Anion Antisite Defects Research Articles

Effect of Mg deficiency on the thermoelectric properties of Mg2(Si, Sn) solid solutions

In this study, we analyze the change in the thermoelectric properties of a Mgx(Si, Sn) system upon varying nominal Mg content x (x = 1.8, 1.9, 2.1, 2.2, 2.3). We find that Mg deficiency induces multiple point defects, such as Mg vacancies and anion anti-site defects, as well as phase separation of crystal structure, both of which alter the band structure. Systematic investigations are followed to elucidate how thermoelectric properties of a Mgx(Si, Sn) system are influeced by the degree of Mg deficiency. Temperature-dependent measurements of the Seebeck coefficient and the Hall coefficient indicate that Mg deficiency induces p-type behavior; this is confirmed by an analysis of the thermoelectric transport properties by using a single parabolic band model at low temperature. The p-type conduction in the Mg-deficient system suggests that Mg vacancies are the predominant defects. However, the efficiency of p-type doping is two to three orders of magnitude lower (∼1018 cm−3) than expected when considering only Mg vacancies as the origin of charge carriers. Density functional theory calculations suggest that the anion anti-site defect on the Mg site is attributable for the low measured carrier concentration and low doping efficiency. Moreover, the energy band structure of the Mg-deficient Mgx(Si, Sn) system is shown to undergo significant deformation and allow the formation of an impurity band at the X point due to the Mg-deficient conditions, enabling the system to have a relatively anion-rich condition. Furthermore, Mg deficiency minimizes the thermal conductivity to 1–1.5 W/m∙K at room temperature owing to an early bipolar contribution and separated structural phases. This study provides the Mg deficiency as a new control parameter that can be utilized to enhance the p-type thermoelectric performance of Mg silicides.

Defect energy levels and persistent luminescence in Cu-doped ZnS

Zinc sulfide (ZnS) based materials are widely used in many applications. Yet, due to a lack of detailed knowledge of defect energy levels, the electrical properties and luminescence mechanisms in the materials still give rise to debate. Here, we report a first-principles study of native point defects and impurities in zincblende ZnS using hybrid density-functional calculations. We find that cation and anion vacancies and antisite defects introduce deep defect levels in the band gap and can act as donors or acceptors depending on the position of the Fermi level. The substitutional impurity CuZn acts as a deep acceptor and thus does not contribute to p-type conductivity. Substitutional impurities AlZn and ClS, on the other hand, are shallow donors. More importantly, we identify the isolated (i.e., unassociated) CuZn as a source of the green luminescence observed in ZnS-based phosphors and CuZn–AlZn and CuZn–ClS defect complexes as sources of blue luminescence. The materials may have both green and blue emissions with the relative intensity dependent on the ratio between the unassociated defect and defect complex concentrations, which is also consistent with experimental observations.

Density functional theory study of the point defect energetics in γ-LiAlO2, Li2ZrO3 and Li2TiO3 materials

The defect energetics in γ-LiAlO2, Li2TiO3, and Li2ZrO3 materials used in tritium-producing burnable absorber rods and fusion solid breeder applications was investigated using density functional theory calculations. A comprehensive analysis of the charged defects was performed for cation and anion vacancies, interstitials, antisite defects, and 3H interstitial and substitutional defects to understand the defect structures at different charge states and their stability as a function of the electron chemical potential across the electronic band gap of crystals at operating temperature and oxygen partial pressure conditions. Through investigation of the local bonding configurations and projected electronic density of states of the 3H related charged defects, including 3H interstitial (3Hint), 3Hint bound with an oxygen interstitial, and substitutional 3H defects on the Li, O, and M (M = Al, Ti, and Zr) sites (3HLi, 3HO, and 3HM), the 3H states of these defects were distinguished, i.e. triton (3H+), neutral 3H (3H0), and tritide (3H−). The two stable 3H related defects under the Li2O-LiOH rich condition at T = 1000 K, between P(O2) = 10−5 and 10−25 atm were found to be 3H interstitial (3Hint) with charge of +1 and neutral 3HLi (substitutional 3H on the Li site) in γ-LiAlO2, Li2ZrO3, and Li2TiO3 materials. For Li2TiO3, the stability of the 3HO with charge of +1 and 3HM with charge of −3 becomes comparable to that of 3Hint atm at P(O2) = 10−25 atm. Overall, our results indicate the energy cost to form the stable 3H defect species (3Hint with charge of +1 and neutral 3HLi) in γ-LiAlO2 material are higher than those of Li2TiO3 and Li2ZrO3 materials at T = 1000 K, between P(O2) = 10−5 and 10−25 atm. Interactions between the point defects and the 3H species as a function of the electron chemical potential across the band gap of the materials were also examined. All the three materials exhibit strong interactions between the 3Hint and the O vacancy, Li vacancy, and O interstitial defects with the strongest interactions found in the case of γ-LiAlO2 phase, indicating a higher tendency to trap 3H at such point defects in γ-LiAlO2.

