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- 1. Appl. Phys. Lett. 90, 021920 (2007) , “Hydrogen passivation of nitrogen in GaNAs and GaNP alloys: How many H atoms are required for each N atom?”, I. A. Buyanova, W. M. Chen, M. Izadifard, S. J. Pearton, C. Bihler, M. S. Brandt, Y. G. Hong, and C. W. TuSecondary ion mass spectrometry and photoluminescence are employed to evaluate the origin and efficiency of hydrogen passivation of nitrogen in GaNAs and GaNP. The hydrogen profiles are found to closely follow the N distributions, providing unambiguous evidence for their preferential binding as the... (Read more)
- 2. Phys. Rev. B 75, 195335 (2007) , “Computational and experimental imaging of Mn defects on GaAs (110) cross-sectional surfaces”, A. Stroppa, X. Duan, M. Peressi, D. Furlanetto, and S. ModestiWe present a combined experimental and computational study of the (110) cross-sectional surface of Mn δ-doped GaAs samples. We focus our study on three different selected Mn defect configurations not previously studied in detail, namely surface interstitial Mn, isolated and in pairs, and... (Read more)
- 3. Phys. Rev. B 75, 195207 (2007) , “Effects of optical absorption on 71Ga optically polarized NMR in semi-insulating GaAs: Measurements and simulations”, Stacy Mui, Kannan Ramaswamy, and Sophia E. HayesThe intensity and the hyperfine shift of optically polarized NMR (OPNMR) signals of 71Ga in semi-insulating GaAs have been found to depend on the photon energy and the helicity of light used for optical pumping. Single-crystal GaAs wafers of two different thicknesses, 400 and 175 ... (Read more)
- 4. Phys. Rev. B 75, 115205 (2007) , “Stability of I3 complexes in III-V compound semiconductors by tight-binding molecular dynamics”, G. Zollo and F. GalaIntrinsic interstitials in GaAs are known to have a large formation energy that makes their concentration almost negligible in as-grown materials. However, interstitials must be explicitly considered in implanted GaAs where collision cascades, induced by the energetic ions, produce a large amount of... (Read more)
- 5. Phys. Rev. B 75, 113310 (2007) , “Hole spin polarization in GaAs:Mn/AlAs multiple quantum wells”, V. F. Sapega, O. Brandt, M. Ramsteiner, K. H. Ploog, I. E. Panaiotti, and N. S. AverkievWe study the effect of confinement on the spin polarization of holes bound to Mn acceptors in paramagnetic GaAs:Mn/AlAs multiple quantum wells. It is demonstrated that the polarization of these bound holes is governed by the properties of the host material rather than by quantum confinement. The... (Read more)
- 6. Phys. Rev. Lett. 98, 206403 (2007) , “H-Induced Dangling Bonds in H–Isoelectronic-Impurity Complexes Formed in GaAs1-yNy Alloys”, A. Amore Bonapasta, F. Filippone, and G. MattioliComplexes formed by H and the isoelectronic impurity N in GaAs1-yNy alloys have been widely investigated because the significant effects of N on the GaAs properties and their passivation by H represent a unique tool for a defect engineering of semiconductors.... (Read more)
- 7. Phys. Rev. Lett. 98, 077601 (2007) , “Multiple-Pulse Coherence Enhancement of Solid State Spin Qubits”, W. M. Witzel and S. Das SarmaWe describe how the spin coherence time of a localized electron spin in solids, i.e., a solid state spin qubit, can be prolonged by applying designed electron spin resonance pulse sequences. In particular, the spin echo decay due to the spectral diffusion of the electron spin resonance frequency... (Read more)
- 8. Phys. Rev. Lett. 98, 026802 (2007) , “Microscopic Basis for the Mechanism of Carrier Dynamics in an Operating p-n Junction Examined by Using Light-Modulated Scanning Tunneling Spectroscopy”, Shoji Yoshida, Yuya Kanitani, Ryuji Oshima, Yoshitaka Okada, Osamu Takeuchi, and Hidemi ShigekawaThe doping characteristics and carrier transport in a GaAs p-n junction were visualized with a ~10 nm spatial resolution, using light-modulated scanning tunneling spectroscopy. The dynamics of minority carriers under operating conditions, such as recombination, diffusion, and electric... (Read more)
