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- 1. J. Appl. Phys. 101, 013707 (2007) , “Vanadium donor and acceptor levels in semi-insulating 4H- and 6H-SiC”, W. C. Mitchel, W. D. Mitchell, G. Landis, H. E. Smith, Wonwoo Lee, and M. E. ZvanutThe electronic levels of vanadium in semi-insulating 4H- and 6H-SiC have been reinvestigated using temperature dependent Hall effect and resistivity measurements at temperatures up to 1000 K in conjunction with electron paramagnetic resonance (EPR) and optical absorption measurements... (Read more)
- 2. 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)
- 3. Phys. Rev. B 75, 085416 (2007) , “Ab initio theoretical study of hydrogen and its interaction with boron acceptors and nitrogen donors in single-wall silicon carbide nanotubes”, A. GaliSilicon carbide nanotubes have a great potential for biological applications. It is of interest to explore the electronic properties of these nanotubes, and how those are modified in the presence of impurities. Hydrogen is a common impurity that can appear during the growth of silicon carbide... (Read more)
- 4. Phys. Rev. B 75, 033301 (2007) , “Microscopic evidence for evolution of superconductivity by effective carrier doping in boron-doped diamond: 11B-NMR study”, H. Mukuda, T. Tsuchida, A. Harada, Y. Kitaoka, T. Takenouchi, Y. Takano, M. Nagao, I. Sakaguchi, T. Oguchi, and H. KawaradaWe have investigated the superconductivity discovered in boron-doped diamonds by means of 11B-NMR on heteroepitaxially grown (111) and (100) films. 11B-NMR spectra for all of the films are identified to arise from the substitutional B(1) site as single occupation and lower... (Read more)
- 5. Phys. Rev. Lett. 98, 135506 (2007) , “Possible Approach to Overcome the Doping Asymmetry in Wideband Gap Semiconductors”, Yanfa Yan, Jingbo Li, Su-Huai Wei, and M. M. Al-JassimThe asymmetry doping problem has severely hindered the potential applications of many wideband gap (WBG) materials. Here, we propose a possible approach to overcome this long-standing doping asymmetry problem for WBG semiconductors. Our approach is based on the reduction of the ionization energies... (Read more)
- 6. Phys. Rev. Lett. 98, 096805 (2007) , “Observation of the Linear Stark Effect in a Single Acceptor in Si”, L. E. Calvet, R. G. Wheeler, and M. A. ReedThe Stark splitting of a single fourfold degenerate impurity located within the built-in potential of a metal-semiconductor contact is investigated using low temperature transport measurements. A model is developed and used to analyze transport as a function of temperature, bias voltage, and... (Read more)
- 7. Phys. Rev. Lett. 98, 045501 (2007) , “Dopability, Intrinsic Conductivity, and Nonstoichiometry of Transparent Conducting Oxides”, Stephan Lany and Alex ZungerExisting defect models for In2O3 and ZnO are inconclusive about the origin of conductivity, nonstoichiometry, and coloration. We apply systematic corrections to first-principles calculated formation energies ΔH, and validate our theoretical defect model against... (Read more)
- 8. Phys. Rev. Lett. 98, 015501 (2007) , “First-Principles Simulations of Boron Diffusion in Graphite”, I. Suarez-Martinez, A. A. El-Barbary, G. Savini, and M. I. HeggieBoron strongly modifies electronic and diffusion properties of graphite. We report the first ab initio study of boron interaction with the point defects in graphite, which includes structures, thermodynamics, and diffusion. A number of possible diffusion mechanisms of boron in graphite are... (Read more)
- 9. Appl. Phys. Lett. 89, 182110 (2006) , “Picosecond spin relaxation of acceptor-bound exciton in wurtzite GaN”, H. Otake, T. Kuroda, T. Fujita, T. Ushiyama, A. Tackeuchi, T. Chinone, J.-H. Liang, and M. KajikawaThe spin relaxation process of acceptor-bound excitons in wurtzite GaN is observed by spin-dependent pump and probe reflectance measurement with subpicosecond time resolution. The time evolutions measured at 15–50 K have a single exponential component corresponding to the electron spin... (Read more)
- 10. Appl. Phys. Lett. 89, 112107 (2006) , “Determination of the concentration of recombination centers in thin asymmetrical p-n junctions from capacitance transient spectroscopy”, Juan A. Jiménez Tejada, Pablo Lara Bullejos, Juan A. López Villanueva, Francisco M. Gómez-Campos, Salvador Rodríguez-Bolívar, and M. Jamal DeenRecombination centers in thin asymmetrical p-n junctions were analyzed in the context of capacitance transient experiments. The combined effect of the thin low-doped region of the junction and the nonzero value of the occupation factor of the recombination center in the depletion layer... (Read more)
- 11. Appl. Phys. Lett. 89, 092122 (2006) , “Deep acceptor states in ZnO single crystals”, H. von Wenckstern, R. Pickenhain, H. Schmidt, M. Brandt, G. Biehne, M. Lorenz, M. Grundmann, and G. BrauerThe authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n-conducting ZnO... (Read more)
- 12. Appl. Phys. Lett. 89, 042106 (2006) , “Identification of acceptor states in Li-doped p-type ZnO thin films”, Y. J. Zeng, Z. Z. Ye, J. G. Lu, W. Z. Xu, L. P. Zhu, B. H. Zhao, and Sukit LimpijumnongWe investigate photoluminescence from reproducible Li-doped p-type ZnO thin films prepared by dc reactive magnetron sputtering. The LiZn acceptor state, with an energy level located at 150 meV above the valence band maximum, is identified from free-to-neutral-acceptor transitions.... (Read more)