Thermal stabilities, electronic structures and optical properties of intrinsic defects and dopant cerium in Ca4F2Si2O7

The thermal stabilities, electronic structures and optical properties of intrinsic defects and dopant Ce3+ in Ca4F2Si2O7 host are studied by using density functional theory (DFT) calculations (with PBE and hybrid PBE0 functionals) and wave function-based embedded cluster ab-initio calculations (at the CASSCF/CASPT2/RASSI−SO level). The calculated formation energies reveal that anion vacancies (VO and VF) are always much more energetically favorable than cation vacancies (VCa and VSi) in Ca4F2Si2O7 host, which is generally prepared under reducing atmospheres. According to the thermodynamic transition energy levels of intrinsic defects readily generated in undoped Ca4F2Si2O7 (e.g. anion vacancies and antisite defects), we may identify the defect-induced host absorption and emission, whose exact origins are unclear previously. Moreover, on the basis of ab-initio calculated energies and relative oscillator strengths of the 4f→5d transitions of Ce3+ at calcium sites with charge-compensating defect OF in their local environments, the excitation bands in the experimental spectra of Ce3+-doped Ca4F2Si2O7 phosphors are also assigned. The main purpose of this work is to understand luminescence mechanisms of intrinsic defects and extrinsic dopants in the hosts for phosphors by using first-principles approaches.

Correlation between energy positions of deep intrinsic point-defect levels and a limiting fermi level in irradiated III–V semiconductors

The energy levels of neutral anion (VA) and cation (VC) vacancies and antisite defects are calculated for the anion CA and cation AC sublattices of III–V semiconductors. An averaged energy level position for these defects is estimated to be Eav abs = 4.9 eV. The position coincides with the local charge electroneutrality level. It is shown that the case, where the total energies of formation of VA, VC and antisite CA, AC defects in the sublattices of binary semiconductors are similar, corresponds to the point-defect equilibrium condition and stabilization of the Fermi level in the proximity of the local charge electroneutrality level.

Identification of surface anion antisite defects in (110) surfaces of III–V semiconductors

We identify surface anion antisite defects in (110) surfaces of GaAs, GaP, and InP using scanning tunneling microscopy combined with density-functional theory calculations. In contrast to subsurface arsenic antisite defects, surface antisite defects are electrically inactive and have a very localized defect state which gives rise to a distinct feature in scanning tunneling microscopy images.

Thermal equilibrium concentrations of point defects in gallium arsenide

Expressions of the thermal equilibrium concentrations of point defects in GaAs, including the neutral and charged species, are derived. These expressions are explicit functions of well-defined thermodynamic quantities, which in turn yield explicit expressions for the reaction constant K in the usual As 4 pressure power law representation of the point defect thermal equilibrium concentrations. Such power laws have been of little quantitative value in the past, because values for K were not known. In the present derivation, emphases are placed upon the difference between the Gibbs free energies of an As atom in the interior of a GaAs crystal and in an As vapor phase molecule, and the role of the crystal Fermi level. Numerical values of the thermal equilibrium concentrations of the neutral and three negatively charged Ga vacancies (V 0 Ga, V − Ga, V 2− Ga and V 3− Ga), the neutral As vacancies V 0 As and the two neutral antisite de Ga 0 As and As 0 Ga have been obtained. The calculated thermal equilibrium concentration of the anion antisite defect As 0 Ga reaches a peak value of about 1 sx 10 17 cm −3 and is practically temperature independent, in agreement with experimental findings. The thermal equilibrium concentrations of the triply negatively charged Ga vacancy V 3− Ga, C eq v 3− Ga ( n), have been found to exhibit a temperature independence or a negati temperature dependence behavior under strong n-doping conditions. That is, the C eq v 3− Ga ( n) value is either unchanged or increases as the temperature is lowered. This C eq v 3− Ga ( n) property provided explanations to a number of outstanding experimental results, either requiring the interpretation that V 3− Ga has attained its thermal equilibrium concentration at the onset of each experiment, or requiring mechanisms involving point defect nonequilibrium phenomena. The calculated C eq v 3− Ga ( n) values are in agreement with available experimental results.