- 9. Physica B 401, 250 (2007) , Elsevier , “Doubly charged state of EL2 defect in MOCVD-grown GaAs ”, Nazir A. Naz, Umar S. Qurashi, Abdul Majid and M. Zafar IqbalEL2 is the ubiquitous native defect in crystalline GaAs grown by a variety of different techniques. It has been proposed to be a doubly charged deep-level center with two states having distinct energy levels in the band gap. While the singly charged state has been the subject of many experimental studies and is, therefore, well established, the doubly charged state has only been occasionally alluded to in the literature. This paper provides evidence for a dominant inadvertent deep level in p-type GaAs most likely to be the doubly charged state of the EL2 center. Deep-level transient spectroscopy (DLTS) has been applied to characterize epitaxial layers of p-type GaAs grown on p+ GaAs substrates by low-pressure metal organic chemical vapor deposition (LP-MOCVD). A pronounced peak is observed in the majority carrier (hole) emission deep-level spectra. Thermal emission rate of holes from the corresponding deep level is found to exhibit a strong electric field dependence, showing an increase of more than two orders of magnitude with an increase of the electric field by a factor of~2. The thermal activation energy for this level is found to vary from 0.29 to 0.61 eV as the electric field is varied from 2.8×105 to 1.4×105 V/cm. Direct pulse-filling measurements point to a temperature-dependent behavior of the hole capture cross section of this level. We identify this inadvertent deep-level defect, commonly observed in p-type AsGa grown by a variety of different methods, with the doubly charged state of the well-known AsGa antisite related defect, EL2. (Read more)
- 10. Advances in Science and Technology 46, 73 (2006) , Trans Tech Publications, Switzerland , “Electric-Field-Enhanced Thermal Emission from Osmium-Related”, M. Zafar Iqbal, A. Majid, A. Dadgar and D. BimbergDeep-level defects related with 5d transition metal, osmium (Os) have been studied in ntype GaAs. Os has been incorporated in epitaxial n-GaAs layers in situ, during growth by lowpressure metal-organic chemical vapour phase epitaxy (MOVPE) technique. Mesa p+nn+ junction diodes are fabricated for investigations by deep level transient spectroscopy (DLTS). Two deeplevel peaks, observed in majority carrier (electron) emission spectra, Os1 and Os2, show a significant shift in peak positions to lower temperatures with the applied junction reverse bias, demonstrating enhancement of the thermal emission rate by the junction electric field. Doublecorrelation DLTS (DDLTS) measurements have been employed for accurate quantitative investigations of the observed field dependence. However, in view of the relatively small concentration of the deep level Os1, this technique is found to yield reliable data only for the deep level corresponding to the dominant peak, Os2. Detailed data have been obtained on the field effect for Os2, extending over junction electric field values 3 x 106 V/m - 1.2 x 107 V/m. The measured emission rate signatures show a reduction of the thermal activation energy from 0.48 eV to 0.21 eV for Os2 over this electric field range. Analysis of the data in terms of the recent theoretical work on field dependence indicates that Os2 is associated with a substitutional Os donor. (Read more)
- 11. Appl. Phys. Lett. 89, 231901 (2006) , “Cathodoluminescence investigations of GaInNAs on GaAs(111)B”, J. Miguel-Sánchez, U. Jahn, A. Guzmán, and E. MuñozIn this work, we present a detailed cathodoluminescence characterization of GaInNAs quantum wells grown on GaAs(111)B. As-grown and annealed InGaAs and GaInNAs quantum wells were maeasured and compared by spatially resolved cathodoluminescence at different photon energies. In the case of... (Read more)
