Experimental and First-Principles Theoretical Study of Structural and Electronic Properties in Tantalum-Doped In₂O₃ Semiconductor: Finding a Definitive Hyperfine Interaction Assignment

Abstract

In this work we present an experimental and theoretical study from first-principles of the structural, electronic, and hyperfine properties of Ta-doped In2O3 semiconductor. The ab initio electronic structure calculations in the Ta-diluted In2O3 system enabled to obtain the structural lattice distortions and the hyperfine parameters when the Ta atom is placed at each cationic site of the bixbyite crystal structure. To this purpose we used the full-potential augmented plane wave plus local orbital (FP-APW+lo) method, within the density functional theory. The obtained results indicate that the substitutional Ta probe-impurity produces strong changes on the local structure. In addition, we performed accurate time-differential perturbed γ–γ angular correlations (TDPAC) key experiments in 181Hf­(→181Ta)-implanted In2O3 samples with high crystallinity, in order to obtain high quality measurements of the electric-field gradient tensor (EFG) that unraveled the controversy settled in the literature and overcome dissimilar interpretations of previously reported TDPAC experiments. The experiments were performed at room temperature in air, after each step of a series of thermal annealing treatments in air at increasing temperatures in order to remove radiation damage and locate the 181Hf probes at substitutional cationic sites. We succeeded to obtained two well-defined hyperfine interactions that were assigned to 181Ta probes located at the two defect-free inequivalent cationic sites of the In2O3 crystal structure. The EFG calculations are in excellent agreement with the results of these TDPAC measurements, and show that the largest component of the diagonalized EFG, V 33, at the Ta site has mainly p character. The accuracy of the experiments together with the reliable and precise ab initio results allowed a definitive determination of the EFG at both cationic sites in this system. Formation energy calculations of defects were needed to determine the charge state of the 181Ta impurity, which agrees with a semiconducting character for the In2O3:Ta doped system.

Experimental TDPAC and Theoretical DFT Study of Structural, Electronic, and Hyperfine Properties in (111In → )111Cd-Doped SnO2 Semiconductor: Ab Initio Modeling of the Electron-Capture-Decay After-Effects Phenomenon

“…Due to this r –3 dependence, the EFG at the Cd site is basically originated in the nonspherical electronic charge density very close to the Cd nucleus (in the first bump of the Cd’s radial wave functions) . It is important to notice here that, as occurred in many other doped binary oxide systems, ,,, these approximations predict the same EFG tensor (within the precision of the calculations) when the same structural positions are employed. The V 33 direction is parallel to the [11̅0] crystal axis (see Figures and ) for all these charge states and is the same that it has in pure SnO 2 and Ta-doped SnO 2 at Sn and Ta sites, respectively .…”

“…We studied the convergence of the structural relaxations and the hyperfine parameters in other SCs formed by 2 × 2 × 2 and 2 × 2 × 4 unit cells, checking that the 2 × 2 × 3 SC was sufficient to simulate the isolated impurity, as usually occurs in oxides with an impurity−impurity shortest distance of around 10 Å. 13,15,18 In order to describe real samples, and particularly in our case where an electronic recombination process around the impurity occurs, it is essential to be able to predict with accuracy the charge state of the impurity and therefore to describe correctly the structural, electronic, and hyperfine properties of the impurity−host system. In this sense, we performed calculations for different charge states of the impurity taking into account the nominal double acceptor character of Cd 2+ when it replaces a Sn 4+ in the SnO 2 host.…”

“…In the last years, in condensed-matter physics, structural, electronic, and magnetic properties in pure and doped systems have been carefully studied at the atomic scale confronting results from hyperfine experimental techniques with reliable all-electron (AE) ab initio predictions in the framework of the density functional theory (DFT). − In particular, the subnanoscopic environment of impurities or native atoms in solids can be studied employing the time-differential perturbed γ–γ angular-correlation (TDPAC) spectroscopy. This technique provides a very precise characterization of the electric-field-gradient (EFG) tensor at diluted (ppm) radioactive probe atoms.…”

Activation and Enhancement of Room-Temperature Ferromagnetic Exchange in (Cu,N)-codoped In2O3 Dilute Magnetic Nanowires

“…To understand in detail the mechanism for the enhancement of RT ferromagnetism in the (Cu,N)-codoped In 2 O 3 nanowires, we employed the MedeA-VASP code within the framework of the density functional theory to calculate the density of states (DOS) and magnetic coupling between Cu ions for the Cu-doped and (Cu,N)-codoped In 2 O 3 . , Two of the nearest neighboring host In atoms were chosen to be substituted with two Cu atoms separated by a single O atom to build the Cu–O–Cu configuration in the In 2 O 3 supercell. The O atom between two Cu atoms was further substituted with one N atom to build the Cu–N–Cu configuration.…”

Electric field gradient study on pure and Cd-doped In(111) surfaces: Correlation between experiments at the atomic scale and first-principles calculations

“…Nowadays, confronting precise experimental determinations of the EFG tensor with very accurate theoretical predictions [9,14,[18][19][20][21][22][23][24][25][26], using all-electron state-of-the-art ab initio electronic structure calculations in the framework of the density functional theory (DFT) [27,28], it is possible to obtain valuable information about structural lattice deformations, localization and charge state of impurities and defect centers, impurity energy levels, and structural and magnetic phase transitions, among other interesting properties. The correlation between the EFG and the electronic charge density ρ( r) in a physical system is so strong that the agreement between the experimental and predicted EFG validates the ρ( r) description and hence all the ground-state properties.…”