Character of states near the Fermi level in (Ga,Mn)As: Impurity to valence band crossover

T. Jungwirth, Jairo Sinova, A. H. MacDonald, B. L. Gallagher, V. Novák, K. W. Edmonds, A. W. Rushforth, R. P. Campion, C. T. Foxon, L. Eaves, E. Olejník, J. Mašek, S.-R. Eric Yang, J. Wunderlich, C. Gould, L. W. Molenkamp, T. Dietl, and H. Ohno
Phys. Rev. B 76, 125206 – Published 18 September 2007

Abstract

We discuss the character of states near the Fermi level in Mn-doped GaAs, as revealed by a survey of dc transport and optical studies over a wide range of Mn concentrations. A thermally activated valence-band contribution to dc transport, a midinfrared peak at energy ω200meV in the ac conductivity, and the hot photoluminescence spectra indicate the presence of an impurity band in low-doped (1% Mn) insulating GaAs:Mn materials. Consistent with the implications of this picture, both the impurity-band ionization energy inferred from the dc transport and the position of the midinfrared peak move to lower energies, and the peak broadens with increasing Mn concentration. In metallic materials with >2% doping, no traces of Mn-related activated contribution can be identified in dc transport, suggesting that the impurity band has merged with the valence band. No discrepancies with this perception are found when analyzing optical measurements in the high-doped GaAs:Mn. A higher-energy (ω250meV) midinfrared feature which appears in the metallic samples is associated with inter-valence-band transitions. Its redshift with increased doping can be interpreted as a consequence of increased screening, which narrows the localized-state valence-band tails and weakens higher-energy transition amplitudes. Our examination of the dc and ac transport characteristics of GaAs:Mn is accompanied by comparisons with its shallow acceptor counterparts, confirming the disordered valence-band picture of high-doped metallic GaAs:Mn material.

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  • Received 9 July 2007

DOI:https://doi.org/10.1103/PhysRevB.76.125206

©2007 American Physical Society

Authors & Affiliations

T. Jungwirth1,2, Jairo Sinova3, A. H. MacDonald4, B. L. Gallagher2, V. Novák1, K. W. Edmonds2, A. W. Rushforth2, R. P. Campion2, C. T. Foxon2, L. Eaves2, E. Olejník1, J. Mašek5, S.-R. Eric Yang6, J. Wunderlich7, C. Gould8, L. W. Molenkamp8, T. Dietl9,10, and H. Ohno11,12

  • 1Institute of Physics, ASCR v.v.i., Cukrovarnická 10, 162 53 Praha 6, Czech Republic
  • 2School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
  • 3Department of Physics, Texas A&M University, College Station, Texas 77843-4242, USA
  • 4Department of Physics, University of Texas at Austin, Austin, Texas 78712-1081, USA
  • 5Institute of Physics, ASCR v.v.i., Na Slovance 2, 182 21 Praha 8, Czech Republic
  • 6Department of Physics, Korea University, Seoul 136-701, Korea
  • 7Hitachi Cambridge Laboratory, Cambridge CB3 0HE, United Kingdom
  • 8Physikalisches Institut (EP 3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
  • 9Institute of Physics, Polish Academy of Science, Aleja Lotnikow 32/46, PL 02-668 Warszawa, Poland
  • 10Institute of Theoretical Physics, Warsaw University, PL 00-681 Warszawa, Poland
  • 11Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
  • 12ERATO Semiconductor Spintronics Project, Japan Science and Technology Agency, Kitamemachi 1-18, Aoba-ku, Sendai 980-0023, Japan

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Vol. 76, Iss. 12 — 15 September 2007

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