- 12. Appl. Phys. Lett. 89, 152910 (2006) , “Characterization of atomic-layer-deposited Al2O3/GaAs interface improved by NH3 plasma pretreatment”, Hong-Liang Lu, Liang Sun, Shi-Jin Ding, Min Xu, David Wei Zhang, and Li-Kang WangAl2O3 thin films were deposited by atomic layer deposition on HF-cleaned and NH3 plasma-treated GaAs surfaces, respectively. The precursors used for Al2O3 films are trimethylaluminum and water. Effects of NH3 plasma pretreatment on... (Read more)
- 13. Appl. Phys. Lett. 89, 092103 (2006) , “Electron energy barriers at interfaces of GaAs(100) with LaAlO3 and Gd2O3”, V. V. Afanas'ev, A. Stesmans, R. Droopad, M.Passlack, L.F. Edge, D. G. SchlomElectron energy barriers at the interfaces of GaAs(100) with Gd2O3 appear to be insensitive to the Fermi level pinning indicating that charges at interface states are of marginal importance for the band alignment at semiconductor/insulator interfaces. The inferred conduction... (Read more)
- 14. Appl. Phys. Lett. 89, 061903 (2006) , “Nitrogen related vacancies in GaAs based quantum well superlattices”, J. Slotte, K. Saarinen, E.-M. Pavelescu, T. Hakkarainen, and M. PessaThe authors report on the influence of nitrogen incorporation on vacancies in GaAs based superlattices. The samples were molecular beam epitaxy grown on p-type GaAs substrates with the superlattice structure consisting of ten periods of quantum well material separated by GaAs buffers. Three... (Read more)
- 15. Appl. Phys. Lett. 89, 012505 (2006) , “Diffusion and clustering of substitutional Mn in (Ga,Mn)As”, Hannes Raebiger, Maria Ganchenkova, and Juhani von BoehmThe Ga vacancy mediated microstructure evolution of (Ga,Mn)As during growth and postgrowth annealing is studied using a multiscale approach. The migration barriers for the Ga vacancies and substitutional Mn together with their interactions are calculated using first principles, and temporal... (Read more)
- 16. J. Appl. Phys. 100, 083521 (2006) , “Thermally activated charge reversibility of gallium vacancies in GaAs”, Fedwa El-Mellouhi, Norm, and MousseauThe dominant charge state for the Ga vacancy in GaAs has been the subject of a long debate, with experiments suggesting −1, −2, or −3 as the best answer. We revisit this problem using ab initio calculations to compute the effects of temperature on the Gibbs free energy of... (Read more)
- 17. J. Appl. Phys. 100, 064910 (2006) , “Defects in Ga(In)NAs thin films grown by atomic H-assisted molecular beam epitaxy”, Yukiko Shimizu, Yusuke Mura, Akira Uedono, and Yoshitaka OkadaThe vacancy-type defects in Ga1yInyNxAs1x dilute nitride films grown by atomic H-assisted molecular beam epitaxy (H-MBE) were investigated. The positron annihilation measurements showed that the densities of... (Read more)
- 18. J. Appl. Phys. 100, 053516 (2006) , “Damage production in GaAs and GaAsN induced by light and heavy ions”, C. Björkas, K. Nordlund, K. Arstila, J. Keinonen, V. D. S. Dhaka, and M. PessaIon irradiation causes damage in semiconductor crystal structures and affects charge carrier dynamics. We have studied the damage production by high-energy (100 keV10 MeV) H, He, Ne, and Ni ions in GaAs and GaAs90N10 using molecular dynamics computer simulations. We... (Read more)
- 19. J. Appl. Phys. 100, 044503 (2006) , “Dislocation dynamics in strain relaxation in GaAsSb/GaAs heteroepitaxy”, B. Pérez Rodríguez and J. Mirecki MillunchickThe real-time stress evolution has been investigated during molecular-beam epitaxial growth of GaAs1xSbx/GaAs metamorphic buffer. These real-time data were obtained using an in situ multibeam optical sensor measurement and has been combined with... (Read more)
