Periodic Two-dimensional Arrays of Silicon Quantum Dots for Nanoscale Device Applications
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Periodic Two-dimensional Arrays of Silicon Quantum Dots for Nanoscale Device Applications Christopher C. Striemer, Rishikesh Krishnan, Qianghua Xie1, Leonid Tsybeskov2, and Philippe M. Fauchet Department of Electrical and Computer Engineering, University of Rochester Rochester, NY 14627, U.S.A. 1 Process and Material Characterization Laboratory, Semiconductor Product Sector, 2200 West Broadway, Mesa, AZ, 85202, U.S.A. 2 Department of Electrical and Computer Engineering, New Jersey Institute of Technology Newark, NJ 07102, U.S.A. ABSTRACT We report a successful unification of standard lithographic approaches (top down), anisotropic etching of atomically smooth surfaces, and controlled crystallization of silicon quantum dots (bottom up) to produce silicon nanoclusters at desired locations. These results complement our previous demonstration of silicon nanocrystal uniformity in size, shape, and crystalline orientation in nanocrystalline silicon (nc-Si)/SiO2 superlattices, and could lead to practical applications of silicon nanocrystals in electronic devices. The goal of this study was to induce silicon nanocrystal nucleation at specific lateral sites in a continuous amorphous silicon (a-Si) film. Nearly all previous studies of silicon nanocrystals are based on films containing isolated nanocrystals with random lateral position and spacing. The ability to define precise twodimensional arrays of quantum dots would allow each quantum dot to be contacted using standard photolithographic techniques, leading to practical device applications like high-density memories. In this work, a template substrate consisting of an array of pyramid-shaped holes in a (100) silicon wafer was formed using standard microfabrication techniques. The geometry of this substrate then influenced the crystallization of an a-Si/SiO2 superlattice that was deposited on it, resulting in preferential nucleation of silicon nanoclusters near the bottom of the pyramid holes. These clusters are clearly visible in transmission electron microscopy (TEM) images, while no clusters have been observed on the planar surface areas of the template. Possible explanations for this selective nucleation and future device structures will be discussed. INTRODUCTION In order to make a commercially viable electronic technology based on self-organized nanocrystals, the position of each nanocrystal must be controlled over a large area. Nanocrystal arrays with random positions are interesting demonstrations of crystallization techniques, but are impossible to individually contact with current device technology. Lateral ordering of III-V nanocrystals by the self organization of strained layers in non-lattice-matched material systems has been demonstrated, but is not compatible with the commercial ultra-large-scale integration (ULSI) infrastructure, and has poor long range order [1]. Chemical methods of arranging nanoparticles within two-dimensional polymer matrices have also been shown [2,3], however, the long range order and stability of these structures is not yet of
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