Quantum Confinement in Nanocrystalline Si Superlattices
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QUANTUM CONFINEMENT IN NANOCRYSTALLINE Si SUPERLATTICES G. F. Grom*, P. M. Fauchet**, and L. Tsybeskov** Materials Science Program, Department of Mechanical Engineering "Department of Electrical and Computer Engineering University of Rochester, Rochester, NY 14627 J. P. McCaffrey, H. J. Labb6, and D. J. Lockwood, Institute for Microstructural Sciences, National Research Council, Ottawa KlA OR6, Canada ABSTRACT Photoconductance spectroscopy was used to probe the effects of quantum confinement in nanocrystalline (nc)-Si/amorphous (a)-SiO 2 superlattices (SLs). A Metal-Oxide-Semiconductor (MOS)-like structure with the nc-Si SL incorporated in the oxide was fabricated to study charging/discharging processes in Si nanocrystals. The fine structure observed in photoconductance spectra at low temperatures was interpreted in terms of singularities in the carrier density of states, possibly due to energy quantization. In addition, a low-resistance sample exhibited photocurrent oscillations with a frequency of several kHz, which could be a manifestation of sequential resonant carrier tunneling in the nc-Si/a-Si0 2 SL. INTRODUCTION Low-dimensional Si structures capped by Si0 2 are the most, promising candidates for nanoelectronics owing to the low defect density and large carrier confining potential at the Si/Si0 2 interface.' Several methods have been developed to fabricate three dimensionally (3D) confined Si nanostructures. 2 However, despite huge efforts, a precise control over the size, shape, density and electrical isolation of Si quantum dots is still lacking. Recently, we have developed a technique for growing Si nanocrystals in the form of nanocrystalline Si (nc)Si/amorphous (a)-Si0 2 superlattices (SLs). 3 The technique is based on controlled crystallization of thin a-Si layers sandwiched between a-Si0 2 layers. The major advantages of this novel structure are: (i) the size of Si nanocrystals can be controlled simply by varying the thickness of the initially deposited a-Si layer; (ii) the fabrication is based on a standard microelectronic processing and, therefore, is highly reliable. Using several characterization techniques (e.g., electrical characterization, FTIR, and low-angle X-ray reflectivity) we have shown that this structure has a very low defect density (
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