A hybrid functional calculation of Tm3+ defects in germanium (Ge)

Please read abstract in the article.National Research foundation (NRF) of South Africa (Grantspecific unique reference number (UID) 78838).http://www.elsevier.com/locate/mssp2017-03-31hb201

Ab initio study of aluminium impurity and interstitial-substitutional complexes in Ge using a hybrid functional (HSE)

The results of an ab initio modelling of aluminium substitutional impurity (AlGe), aluminium interstitial in Ge [IAl for the tetrahedral (T) and hexagonal (H) configurations] and aluminium interstitial-substitutional pairs in Ge (IAlAlGe) are presented. For all calculations, the hybrid functional of Heyd, Scuseria, and Ernzerhof in the framework of density functional theory was used. Defects formation energies, charge state transition levels and minimum energy configurations of the AlGe, IAl and IAlAlGe were obtained for 2, 1, 0, þ1 and þ2 charge states. The calculated formation energy shows that for the neutral charge state, the IAl is energetically more favourable in the T than the H configuration. The IAlAlGe forms with formation energies of 2.37 eV and 2.32 eV, when the interstitial atom is at the T and H sites, respectively. The IAlAlGe is energetically more favourable when the interstitial atom is at the T site with a binding energy of 0.8 eV. The IAl in the T configuration, induced a deep donor (þ2/þ1) level at EV þ 0:23 eV and the AlGe induced a single acceptor level (0/1) at EV þ 0:14 eV in the band gap of Ge. The IAlAlGe induced double-donor levels are at EV þ 0:06 and EV þ 0:12 eV, when the interstitial atom is at the T and H sites, respectively. The IAl and IAlAlGe exhibit properties of charge state-controlled metastability.This work is based on the research supported partly by the National Research foundation (NRF) of South Africa [Grant-specific Unique Reference Number (UID) 98961].http://link.springer.com/journal/116642018-07-30hb2016Physic

Rare earth interstitials in Ge : a hybrid density functional theory study

In this work, the results of density functional theory calculations for rare earth (Ce, Pr, Eu, and Er) interstitials in Ge are presented. We employed the hybrid functional of Heyd, Scuseria, and Ernzerhof (HSE06) for all the calculations. We calculated the formation energies and charge state transition levels for the tetrahedral (T) and hexagonal (H) configurations of the Ce, Pr, Eu, and Er interstitials in Ge. While for the T configuration, the charge states of the Ce and Pr did not induce any thermodynamic accessible transition state level within the band gap of Ge, for both the T and H configurations the Eu and Er interstitials in Ge induce deep levels in the band gap. The H configuration of the Ce interstitial in Ge induces a shallow donor level at 0.03 eV below the conduction band. The Eu interstitial exhibits negative-U properties for the (+2/2) transition level and the Er interstitial displays characteristics of charge state controlled metastability.Supported partly by National Research Foundation (NRF) of South Africa (Grant speci c unique reference number (UID) 98961).http://link.springer.com/journal/116642018-02-28hb2017Physic

Electronic properties of vacancies in bilayer graphane

Please read abstract in the article.The University of Pretoria and the National Institute for Theoretical Physics (NiThep).http://www.elsevier.com/locate/physbhj2019Physic

Ab-initio study of MgSe self-interstitial (Mgi and Sei)

We present detailed calculations of formation and thermodynamics transition state energies of Mgi and Sei interstitial defects in MgSe using generalized gradient approximation (GGA) and local density approximation (LDA) functional in the frame work of density functional theory (DFT). For both LDA and GGA the formation energies of Mgi and Sei are relatively low in all the configurations. The most stable Se interstitial was the tetrahedral (T) configuration having lower formation energy than the decagonal (D) configuration. The Mgi and Sei defect introduced transition state levels that had either donor or acceptor levels within the band gap. Sei acts as a donor or an acceptor and creates levels that were either deep or shallow depending on the configuration. Sei exhibit negative-U properties and show charge states metastability in the D configuration. Mgi acts as only shallow donor (+2/ + 1) in both T and D configurations, in addition we pointed out the role of Mgi as electrically activating donor.The National Research foundation (NRF) of South Africa (Grant specific unique reference number (UID) 78838).https://www.scientific.net/SSPhb2017Physic

Ab-initio study of germanium di-interstitial using a hybrid functional (HSE)

In this work, we present ab-initio calculation results of Ge di-interstitials (I2(Ge)) in the framework of the density functional theory (DFT) using the Heyd, Scuseria, and Ernzerhof (HSE) hybrid functional. The formation energy, transition levels and minimum energy con gurations were obtained for I2(Ge) -2, -1, 0, +1 and +2 charge states. The calculated formation energies shows that for all charge states of I2(Ge), the double tetrahedral (T) con guration formed the most stable defect with a binding energy of 1.24 eV in the neutral state. We found the (+2/+1) charge state transition level for the T lying below the conduction band minimum and (+2/+1) for the split[110]-tetrahedral con guration lying deep at 0.41 eV above the valence band maximum. The di -interstitials in Ge exhibited the properties of both shallow and deep donor levels at (+2/+1) within the band gap and depending on the con gurations. I2(Ge) gave rise to negative-U, with e ective-U values of -0.61 and -1.6 eV in di erent con gurations. We have compared our results with calculations of di -interstitials in silicon and available experimental data.National Research foundation (NRF) of South Africa (Grant specific unique reference number (UID) 78838).http://www.elsevier.com/locate/physb2017-01-31hb201

A first principle hybrid functional calculation of TmGe 3+-VGe defect complexes in germanium

By means of density functional theory (DFT), using the screened Heyd, Scuseria, and Ernzerhof (HSE06) hybrid functional we present results of the Tm3+Ge-VGe defect complexes in germanium (Ge). The formation energies of the rst (fnn), second (snn), third (tnn) and fourth (ftnn) nearest neighbour con gurations of Tm3+Ge-VGe were examined. The charge state transition levels for all these con gurations were examined as well. The Tm3+Ge-VGe complexes were found to have a positive binding energies for the neutral charge state in the fnn and ftnn con gurations. The thermodynamic transition levels revealed that the Tm3+Ge-VGe induced shallow levels in the band gap for the fnn, tnn and ftnn con gurations and deep level for the tnn con guration.The snn con guration showed no charge state transition level, the -2 charge state was stable for all Fermi energies in the band gap . The Tm3+Ge-VGe displayed evidence of a single donor level (+1=0) and an acceptor level (-1=-2) within the band gap. Charge state controlled metastability was exhibited by the Tm3+Ge-VGe.The National Research foundation (NRF) of South Africa (Grant specific unique reference number (UID) 78838).http://www.journals.elsevier.com/computational-condensed-matter/hb2016Physic

Rare earth interstitial-complexes in Ge : hybrid density functional studies

Please read abstract in the article.The National Research Foundation (NRF) of South Africa [98961]http://www.elsevier.com/locate/nimb2018-10-15hj2017Physic

Rare earth substitutional impurities in germanium : a hybrid density functional theory study

Please read abstract in the article.The National Research Foundation (NRF) of South Africa [(UID) 98961]http://www.elsevier.com/locate/nimb2018-10-15hj2017Physic

Induced defect levels of P and Al vacancy-complexes in 4H-SiC : a hybrid functional study

Please read abstract in the article.The National Research foundation (NRF) of South Africa (Grant specific unique reference number (UID) 98961).http://www.elsevier.com/locate/mssp2020-01-01hj2018Physic