Formation energies and abundances of intrinsic point defects at the GaAs/AlAs(100) interface

Formation energies and electronic structures of all intrinsic point defects on quasi-T d sites at the GaAs/AlAs(100) interface were calculated as a function of the chemical potentials of the electrons and atoms using density-functional theory. The results show that Al Ga and Ga Al with always be present in significant concentrations. Furthermore, we find that under As-rich conditions the cation vacancies and the anion antisite defects can occur in significant concentrations, whereas under As-poor conditions the cation antisites, cation interstitials and anion vacancies will play an important role.

Generation of Anion-Antisite Defects in n-Type, p-Type and Semi-Insulating InP Studied by MCD-ODMR and MCD-ODENDOR

Generation of Anion-Antisite Defects in n-Type, p-Type and Semi-Insulating InP Studied by MCD-ODMR and MCD-ODENDOR

Point defect thermal equilibria in GaAs

The thermal equilibrium concentrations of the six electrically neutral single point defect species in GaAs are expressed as explicit functions of well-defined thermodynamic quantities. The difference between the Gibbs free energies of an arsenic atom in the interior of a GaAs crystal and in an arsenic vapor phase molecule is emphasized. Numerical values of the thermal equilibrium concentrations of the gallium and arsenic vacancies and the two antisite defects are estimated. It is of interest that the calculated thermal equilibrium concentration of the anion antisite defect AsGa0 reaches a peak value of about 1 × 1017 cm−3 and is almost temperature independent. This computed value for AsGa0 is consistent with experimental findings.

EL2 and anion antisite defects in plastically deformed GaAs

We report on optical absorption its magnetic circular dichroism (MCD), optically detected electron spin-resonance (ODESR), and electron nuclear double-resonance (ODENDOR) investigations of plastically deformed semi-insulating GaAs. By plastic deformation arsenic antisite defects are created which show a similar ODESR pattern as EL2 defects present in the material prior to deformation. EL2 and the new antisite defects can be distinguished by their different spectral dependence of the MCD. The new antisite defect formation starts at 2% deformation and is investigated as a function of the degree of deformation; additional EL2 defects are not created. With ODENDOR it is shown that the atomistic structure of the EL2 defects changes in the deformed GaAs.

Anion-Antisite defects in GaAs: As and Sb

We present results of selfconsistent, first-principles calculations of total energies for AsGa and SbGa in GaAs. We confirm that both impurities in the substitutional Td site behave as double donors, and the first internal excitation appears at around 1 eV. For the neutral systems we obtain a metastable minimum in the total energy surface in a configuration with the impurity atom displaced toward the interstitial site; the transformation to this metastable configuration, however, is not expected to be operative for the SbGa defect.

Persistent photoquenching and anion antisite defects in neutron-irradiated GaAs

A potential origin for the reported discrepancies on the low-temperature photosensitivity of particle-induced anion antisites in GaAs is revealed by a systematic study of the relative fraction of photoquenchable paramagnetic As4+Ga centers as a function of neutron fluence and annealing temperature. The electron paramagnetic resonance data show that the As4+Ga centers can be split into two subsets.