- 20. J. Appl. Phys. 100, 034503 (2006) , “Deep level defects in proton radiated GaAs grown on metamorphic SiGe/Si substrates”, M. González, C. L. Andre, R. J. Walters, S. R. Messenger, J. H. Warner, J. R. Lorentzen, A. J. Pitera, E. A. Fitzgerald, and S. A. RingelThe effect of 2 MeV proton radiation on the introduction of deep levels in GaAs grown on compositionally graded SiGe/Si substrates was investigated using deep level transient spectroscopy (DLTS). Systematic comparisons were made with identical layers grown on both GaAs and Ge substrates to directly... (Read more)
- 21. Nature 442, 436 (2006) , “Atom-by-atom substitution of Mn in GaAs and visualization of their hole-mediated interactions”, D. Kitchen, A. Richardella, J. -M. Tang, M. E. Flatt, A. YazdaniThe discovery of ferromagnetism in Mn-doped GaAs1 has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices2, 3, 4. A major hurdle for realistic applications of Ga1-XMnXAs, or other dilute magnetic semiconductors, remains that their ferromagnetic transition temperature is below room temperature. Enhancing ferromagnetism in semiconductors requires us to understand the mechanisms for interaction between magnetic dopants, such as Mn, and identify the circumstances in which ferromagnetic interactions are maximized5. Here we describe an atom-by-atom substitution technique using a scanning tunnelling microscope (STM) and apply it to perform a controlled study at the atomic scale of the interactions between isolated Mn acceptors, which are mediated by holes in GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn–Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga1-XMnXAs structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples. (Read more)
- 22. Phys. Rev. B 74, 245205 (2006) , “Mn incorporation in as-grown and annealed (Ga,Mn)As layers studied by x-ray diffraction and standing-wave fluorescence”, V. Holý, Z. Matj, O. Pacherová, V. Novák, M. Cukr, K. Olejník, and T. JungwirthA combination of high-resolution x-ray diffraction and a technique of x-ray standing-wave fluorescence at grazing incidence is employed to study the structure of a (Ga,Mn)As-diluted magnetic semiconductor and its changes during post-growth annealing steps. We find that the film is formed by a... (Read more)
- 23. Phys. Rev. B 74, 241303(R) (2006) , “Enhancement of interactions between magnetic ions in semiconductors due to declustering”, A. Franceschetti, S. V. Barabash, J. Osorio-Guillen, A. Zunger, and M. van SchilfgaardeIt is often assumed that the exchange interaction between two magnetic ions in a semiconductor host depends only on the distance and orientation of the magnetic ions. Using first-principles electronic structure calculations of Mn impurities in GaAs, we show that the exchange interaction between two... (Read more)
- 24. Phys. Rev. B 74, 235213 (2006) , “Mn 3d electronic configurations in (Ga1−xMnx)As ferromagnetic semiconductors and their influence on magnetic ordering”, F. Kronast, R. Ovsyannikov, A. Vollmer, H. A. Dürr, W. Eberhardt, P. Imperia, D. Schmitz, G. M. Schott, C. Ruester, C. Gould, G. Schmidt, K. Brunner, M. Sawicki, and L. W. MolenkampWe applied x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) at the Mn 2p-3d resonances to study the Mn 3d electronic configuration and the coupling of Mn 3d magnetic moments in various Ga1−xMnxAs films.... (Read more)
- 25. Phys. Rev. B 74, 205207 (2006) , “Charge-dependent migration pathways for the Ga vacancy in GaAs”, Fedwa El-Mellouhi, Norm, and MousseauUsing a combination of the local-basis ab initio program SIESTA and the activation-relaxation technique we study the diffusion mechanisms of the gallium vacancy in GaAs. Vacancies are found to diffuse to the second neighbor using two different mechanisms, as well as to the first and fourth... (Read more)
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