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Suche nach „[Stirner] [Thomas]“ hat 139 Publikationen gefunden
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    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    S. Jackson, P. Harrison, W. Hagston, S. Bardorf, Thomas Stirner, J. Nicholls

    Zeeman studies of CdTe-Cd1-xMnxTe multiquantum wells

    Posterpräsentation

    6th International Conference on Modulated Semiconductor Structures, Garmisch-Partenkirchen

    1993

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    P. Harrison, W. Hagston, Thomas Stirner, J. Nicholls

    Excitonic relaxation channels in double quantum wells

    8th International Conference on Hot Carriers in Semiconductors, Oxford, Großbritannien

    1993

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

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

    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

    P. Harrison, W. Hagston, Thomas Stirner, M. O’Neill

    Exciton dynamics in multiquantum well CdTe-Cd1-xMnxTe systems

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

    1993

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

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

    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. Jackson, P. Harrison, W. Hagston, B. Lunn, Thomas Stirner, J. Nicholls, J.H.C. Hogg, D. Ashenford

    Molecular-beam epitaxy investigation of interface disorder effects in magnetic II-VI quantum wells

    Journal of Vacuum Science & Technology B, vol. 11, no. 3, pp. 881-884

    1993

    Abstract anzeigen

    The present article describes the results of a combined theoretical and experimental investigation into the quality of the interfaces of II–VI quantum well structures grown by molecular‐beam epitaxy (MBE). Detailed information is presented on the dilute magnetic semiconductor system CdTe/Cd1-xMnxTe in which the CdTe forms the well and the Cd1-xMnxTe forms the barrier. Structures are grown routinely in which both the photoluminescence (PL) and photoluminescence excitation (PLE) linewidths are narrow (∼1–2 meV). This is indicative of high quality material, a feature which is confirmed by the x‐ray data in which Pendellösung fringes can be seen. However, in spite of this, it is found that although the same growth conditions are nominally employed quantum well structures are obtained which show either (i) different discernible structures in the PL and the PLE spectra, or (ii) marked differences in the Stokes’ shift between the PLE and PL from one sample to the next. A related feature concerns observations of an asymmetrical magnetic field splitting of the heavy‐hole exciton states in the barriers. The results of theoretical calculations of the exciton energy levels and their associated linewidths are presented. A comparison of theory with the experimental observations shows that the above effects can be accounted for in terms of interface disorder and magnetic field dependent interface potentials. Thus in case (i) above, the relative intensity of the components in the PLE is different from that in the PL. This is consistent with large island growth in the plane of the well, large here meaning that the island diameters exceed those of the exciton diameter (∼140–150 Å). Observations of a Stokes’ shift, even though the absorption and emission lines are narrow, can be accounted for theoretically if the concept of smaller scale disorder is i- - ntroduced, i.e., island sizes that are small compared with the diameter of the exciton. Finally, results are presented which show a remarkable asymmetry in the Zeeman splitting of the heavy‐hole exciton lines. It is shown that this can be accounted for by introducing deep, short‐range interface potentials (∼1 or 2 monolayers). The latter are magnetic field dependent, the source of the asymmetry being attributed to band‐gap renormalization effects. The implications of all these results for MBE growth conditions are described.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

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

    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, Thomas Stirner, J. Nicholls, D. Ashenford

    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.

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    Zeitschriftenartikel

    P. Harrison, W. Hagston, Thomas Stirner, R. Roberts

    Stark ladders in strongly coupled finite superlattices

    Journal de Physique IV, vol. 3, no. C5, pp. 203-206

    1993

    Abstract anzeigen

    It is shown that the nature and extent of wavefunction localisation of miniband states in an external electric field can be markedly different for finite superlattice structures, compared with infinite and is dependent on the strength of interaction between the initial electron (and hole) miniband states. The question of blue shifts and excitonic effects is described and possible device applications for strongly interacting superlattices structures are discussed.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

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

    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.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    P. Harrison, W. Hagston, Thomas Stirner

    Violation of the Delta n=0 selection rule for optical transitions in magnetic sawtooth quantum wells