Characterization of an Anion Antisite Defect as a Deep Double Donor in InP

Characterization of an Anion Antisite Defect as a Deep Double Donor in InP

Fast neutron-induced defects in undoped and iron-doped indium phosphide

Undoped and iron-doped InP samples have been investigated by conventional electron paramagnetic resonance measurements before and after fast neutron irradiations. Besides the expected anion antisite PIn defect, they reveal the presence of a broad spectrum that could be ascribed to an anion vacancy Vp on the basis of detailed linewidth and g-shift scalings of the resonance parameters of already identified intrinsic defects in GaP and InP. The irradiated InP:Fe sample shows both the nearest and next-nearest FeIn-Ini pairs.

Prediction of equilibrium defect concentrations in GaAs and ZnSe

We use the local density approximation within a self-consistent pseudopotential and pseudoatomic-orbital scheme to predict equilibrium point defect concentrations in semiconductors and their dependence on stoichiometry, temperature and Fermi level. We compare and contrast the native defects expected in GaAs (III–V) with those in ZnSe (II–VI). We find in stoichiometric p-type material that the dominant defect in GaAs is the cation on anion antisite defect, whereas the interstitial cation defect is dominant in ZnSe. The prominence of interstitials in p-type ZnSe tends to self-compensate the material since Zn I is a double donor. We also demonstrate how extrinsic impurities may affect native defect concentrations by considering as an example the Zn impurity in GaAs.

Arsenic antisite defect AsGa and EL2 in GaAs.

The microscopic structure of the paramagnetic anion antisite defect in semi-insulating GaAs was determined by optically detected electron-nuclear double resonance (ODENDOR). It is an arsenic-antisite--arsenic-interstitial (${\mathrm{As}}_{\mathrm{Ga}}$-${\mathrm{As}}_{\mathrm{i}}$) pair. It is shown, by optically detected ESR and ODENDOR experiments, that its energy levels and optical properties in the diamagnetic state are those of the EL2 defect.

Effects of alloy disorder on Schottky-barrier heights.

The effects of alloy disorder on the Schottky barriers at semiconductor-alloy--metal interfaces are investigated within the defect model of Schottky-barrier formation. The deep levels and the associated wave functions for surface antisite defects, which are believed to be responsible for the barriers considered here, were previously calculated for various III-V semiconductor alloys using the theory of deep levels and treating the alloy host in the virtual-crystal approximation. In the present paper, perturbation theory is used to treat the effect of the random local environment of each defect on these deep levels. For the cation and anion antisite defects at the (110) surfaces of six different III-V semiconductor alloys, the inhomogeneous broadening of the associated deep levels is found to range from nearly 0 to about 0.3 eV, depending on the alloy composition and the material considered. The corresponding effect on the Schottky-barrier heights which result from Fermi-level pinning by these deep levels should be a slight bowing with composition. Typically, this bowing effect is estimated to be of the order of 0.1 eV at intermediate alloy compositions.

Self‐Consistent Tight‐Binding Investigation of Chemical Trends for Native Defects in III–V Semiconductors

AbstractUsing the recently developed charge self‐consistent version of the empirical tight‐binding method (ETBM) in conjunction with the Koster‐Slater scattering‐theoretic approach the electronic properties induced by the substitutional native point defects (anion and cation antisite defect, anion and cation vacancy) in the six III–V semiconductors GaP, GaAs, GaSb, InP, InAs, and InSb are investigated. The calculations include the neutral and possible charged states of the defects. Chemical trends in the energetic position of gap states, the orbital composition, and the localization of the defect wave function are discussed and compared with other theoretical and experimental findings.

ChemInform Abstract: Microscopic Identification of Anion Antisite Defects in Gallium Arsenide by Optically Detected Magnetic Resonance

Chemischer InformationsdienstVolume 17, Issue 15 Reviews ChemInform Abstract: Microscopic Identification of Anion Antisite Defects in Gallium Arsenide by Optically Detected Magnetic Resonance J. M. SPAETH, J. M. SPAETHSearch for more papers by this authorD. M. HOFMANN, D. M. HOFMANNSearch for more papers by this authorB. K. MEYER, B. K. MEYERSearch for more papers by this author J. M. SPAETH, J. M. SPAETHSearch for more papers by this authorD. M. HOFMANN, D. M. HOFMANNSearch for more papers by this authorB. K. MEYER, B. K. MEYERSearch for more papers by this author First published: April 15, 1986 https://doi.org/10.1002/chin.198615399Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue15April 15, 1986 RelatedInformation