Spectroscopic identification of the chemical interplay between defects and dopants in Al-doped ZnO

Abstract

The conduction and optoelectronic properties of transparent conductive oxides can be largely modified by intentional inclusion of dopants over a very large range of concentrations. However, the simultaneous presence of structural defects results in an unpredictable complexity that prevents a clear identification of chemical and structural properties of the final samples. By exploiting the unique chemical sensitivity of Hard X-ray Photoelectron Spectra and Near Edge X-ray Absorption Fine Structure in combination with Density Functional Theory, we determine the contribution to the spectroscopic response of defects in Al-doped ZnO films. Satellite peaks in O1s and modifications at the O K-edge allow the determination of the presence of H embedded in ZnO and the very low concentration of Zn vacancies and O interstitials in undoped ZnO. Contributions coming from substitutional and (above the solubility limit) interstitial Al atoms have been clearly identified and have been related to changes in the oxide stoichiometry and increased oxygen coordination, together with small lattice distortions. In this way defects and doping in oxide films can be controlled, in order to tune their properties and improve their performances.

ZnO Thin Films Growth Optimization for Piezoelectric Application

“…The same compression was assigned in previous works to the presence of defects in the oxide [50,51]. We previously demonstrated that our ZnO films grown at RT in Ar are over-stoichiometric in oxygen, due to the presence of Zn vacancies and O interstitials [29]. Further indications of the crystalline quality of the film are the 2θ (0002) and the rocking curve (RcC) full width at half maximum (FWHM) across the Bragg diffraction peak.…”

“…The same compression was assigned in previous works to the presence of defects in the oxide [ 50 , 51 ]. We previously demonstrated that our ZnO films grown at RT in Ar are over-stoichiometric in oxygen, due to the presence of Zn vacancies and O interstitials [ 29 ].…”

“…Among them, PVD, and in particular magnetron sputter deposition, allow us to maintain a good control on the film growth conditions to obtain reproducible and controllable properties in c-axis-oriented ZnO films of tens to hundreds nm thickness [3]. As an example, sputter deposition allows obtaining good insulating films with controlled defects [28,29]. However, for sputter-deposited ZnO films, the typical d33 values reported in the literature are of few pm/V [30,31], lower than those obtained in films grown with other techniques.…”

Transparent conductive oxide-based architectures for the electrical modulation of the optical response: A spectroscopic ellipsometry study

“…0 4  % was chosen because it has already been reported that it is the optimum doping level for highly conductive and transparent AZO films 18 . Increasing doping above this value induces the appearance of states in the gap near the valence band maximum, which are related to the defects introduced in the oxide, that reduce the number of free carriers and probably also their mobility 20 .…”

Demonstration of Near Edge X-ray Absorption Fine Structure Spectroscopy of Transition Metals Using Xe/He Double Stream Gas Puff Target Soft X-ray Source

“…Among these heavier elements, there are several transition metals of particular interest to researchers, i.e., Fe, Co, Ni, Cu, Zn, as well as their oxides [ 14 , 15 ] and compounds [ 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. These interests are related to their magnetic [ 23 , 24 ], optical [ 25 ], as well as conductive and semi-conductive [ 20 , 21 , 26 ] properties, which in turn translate to possible applications in catalytic, photocatalytic and photoelectrocatalytic (PEC) processes [ 14 , 27 , 28 , 29 ], as electrodes in photovoltaic cells and lithium-ion batteries [ 30 , 31 , 32 ], optoelectronic and plasmonic devices [ 15 , 25 , 33 ], gas sensors [ 34 ] or drug delivery [ 16 , 35 ].…”