accumulation into conducting channels. Herein, it is shown that oxygen diffusion is spatially variable within individual grains of ferroelectric hafnium zirconium oxide (HZO). Using ¹⁸ O tracers and finite difference modeling, it is shown that grain boundaries and regions near electrode interfaces allow for relatively rapid oxygen diffusion, with values as much as 10 ⁴ larger than the grain cores. Further, the selection of electrode material affects the diffusion coefficients across all microstructural regions. HZO films in contact with TiN electrodes result in more oxygen‐deficient HZO films and higher oxygen diffusion coefficients. Tungsten electrodes result in fewer vacancies and lower diffusion coefficients. Diffusion activation energy differences between the HZO with the two electrodes is reconciled by differing populations of charged and uncharged oxygen vacancies. This insight into the local vacancy populations and diffusion pathways provides a platform for designing hafnia‐based films, deposition processes, and integration strategies to reduce vacancy gradients and improve performance.

The temperature dependence of epitaxial growth of MgO on n-type (0001)-oriented GaN by radio frequency magnetron sputtering is investigated. Epitaxial growth is obtained for growth temperatures of 550 °C and above, but polycrystalline films are observed for 500 °C and below. For all process temperatures, it is demonstrated that an interfacial phase is present that ranges from 2 to 3 nm in thickness and does not increase in thickness with temperature. The presence of the interfacial phase is shown to originate from ion bombardment during the initial growth. The electronic properties of metal–oxide–semiconductor capacitor devices are measured. Wider hysteresis is seen in capacitance–voltage measurements for devices fabricated at lower deposition temperatures. The less stable electrical performance of films grown at lower temperatures is shown to be related to both interface and bulk defects.