Electronic structure and band parameters for ZnX (X = O, S, Se, Te)

First-principles density-functional calculations have been performed for zinc monochalcogenides with zinc-blende- and wurtzite-type structures. It is shown that the local-density approximation underestimates the band gap, misplaces the energy levels of the Zn-3d states, and overestimates the crystal-field splitting energy. Without spinorbit coupling, the order of the states at the top of VB is found to be normal for all the ZnX phases considered. Upon inclusion of the spinorbit coupling in calculations, ZnO in zinc-blende- and wurtzite-type phases become anomalous. It is shown that the Zn-3d electrons are responsible for the anomalous order. The effective masses of electrons and holes have been calculated and found that holes are much anisotropic and heavier than the electrons in agreement with experimental findings. The typical errors in calculated band gaps and related parameters originate from strong Coulomb correlations, which are found to be highly significant in ZnO. The LDA+U approach is found to correct the strong correlation of the Zn-3d electrons, and thus improves the agreement with the experimentally established location of the Zn-3d levels. Consequently, it increases significantly the parameters underestimated in the pure LDA calculations.Comment: 7 pages, 3 figures, 2 tables, ICAM-ICMAT conference, 200

Evidence for Shape Co-existence at medium spin in 76Rb

Four previously known rotational bands in 76Rb have been extended to moderate spins using the Gammasphere and Microball gamma ray and charged particle detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV. The properties of two of the negative-parity bands can only readily be interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model calculations if they have the same configuration in terms of the number of g9/2 particles, but they result from different nuclear shapes (one near-oblate and the other near-prolate). These data appear to constitute a unique example of shape co-existing structures at medium spins.Comment: Accepted for publication in Physics Letters

Deep electronic states in ion-implanted Si

In this paper we present an overview of the deep states present after ion-implantation by various species into n-type silicon, measured by Deep Level Transient Spectroscopy (DLTS) and high resolution Laplace DLTS (LDLTS). Both point and small extended defects are found, prior to any anneal, which can therefore be the precursors to more detrimental defects such as end of range loops. We show that the ion mass is linked to the concentrations of defects that are observed, and the presence of small interstitial clusters directly after ion implantation is established by comparing their behaviour with that of electrically active stacking faults. Finally, future applications of the LDLTS technique to ion-implanted regions in Si-based devices are outlined.</p

The PHENIX Experiment at RHIC

The physics emphases of the PHENIX collaboration and the design and current status of the PHENIX detector are discussed. The plan of the collaboration for making the most effective use of the available luminosity in the first years of RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program available at http://www.rhic.bnl.gov/phenix

A comparison of low-energy as ion implantation and impurity-free disordering induced defects in N-type GaAs epitaxial layers

We have compared the electrical properties of n-type GaAs layers disordered by either 40 keV As ion implantation or an impurity-free process employing an SiO2 capping layer. Current–voltage and capacitance–voltage measurements on Au Schottky barrier diodes fabricated on the processed layers showed that the impurity-free method retained the much better electrical quality of the GaAs epitaxial layers. Different sets of defects were observed in the implanted samples and impurity free disordered samples, which meant that the charge transfer across the Schottky barriers was different in the two cases. Our results further reveal that the concentrations and diffusion lengths of defects created by ion implantation were much larger. The impurity-free method retains the better electrical quality of the semiconductor material

Divacancy-oxygen and trivacancy-oxygen complexes in silicon: Local vibrational mode studies

Fourier transform infrared absorption spectroscopy was used to study the evolution of multivacancy-oxygen-related defects in the temperature range 200-300 °C in Czochralski-grown Si samples irradiated with MeV electrons or neutrons. A clear correlation between disappearance of the divacancy (V 2) related absorption band at 2767 cm-1 and appearance of two absorption bands positioned at 833.4 and 842.4 cm-1 at 20 K (at 825.7 and 839.1 cm-1 at room temperature) has been found. Both these two emerging bands have previously been assigned to a divacancy-oxygen defect formed via interaction of mobile V2 with interstitial oxygen (O i) atoms. The present study shows, however, that the two bands arise from different defects since the ratio of their intensities depends on the type of irradiation. The 842.4 cm-1 band is much more pronounced in neutron irradiated samples and we argue that it is related to a trivacancy-oxygen defect (V3O) formed via interaction of mobile V3 with Oi atoms or/and interaction of mobile V 2 with VO defects. © (2010) Trans Tech Publications

Trivacancy-oxygen complex in silicon: Local vibrational mode characterization

FTIR study of the evolution of multivacancy-oxygen-related defects in the temperature range 100-350 °C in Czochralski-grown Si samples irradiated with different particles (10 MeV electrons and 5 MeV neutrons) has been carried out. Appearance of two absorption bands positioned at 833.4 and 842.4 cm-1 has been found upon annealing of the divacancy related absorption band at 2767 cm-1. The 833.4 cm-1 band is assigned to a divacancy-oxygen defect. The 842.4 cm-1 band is much more pronounced in neutron irradiated samples and we argue that it is related to a trivacancy-oxygen defect formed via interaction of mobile V3 with Oi atoms. © 2009 Elsevier B.V. All rights reserved