The Effect of Nb Incorporation on the Electronic Properties of Anodic HfO₂

Abstract

Hafnium oxide and Nb doped HfO2 were grown by anodizing sputtering-deposited Hf and Hf-4at.%Nb. Photoelectrochemical characterization was carried out in order to estimate solid state properties such as band gap, flat band potential and electrons internal photoemission threshold energy as a function of thickness and composition of anodic oxides. Optical transitions at energy lower than the band gap value of the investigated anodic films were evidenced, and they are attributed to optical transitions involving localized states inside the band gap. Such states were located at 3.6 eV and 3.9 eV below the conduction band edge for the Nb free and Nb containing hafnium oxide, respectively. Impedance measurements were performed in a wide range of electrode potentials under anodic and cathodic polarization with respect to the flat band potential, confirming the formation of insulating oxides with high dielectric constant. The latter increases from 20 to 41 due to incorporation of Nb into the oxide

Revisiting anodic alumina templates: from fabrication to applications

“…The process of electrochemical oxidation of a metal, also known as anodization, is a simple and low-cost electrochemical process that produces an oxide layer on the target metallic surface over large areas. This process has been used to obtain nanoporous, nanotubular, or other kinds of nanostructured functional oxide layers on a wide variety of metals and semimetals, such as gold 78 , cobalt 79 , cupper 80 , gallium 81 , hafnium 82 , iron 83 , molybdenum 84 , To better understand the formation process of such nanoporous structure, one has first to understand how a simpler structure, namely non-porous anodic aluminium oxide films, are produced. In this case, solutions with pH 5-7 in which the anodic aluminum oxide is insoluble are used.…”

Electrochemical Oxidation of Hf–Nb Alloys as a Valuable Route to Prepare Mixed Oxides of Tailored Dielectric Properties

“…Moreover, as disclosed in Figure b, the highest ε ox is measured for the mixed oxide grown on Hf–39 at% Nb alloy (i.e., 45), which is roughly twice the dielectric constant of pure HfO 2 (20) and comparable to the dielectric constant of Nb 2 O 5 (40–50) …”

“…By extrapolating to zero ( I ph hν ) 2/ n versus hν , it is possible to get the value of E g opt that can be coincident to the bandgap, E g , for an ideal semiconductor/electrolyte junction, or to the mobility gap, E g m , for an amorphous semiconductor/electrolyte junction . In the case of anodic HfO 2 and Nb‐doped HfO 2 , E g opt was related to the optical transitions between the localized states, due to the presence of negatively charged oxygen vacancies, and conduction band extended states . Considering indirect optical transitions, we calculated E g opt for all the investigated mixed anodic oxides (as shown in Figure ) and the values are summarized in Table S1 (Supporting Information).…”

“…To achieve these challenging dielectric targets, high‐ k thin films must be used, such as hafnium oxide (HfO 2 ), that is a promising candidate to replace SiO 2 as gate dielectric in CMOS–based and logic devices, and as metal oxide for resistive random access memory . This interest arises because hafnium oxide combines a large bandgap ( E g = 5.1–6.1 eV), a dielectric permittivity (ε = 16–25) significantly higher than that of silicon oxide (3.9), high thermal stability, and high thermodynamic stability in contact with silicon.…”

Tuning of the Mg Alloy AZ31 Anodizing Process for Biodegradable Implants

“…From eq 2 , E d can be easily estimated. Knowing the electric field strength, it is possible to estimate the anodizing ratio, à , that is the forming factor, according to the following equation 47 The knowledge of the anodizing ratio allows us to estimate the barrier anodic layer as the product of à and the formation voltage. In the case of the anodic growth on AZ31 alloy in glycerol-based and phosphate-containing electrolyte, the voltage useful to estimate the barrier layer thickness is 120 V, that is, until the anodizing voltage increases linearly with time.…”