Silicon Quantum Wires Oxidation and Transport Studies
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SILICON QUANTUM WIRES OXIDATION AND TRANSPORT STUDIES H.I. Liu, D.K. Biegelsen*, N.M. Johnson*, F.A. Ponce*, N.I. Maluf, R.F.W. Pease Stanford University, Solid State Laboratory, Stanford, CA. 94305 *Xerox Palo Alto Research Center, Electronic Materials Laboratory, Palo Alto, CA. 94304
ABSTRACT Fabricating well controlled nanostructures and obtaining precise structural, electrical, and optical information from them are essential for understanding the intrinsic properties of silicon (Si) nanostructures, which in turn is important for exploring the potential of quantum confinement induced light emission from crystalline Si. A combination of high resolution electron beam lithography, anisotropic reactive ion etching (RIE), and thermal oxidation has been successfully applied to obtain sub-5 nm Si columnar structures [1]. A transmission electron microscopy (TEM) technique has also been used to characterize the precise structural dimensions of these columns [1]. To obtain the electrical and optical information, a process based on polyimide planarization was developed to establish electrical contacts to these nanostructures. The same process is also applicable for fabricating device structures to study electrically pumped optical response. Preliminary transport studies have confirmed current conduction through the Si nano-pillars and yielded an estimate of the conductivity.
INTRODUCTION The intense visible room temperature luminescence from electrochemically etched porous silicon (Si) has generated much interest and a great deal of controversy regarding the underlying mechanism responsible for photon emission from a supposedly indirect material [2,3]. Various models including quantum confinement induced radiative transition have been proposed to explain this phenomenon. However, because of the inherent difficulties in assessing its structural properties and relating them to the photonic response, a self-consistent model has yet to be found. In order to study quantum confinement radiative transition in a systematic manner, a well controlled nanostructure is desirable. Toward this end, a feasible fabrication process based on high resolution electron beam lithography, anisotropic RIE, and thermal oxidation was developed to fabricate Si columnar structures with sub-5 nm diameters. Moreover, a TEM technique was also developed to obtain exact structural information from these columns. In the previous study, photoluminescence (PL) signal was also obtained from these patterned Si nanostructures [1]. However, due to the low fill factor of these lithographically defined structures, the signal was quite weak and led to some ambiguities in its origin. The small capture cross section for the incident primary photons was a great concern in the PL experiment. An electrically pumped luminescence is a more definitive experiment for confirming the origin of a photonic response. With this method, not only is the background photonic source eliminated, but the extent of excitation is also only limited by how much current one can conduct thr
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