    Solid State Communications, vol. 86, no. 12, pp. 815-818

    1993

    Abstract anzeigen

    Sawtooth quantum wells, in which the graded gap is produced by a linear variation in the concentration of a magnetic ion, offer a unique opportunity to investigate the additional optical transitions resulting from symmetry breaking. In the present theoretical work linear variations in the concentration of the magnetic Mn2+ ion in the Cd1−xMnxTe alloy permits a study of the variation of both the energy and oscillator strength of forbidden transitions as a function of the external magnetic field. The resulting variations in the symmetry of the system produces profound effects on the oscillator strengths of the Δn≠0 transitions.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    P. Harrison, W. Hagston, J. Goodwin, Thomas Stirner

    Band gap renormalization and observation of the type I-type II transition in quantum well systems

    Journal of Applied Physics, vol. 73, no. 10, pp. 5081-5087

    1993

    Abstract anzeigen

    Quantum wells (or barriers) are of finite extent (≤100 Å) along the growth direction. Hence, for at least one or two monolayers adjacent to the interface, the corresponding one‐electron potential in the conduction (or valence) band must differ from that appropriate to the bulk material. The present article demonstrates the pronounced effect such short‐range ‘‘interface potentials’’ can have on the transition energies and oscillator strengths in a dilute magnetic semiconductor system undergoing a type I–type II transition in an external magnetic field.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

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

    Interface disorder and the inhomogeneous broadening of optical spectra in semiconductor quantum wells

    Superlattices and Microstructures, vol. 13, no. 4, pp. 431-435

    1993

    Abstract anzeigen

    The photoluminescence linewidth of a CdTe/Cd1-xMnxTe structure, grown by molecular beam epitaxy, containing quantum wells of width 26, 37 and 45Å separated by large (250Å) barriers, was investigated. The high quality of the quantum well structure was confirmed by X-ray topography, X-ray rocking curves and narrow photoluminescence lines. It is shown that these results are consistent with small scale interface roughness resulting from clusters involving pairs or triplets of Mn2+ ions forming into small islands.

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    Zeitschriftenartikel

    P. Harrison, W. Hagston, Thomas Stirner

    Excitons in diffused quantum wells

    Physical Review B - condensed matter and materials physics, vol. 47, pp. 16404-16409

    1993

    Abstract anzeigen

    The Schrödinger equation corresponding to the potential profile resulting from manganese diffusion in CdTe-Cd1-xMnxTe quantum wells has been solved using a numerical method. Calculation of the exciton binding energies has allowed predictions of the effect of diffusion on the resulting optical properties of such quantum-well structures. In addition to the magnetic-field-dependent potential profiles that accompany the diffusion process, it is shown that the ratio of the Zeeman splitting of the light- and heavy-hole excitonic transitions is strongly dependent on the extent of the manganese diffusion. Consequently, this ratio can be used as a measure of the diffusion coefficient.

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    Vortrag

    P. Harrison, W. Hagston, Thomas Stirner

    Origin of the Stokes’ shift in semiconductor quantum wells

    Posterpräsentation

    European Workshop on II-VI Semiconductors, Aachen

    1992

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    P. Harrison, W. Hagston, J. Goodwin, Thomas Stirner

    Dynamical aspects of free exciton magnetic polaron formation in CdTe-Cd1-xMnxTe quantum wells

    Posterpräsentation

    European Workshop on II-VI Semiconductors, Aachen

    1992

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    S. Jackson, P. Harrison, W. Hagston, B. Lunn, Thomas Stirner, J. Nicholls, J.H.C. Hogg, D. Ashenford

    Molecular-beam epitaxy investigation of interface disorder effects in magnetic II-VI quantum wells

    Posterpräsentation

    12th North American Conference on Molecular Beam Epitaxy, Ottawa, Kanada

    1992

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Vortrag

    P. Harrison, W. Hagston, J. Goodwin, Thomas Stirner

    Effect of interface disorder on Stokes’ shift and photoluminescence line width in CdTe-CdMnTe microstructures

    IoP Meeting on Strained Layer Structures & Devices, Sheffield, Großbritannien

    1992

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Beitrag (Sammelband oder Tagungsband)

    Thomas Stirner

    Origin of the Stokes’ shift in semiconductor quantum wells (lecture)

    Universität Würzburg/Fakultät für Physik und Astronomie

    Jahrbücher für Nationalökonomie und Statistik, vol. 209

    1992