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Doping Issues in Wide Band-Gap Semiconductors

Exeter, United Kingdom
21-23 March 2001
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Talk abstract

Shallow versus deep hydrogen states in ZnO and HgO

S. F. J. Cox

ISIS Facility, Rutherford Appleton Laboratory, Chilton OX11 0QX, UK

E. A. Davis (2), S. P. Cottrell (1), P. J. C. King (1), J. S. Lord (1), J. M. Gil (4), H. V. Alberto (4), R. C. Vilao (4), J. Piroto Duarte (4), N. Ayres de Campos (4), A. Weidinger (5), R. L. Lichti (6), and S. J. C. Irvine (7)

(1) ISIS Facility, Rutherford Appleton Laboratory, Chilton OX11 0QX, UK, (2) Department of Physics and Astronomy, University College, London, London WCE 6BT, UK, (3) Department of Physics and Astronomy, University of Leicester, Leicester LEI 7RH, UK, (4) Physics Department, University of Coimbra, P--3004--516 Coimbra, Portugal, (5) Hahn-Meitner Institut Berlin, Glienicker Strasse 100, D-14109 Berlin, Germany, (6) Physics Department, Texas Tech University, Lubbock, TX 79409-1051, USA, (7) Chemistry Department, University of Wales, Bangor, Gwynedd LL57 2UW, UK

The muonium states mimicking interstitial hydrogen in ZnO and HgO are compared. Whereas in ZnO the predicted shallow donor state [1] is confirmed [2], in HgO we find a considerably deeper state, more akin to Mu* and the AA9 centre in Si. The respective ionization temperatures are around 40K and 150K and the donor ionization energies are 32+/-3 and 155+/-2 meV, deduced from the temperature dependence of the muSR signal amplitudes. (On the assumption of thermodynamic equilibrium, the donor-level depths would be twice these values.) The muSR spectra provide a comprehensive characterization of the undissociated paramagnetic states. The hyperfine parameters, which measure the electron spin density on and near the muon, differ by a factor of ~50, defining a hydrogenic radius of 1.1 nm in ZnO and indicating a much more localized state in HgO. Both show a degree of anisotropy in the hyperfine tensor which could provide further clues to site and local electronic structure. These data should largely carry over to hydrogen and provide stringent tests of further calculations. We speculate on the causes of the switch from shallow to deep behaviour, and on the competition and coexistence of shallow and deep muonium states in other wide-gap II-VI compounds.

[1] C.G. Van de Walle, Phys. Rev. Lett. 85 (2000) 1012, [2] S.F.J. Cox, E.A. Davis et al, Phys. Rev. Lett. (2001, in press).