Carrier Confinement Effects in Epitaxial Silicon Quantum Wells Prepared by MOCVD
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H. Paul Maruska,*' R. Sudharsanan,* Eric Bretschneider,**, Albert Davydov,** J.E. Yu,** Balu Pathangey,** K.S. Jones*** and Timothy J. Anderson** *Spire Corporation, One Patriots Park, Bedford, MA 01730 "**Chemical Engineering Department, University of Florida, Gainesville, FL 32611 ***Materials Science Department, University of Florida, Gainesville, FL 32611 *I-Present address: N.Z. Applied Technology, 150-C New Boston Rd., Woburn, MA 01801
ABSTRACT Silicon multiquantum wells ranging in width from 3 to 15 nm were deposited on closely lattice-matched ZnS barriers. MOCVD was used to deposit the ZnS films using diethyl zinc and hydrogen sulfide as the precursors; disilane was used to deposit silicon layers at low temperatures. Single and multiple silicon nano-layers were observed by transmission electron microscopy and secondary ion mass spectrometry. Photoluminesence studies revealed emissions peaks which were blue-shifted with respect to the edge emission from bulk silicon substrates. The observation of emission from silicon nanostructures shifted to wavelengths as short as the 800-850 nm range is consistent with the effects of quantum confinement in silicon nanostructures. INTRODUCTION The present work stems from reports of bright visible light emission from "porous silicon".' The surfaces of etched porous silicon samples are covered with a myriad of microscopic silicon wires, with dimensions on the order of 1-5 nm.2 Bright photoluminescence has been observed from these silicon structures in the visible portion of the spectrum, 3 suggesting that the radiative recombination mechanism for nano-dimensional silicon is much different than the one found for the indirect band gap in bulk crystalline silicon. The ultra-small sizes of the silicon "wires" may serve to quantum confine the electrons and holes, and this strong quantum confinement may enhance scattering or phonon-related processes that make efficient radiative recombination possible, with radiative lifetimes that are very close to those encountered in direct band gap semiconductors.4 Porous silicon nanostructures are usually created by electrochemical etching.3 Material prepared by this technique has yielded bright red, yellow, and even green photoluminescence, and light-emitting diodes have been prepared by forming heterojunctions between indium tin oxide and porous silicon.' Unfortunately, the etched material tends to be structurally inhomogeneous; high magnification scanning electron photomicrographs of porous silicon reveal a dendritic structure.6 In order to investigate the properties of quantum confined silicon and, potentially, to produce a more controlled (planar) device structure, a study was initiated to grow silicon quantum wells (QW) using chemical vapor deposition. 987
Mat. Res. Soc. Symp. Proc. Vol. 358 01995 Materials Research Society
QUANTUM WELL STRUCTURE AND MATERIALS PREPARATION The structure chosen for the study consists of silicon QWs confined by lattice-matched zinc sulfide cladding layers. There is a very close lattice match between S
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