- 13. Appl. Phys. Lett. 89, 041910 (2006) , “Acceptor segregation and nonlinear current-voltage characteristics in H2-sintered SrTiO3”, Seong-Min Wang and Suk-Joong L. KangThe current-voltage characteristics with acceptor segregation at grain boundaries have been investigated in H2-sintered SrTiO3. Al-added SrTiO3 was sintered in H2 and then annealed in air for selective oxidation of grain boundaries. The samples showed... (Read more)
- 14. Appl. Phys. Lett. 88, 152116 (2006) , “Donor and acceptor competitions in phosphorus-doped ZnO”, F. X. Xiu, Z. Yang, L. J. Mandalapu, and J. L. LiuPhosphorus-doped ZnO films were grown by molecular-beam epitaxy with a GaP effusion cell as dopant source. Three growth regions were identified to obtain ZnO films with different conduction types. In the oxygen-extremely-rich region, phosphorus-doped ZnO films show n-type conduction with... (Read more)
- 15. J. Appl. Phys. 100, 034309 (2006) , “Critical size for defects in nanostructured materials”, Jagdish NarayanThis paper addresses some of the fundamental issues and critical advantages in reducing the grain size/feature size to the nanoscale regime. We find that as the grain size or feature size is reduced, there is a critical size below which the defect content can be reduced virtually to zero. This... (Read more)
- 16. 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)
- 17. Phys. Rev. B 74, 245216 (2006) , “Influence of excited states of a deep substitutional dopant on majority-carrier concentration in semiconductors”, Hideharu MatsuuraThe density (NA) and energy level (EA) of an acceptor in a p-type wide-band-gap semiconductor (e.g., SiC, GaN, and diamond) are determined by a least-squares fit of the charge neutrality equation to the temperature dependence of the hole... (Read more)
- 18. 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)
- 19. Phys. Rev. B 74, 144432 (2006) , “Role of defects in ferromagnetism in Zn1−xCoxO: A hybrid density-functional study”, C. H. PattersonExperimental studies of Zn1−xCoxO as thin films or nanocrystals have found ferromagnetism and Curie temperatures above room temperature and that p- or n-type doping of Zn1−xCoxO can change its magnetic... (Read more)
- 20. Phys. Rev. B 74, 081201 (2006) , “Design of shallow acceptors in ZnO: First-principles band-structure calculations”, Jingbo Li, Su-Huai Wei, Shu-Shen Li, and Jian-Bai Xiap-type doping is a great challenge for the full utilization of ZnO as short-wavelength optoelectronic material. Due to a large electronegative characteristic of oxygen, the ionization energy of acceptors in ZnO is usually too high. By analyzing the defect wave-function character, we propose... (Read more)
- 21. Phys. Rev. Lett. 97, 255902 (2006) , “Atomistic Mechanism of Boron Diffusion in Silicon”, Davide De Salvador, Enrico Napolitani, Salvatore Mirabella, Gabriele Bisognin, Giuliana Impellizzeri, Alberto Carnera, and Francesco PrioloB diffuses in crystalline Si by reacting with a Si self-interstitial (I) with a frequency g and so forming a fast migrating BI complex that can migrate for an average length λ. We experimentally demonstrate that both g and λ strongly depend on the free hole... (Read more)
- 22. Phys. Rev. Lett. 97, 106802 (2006) , “Role of Pr Segregation in Acceptor-State Formation at ZnO Grain Boundaries”, Yukio Sato, James P. Buban, Teruyasu Mizoguchi, Naoya Shibata, Masatada Yodogawa, Takahisa Yamamoto, and Yuichi IkuharaThe role of Pr doping on double Schottky barrier formations at ZnO single grain boundaries was investigated by the combination of current-voltage measurements, atomic-resolution Z-contrast scanning transmission electron microscopy, and first-principles calculations. Although Pr segregated to... (Read more)
- 23. J. Appl. Phys. 95, 1884-1887 (2004) , “Thermal activation of Mg-doped GaN as monitored by electron paramagnetic resonance spectroscopy”, M. E. Zvanut, D. M. Matlock, R. L. Henry, Daniel Koleske, Alma WickendenThe microscopic process involved with thermal activation of the Mg acceptors in GaN epitaxial films is investigated using electron paramagnetic resonance (EPR) spectroscopy. Samples were heat treated in dry N2 for 30 min at temperatures between 200 and 1000 °C. Below 850 °C, the... (Read more)
- 24. Phys. Rev. B 70, 205209 (2004) , “Deep acceptor states of platinum and iridium in 4H-silicon carbide”, J. Grillenberger, U. Grossner, B. G. Svensson, F. Albrecht, W. Witthuhn, R. SielemannBand gap states of platinum and iridium in the hexagonal polytype 4H of silicon carbide are investigated by means of deep level transient spectroscopy (DLTS) in n- as well as p-type epitaxial layers. To establish a definite chemical assignment of band gap states to Pt and Ir the... (Read more)
- 25. Phys. Rev. B 70, 115203 (2004) , “Different roles of carbon and silicon interstitials in the interstitial-mediated boron diffusion in SiC”, Michel Bockstedte, Alexander Mattausch, and Oleg PankratovThe interstitial and vacancy mediated boron diffusion in silicon carbide is investigated with an ab initio method. The boron interstitials in p-type and n-type materials are found to be far more mobile than the boron-vacancy complexes. A kick-out mechanism and an interstitialcy... (Read more)
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