Photoluminescence within Crystalline-Si/SiO 2 Single Quantum Wells.
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Photoluminescence within Crystalline-Si/SiO2 Single Quantum Wells. D. J. Lockwood1, M. W. C. Dharma-wardana1, Z. H. Lu2, D. H. Grozea2, P. Carrier3 and Laurent J. Lewis3 1 Institute for Microstructural Sciences, National Research Council, Ottawa, K1A 0R6 Canada 2 Department of Materials Science and Engineering, University of Toronto, Toronto, M5S 3E4, Canada 3 Département de Physique et Groupe de Recherche en Physique et Technologie des Couches Minces (GCM), Université de Montréal, Case Postale 6128, Succursale Centre-Ville, Montréal, Québec, H3C 3J7 Canada ABSTRACT Ultrathin single quantum wells of crystalline silicon (c-Si) confined by SiO2 have been prepared by chemical and thermal processing of silicon-on-insulator wafers. The photoluminescence (PL) produced by these nanometer-thick single wells contains two bands: one exhibits a peak energy of ~1.8 eV, while the second increases rapidly in peak energy with decreasing c-Si layer thickness. Comparison with theories based on self-consistent firstprinciples calculations shows that the increase in PL peak energy of the second band is consistent with that predicted for the c-Si energy gap of such wells. It also agrees with the measured band gap variation. The ~1.8 eV PL band is attributed to the recombination of electron-hole pairs confined at the c-Si/SiO2 interface. INTRODUCTION The discovery by Lu, Lockwood, and Baribeau [1] of intense luminescence in Si/SiO2 superlattices (SL) has led to numerous experimental [2-6] and theoretical studies [7-11] of their structural, electronic and optical properties. A blue shift with increased confinement is reported in most experimental and in all theoretical works. In general, the atomic structure of Si in the quantum well (QW) is amorphous, as for the two SiO2 barriers. This is due to the growth process in combination with the considerable lattice mismatch between silicon and silicon dioxide in their crystalline phases, being 5.43Å for diamond-like Si versus for instance 7.16Å for the beta-cristobalite SiO2. Several attempts have been conducted in order to fabricate crystalline silicon quantum wells. Takahashi et al [5] followed by Kanemitsu and Okamoto [6] have first reported the fabrication of single quantum wells obtained after adjoining two semiconductor-on-insulator (SOI) wafers. The asymmetry in the lineshape of the photoluminescence (PL) suggested the presence of two main peaks: one major PL peak (centered around 1.65 eV) that remains unshifted in all the QW samples while a minor peak undergos a blue shift with increased confinement. Thus, two main mechanisms describe the PL intensities, one unshifted energy peak that is attributed to the interfaces owing to its observation in all QWs while the other shifted energy peaks are attributed to the varying well thickness, i.e., to the confinement. We report here new results that confirm the presence of these two peaks, one major peak centered about 1.8 eV and another that increases in energy with increased confinement. These results are compared to calculations perfo
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