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Suche nach „[S.] [Weston]“ hat 9 Publikationen gefunden
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    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Thomas Stirner, W. Hagston, J. Nicholls, M. O’Neill, S. Weston, J. Miao

    Mn ion clustering in II-VI semimagnetic semiconductor heterostructures

    Physical Review B - condensed matter and materials physics, vol. 58, pp. 7040-7045

    1998

    DOI: 10.1103/PhysRevB.58.7040

    Abstract anzeigen

    The results of photoluminescence excitation experiments in Cd1-xMnxTe and Zn1-xMnxSe diluted magnetic semiconductor quantum-well structures are shown to be consistent with the occurrence of a clustering of the magnetic Mn ions. Possible clustering mechanisms are discussed briefly together with alternative explanations of the data.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Thomas Stirner, S. Weston, P. Harrison, S. Bardorf, S. Jackson, W. Hagston, J.H.C. Hogg, J. Nicholls, M. O’Neill

    Experimental determination of the effect of alloy composition on the band alignment of the CdTe-Cd1-xMnxTe heterojunction

    Physical Review B - condensed matter and materials physics, vol. 51, no. 8, pp. 5477-5479

    1995

    Abstract anzeigen

    A technique based on photoluminescence excitation measurements is described for the direct determination of the band alignment in a quantum well formed from nonmagnetic and semimagnetic materials. Results are presented for a series of CdTe-Cd1-xMnxTe quantum well samples. These show that the valence band offset, when expressed as a fraction of the total band discontinuity, is a function of the alloy concentration x in the barrier.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    W. Hagston, S. Weston, M. O’Neill, J.H.C. Hogg, D. Ashenford, B. Lunn, Thomas Stirner, P. Harrison

    Characteristic Zeeman patterns in novel graded gap II-VI quantum well structures

    Journal of Vacuum Science & Technology B, vol. 12, pp. 1146-1149

    1994

    DOI: 10.1116/1.587069

    Abstract anzeigen

    Novel methods of growing graded gap structures are described. In order to provide a check that the structures are indeed graded in the correct manner, magnetic ions in the structure have been employed. The good agreement between the predicted and observed Zeeman splitting of the corresponding light‐ and heavy‐hole exciton transitions, together with the magnetic field dependence of the Zeeman splittings and intensity of a forbidden heavy‐hole exciton transition, is taken as direct evidence that graded gap structures having the correct composition have indeed been fabricated.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    S. Weston, P. Harrison, W. Hagston, J. Nicholls, D. Ashenford, Thomas Stirner

    Optical properties of single magnetic quantum wells in an external magnetic field

    3rd International Conference on Optics of Excitons in Confined Systems, Montpellier, Frankreich

    1993

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    W. Hagston, Thomas Stirner, S. Weston, M. O’Neill, J.H.C. Hogg, B. Lunn, D. Ashenford, P. Harrison

    Characteristic Zeeman patterns in novel graded gap II-VI quantum well structures

    13th North American Conference on Molecular Beam Epitaxy, Stanford, CA, USA

    1993

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    S. Weston, M. O’Neill, J. Nicholls, J.H.C. Hogg, B. Lunn, D. Ashenford, K. Hieke, P. Harrison, W. Hagston, Thomas Stirner

    Comparative studies of excitons in magnetic asymmetric double quantum well structures

    Posterpräsentation

    3rd International Conference on Optics of Excitons in Confined Systems, Montpellier, Frankreich

    1993

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    S. Weston, J. Nicholls, M. O’Neill, P. Harrison, W. Hagston, J.H.C. Hogg, B. Lunn, D. Ashenford, Thomas Stirner

    Comparative studies of excitons in magnetic asymmetric double quantum well structures

    Journal de Physique IV, vol. 3, no. C5, pp. 401-404

    1993

    DOI: 10.1051/jp4:1993585

    Abstract anzeigen

    Four different asymmetric double quantum well structures in the dilute magnetic semiconductor system Cd1-xMnx Te have been investigated. Theoretical calculations are presented which show that the observed photoluminescence (PL) and photoluminescence excitation (PLE) energies are consistent with an anticrossing of the lowest two hole states in one of the double quantum well structures when subjected to an external magnetic field.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    S. Weston, P. Harrison, W. Hagston, J. Nicholls, D. Ashenford, Thomas Stirner

    Optical properties of single magnetic quantum wells in an external magnetic field

    Journal de Physique IV, vol. 3, no. C5, pp. 397-400

    1993

    DOI: 10.1051/jp4:1993584

    Abstract anzeigen

    Photoluminescence measurement performed on magnetic Cd1-xMnxTe quantum wells surrounded by Cd1-yMny Te barriers ([MATH]), grown by M. B. E. and subjected to an external magnetic field, are described. The observed excitation spectra are shown to be in agreement with calculations of exciton energies based on the envelope function approximation. Characteristic features of the samples are either the large ([MATH]18meV) Stokes' shift and/or the width of the P. L. lines ([MATH]11meV). These are to be contrasted with the values in comparable non-magnetic wells of CdTe where the Stokes' shift is typically less than 1 meV and the halfwidth of the P. L. lines is less than 1 or 2 meV. Arguments are presented which show that these observations, together with their magnetic field dependence, are consistent with the formation of magnetic polarons. The photoluminescence emission also contains a band attributed to excitons bound to donors. It is observed experimentally that this donor-bound exciton emission disappears with increasing magnetic field. A theoretical interpretation of the observed properties of this band is given in terms of excitons bound to donors which are situated at different positions in the well and barrier region.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    P. Harrison, W. Hagston, J. Nicholls, M. O’Neill, T. Piorek, Thomas Stirner, S. Weston

    Investigation of the effect of quantum well width on the binding energy of excitons to neutral donors

    Superlattices and Microstructures, vol. 14, no. 4, pp. 249-252

    1993

    DOI: 10.1006/spmi.1993.1133

    Abstract anzeigen

    Observations of bound exciton states in some bulk semiconductor materials has shown the validity of Haynes' rule, namely that the binding energy of the exciton to a donor is a multiple 1/ξ (say) of the binding energy of the electron to the donor (i.e., the neutral donor binding energy E D ), although in other bulk materials more general linear dependencies are required. Quantum well structures (QWS) typically exhibit such donor hound exciton complexes. There are several points of difference however, E D is a function of donor position, the donor distribution is unknown and interface roughness could also influence the donor bound exciton emission. Hence in order to determine whether a generalised form of Haynes' rule can be applied to excitons bound to donors in quantum wells of varying width requires a careful combination of theory with experiment. The binding energies of the donors at various positions in each well region must be calculated with due allowance made for the effects of interface roughness. A presumed distribution of the donor concentration is then made and, on the assumed validity of Haynes' rule, the lineshape of the bound exciton emission calculated. Comparison with the observed emission spectra will then give insight into whether Haynes' rule is satisfied as a function of position and well width in QWS. This analysis has been carried out for a series of single quantum wells, all of different widths and all grown in the same sample by the technique of molecular beam epitaxy. A careful analysis of all the data showed that Haynes' rule is not applicable--i.e., the observed exciton energies are not a constant multiple of the donor binding energy for QWS of different well width. PACS: 71.55.Gs; 78.66.Hf.