Detail, looking up at figure of Mickiewicz; Adam Bernard Mickiewicz (1798-1855) was a Polish poet, publisher and political writer of the Romantic period. Mickiewicz was active in the struggle to achieve independence for Poland (from Russia) and so lived in exile. He settled first in Rome, later in Paris, where he became professor of Slavic literature at the Collège de France. Mickiewicz is depicted on top of the column as a pilgrim, with his left arm raised. Source: Wikipedia; http://en.wikipedia.org/wiki/Main_Page (accessed 5/7/2011

Valavanis, A

Ikonic, Z

Kelsall, RW

English

Detail, mourning figures at base (The Three Polands); Adam Bernard Mickiewicz (1798-1855) was a Polish poet, publisher and political writer of the Romantic period. Mickiewicz was active in the struggle to achieve independence for Poland (from Russia) and so lived in exile. He settled first in Rome, later in Paris, where he became professor of Slavic literature at the Collège de France. Mickiewicz is depicted on top of the column as a pilgrim, with his left arm raised. Source: Wikipedia; http://en.wikipedia.org/wiki/Main_Page (accessed 5/7/2011

Bourdelle, Emile Antoine

MIT Libraries Dome

Monument à Mickiewicz

Relief and inscription on base of column; Adam Bernard Mickiewicz (1798-1855) was a Polish poet, publisher and political writer of the Romantic period. Mickiewicz was active in the struggle to achieve independence for Poland (from Russia) and so lived in exile. He settled first in Rome, later in Paris, where he became professor of Slavic literature at the Collège de France. Mickiewicz is depicted on top of the column as a pilgrim, with his left arm raised. Source: Wikipedia; http://en.wikipedia.org/wiki/Main_Page (accessed 5/7/2011

Detail, signature of artist and date; Adam Bernard Mickiewicz (1798-1855) was a Polish poet, publisher and political writer of the Romantic period. Mickiewicz was active in the struggle to achieve independence for Poland (from Russia) and so lived in exile. He settled first in Rome, later in Paris, where he became professor of Slavic literature at the Collège de France. Mickiewicz is depicted on top of the column as a pilgrim, with his left arm raised. Source: Wikipedia; http://en.wikipedia.org/wiki/Main_Page (accessed 5/7/2011

Detail, looking up at figure of Mickiewicz and allegorical figure beneath; Adam Bernard Mickiewicz (1798-1855) was a Polish poet, publisher and political writer of the Romantic period. Mickiewicz was active in the struggle to achieve independence for Poland (from Russia) and so lived in exile. He settled first in Rome, later in Paris, where he became professor of Slavic literature at the Collège de France. Mickiewicz is depicted on top of the column as a pilgrim, with his left arm raised. Source: Wikipedia; http://en.wikipedia.org/wiki/Main_Page (accessed 5/7/2011

White Rose Research Online

promoting access to White Rose research papers    White Rose Research Online eprints@whiterose.ac.uk    Universities of Leeds, Sheffield and York http://eprints.whiterose.ac.uk/    This is an author produced version of a conference paper published in The Ninth International Conference on Intersubband Transitions in Quantum Wells.  White Rose Research Online URL for this paper:  http://eprints.whiterose.ac.uk/43346/     Paper: Valavanis, A, Ikonic, Z and Kelsall, RW n-Type Si/SiGe quantum cascade structures. In: The Ninth International Conference on Intersubband Transitions in Quantum Wells, Ambleside, UK.    n-type Si/SiGe quantum cascade structuresA. Valavanis, Z. Ikonic´ and R. W. KelsallInstitute of Microwaves and PhotonicsSchool of Electronic and Electrical EngineeringUniversity of LeedsLeeds LS2 9JTEmail: a.valavanis05@leeds.ac.ukThe quantum cascade laser (QCL) has provedextremely successful in III-V materials systems.As intersubband rather than interband optical tran-sitions are employed and the emission energiesdepend primarily on the widths of the layers,the indirect bandgap of silicon is no longer anobstacle to achieving optical emission. The use ofSi/SiGe heterostructures would enable integrationwith conventional CMOS technology and poten-tially reduce QCL fabrication costs. Whilst mostefforts to date have focussed on intersubband tran-sitions in the valence band,[1], [2] there are somedisadvantages to this approach. The large non-parabolicity of the valence band leads to linewidthbroadening, whilst the possibility of light-hole toheavy-hole optical transitions adds complexity todevices.n-type devices have six almost parabolic con-duction band ∆-minima located near the X-points,and intersubband transitions yield much lowerenergy dispersion with respect to small shiftsin wavevector. Electroluminescence linewidths aretherefore expected to be smaller than in p-typestructures. Designing devices for optical transi-tions far from the Γ-point raises several inter-esting challenges. The lattice mismatch betweenheterolayers causes a strain-induced splitting ofthe degeneracy between the ∆-valleys, resultingin two distinct sets — a ∆z set with wavevectorsperpendicular to the growth plane and a ∆xyset for the parallel case. f-type phonon scat-tering mechanisms can cause carriers to draininto orthogonal valley states and prevent opticalemission. We show however, within a one-bandeffective mass/envelope function model that it ispossible to strain the quantum wells sufficiently toseparate the two sets of states. Quantum confine-ment induced splitting of the ∆z-valley states isalso taken into consideration.[3]Electron-phonon, interface-roughness and al-loy disorder scattering mechanisms are used toinvestigate populations of states in a quantumcascade structure, whilst considering realistic Geinterdiffusion and dopant segregation. Taking allthese effects into account, a design is presentedfor population inversion and intersubband opticalemission from n-Si/SiGe heterostructures.REFERENCES[1] G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist,K. Ensslin, D. Grutzmacher, and E. Muller, “Intersubbandelectroluminescence from silicon-based quantum cascadestructures,” Science, vol. 290, pp. 2277–2280, Dec. 2000.[2] S. A. Lynch, D. J. Paul, P. Townsend, G. Matmon, Z. Suet,R. W. Kelsall, Z. Ikonic´, P. Harrison, J. Zhang, D. J.Norris, A. G. Cullis, C. R. Pidgeon, P. Murzyn, B. Murdin,M. Bain, H. S. Gamble, M. Zhao, and W.-X. Ni, “Towardsilicon-based lasers for terahertz sources,” IEEE J. Sel.Topics Quantum Electron., vol. 12, no. 6, pp. 1570–1578,2006.[3] T. B. Boykin, G. Klimeck, M. Friesen, S. N. Coppersmith,P. von Allmen, F. Oyafuso, and S. Lee, “Valley splittingin low-density quantum-confined heterostructures studiedusing tight-binding models,” Phys. Rev. B, vol. 70, Oct.2004.