Mizuta, Hiroshi

Oda, S.

Tanaka, A.

Tsuchiya, Yoshishige

Usami, K.

Yamahata, G.

English

Southampton (e-Prints Soton)

FORMATION OF NANOCRYSTALLINE SILICON QUANTUM DOT ARRAYS Atsushi Tanaka, Gento Yamahata, Yoshishige Tsuchiya, Hiroshi Mizuta and Shunri Oda Quantum Nanoelectronics Research Center and Department of Physical Electronics, Tokyo Institute of Technology and SORST-JST, Tokyo 152-8552, Japan  Recent progress in the fabrication technology of silicon nanostructures has made possible observations of novel electrical and optical properties of silicon quantum dots, such as single electron tunneling, ballistic transport, visible photoluminescence and electron emission. Nanocrystalline silicon particles with size less than 10 nm have been prepared by VHF plasma decomposition of silane gas. Pulsed gas plasma processing, in which the nucleation and the growth period are controlled precisely, is turned out to be effective for the preparation of monodispersed nanocrystalline silicon particles [1]. Electrical properties of nanocrystalline silicon particles have been investigated by employing nanoscale electrodes, both planar [2] and vertical [3] configurations, prepared by electron-beam lithography. Coulomb blockade and Coulomb oscillations predominantly due to a single quantum dot are readily modeled as well as interactions of electrons between neighboring dots. Single-electron memory effects are studied using a short channel MOSFET having Si quantum dots as a floating gate [4]. Oxidation process of nanocrystalline Si particles is studied intensively in order to fabricate Si dots with size less than 5 nm. Visible photoluminescence [5] and high-efficiency electron emission [6] have been observed from surface oxidized nanocrystalline silicon particles. We have proposed a novel material NeoSilicon in which both particle size and interparticle distance of nanocrystalline silicon (nc-Si) quantum dots are precisely controlled [7].  We developed a method of making the nc-Si dot dispersion solution and assembling the nc-Si dots from the solution by using the drop & evaporation technique. Methanol was found to work best as a suitable solvent for nc-Si dots. The nc-Si dots were assembled successfully in the two-dimensional manner on the hydrophilic SiO2 surface via the lateral capillary meniscus force. By making the evaporation process slower with use of isopropanol as a solvent, densely packed layered structures were formed with an areal dot density as high as 9.4×1011 dots/cm2. In addition, we examined the assembly of the nc-Si dots on the patterned SOI substrates with nanoscale electrodes with a gap of as small as 20 nm and succeeded in fabricating the nc-Si dots cluster bridging between the electrodes. Combining the top-down nanolithography and bottom-up self-assembly, this technique may provide a new method to fabricate nanoscale Si structures for the future quantum information device applications.  References  1.  T. Ifuku, M. Otobe, A. Itoh and S. Oda, “Fabrication of Nanocrystalline Silicon with Small Spread of Particle Size by Pulsed Gas Plasma” Jpn. J. Appl. Phys., 36, 4031-4034 (1997). 2.  A. Dutta, S. Oda, Y. Fu and M. Willander, “Electron Transport in Nanocrystalline-Si Based Single Electron Transistors,” Jpn. J. Appl. Phys., 39(7B), 4647-4650 (2000). 3.  K. Nishiguchi and S. Oda, “Electron transport in a single silicon quantum structure using a vertical silicon probe,” J. Appl. Phys., 88 (7), 4186-4190 (2000). 4.  B. J. Hinds, T. Yamanaka and S. Oda, “Emission Lifetime of Polarizable Charge Stored in Nano-Crystalline Si Based Single Electron Memory” J. Appl. Phys., 90 (12), 6402-6408 (2001). 5.  K. Arai, J. Omachi, K. Nishiguchi and S. Oda, “Photoluminescence study of the self-limiting oxidation in nanocrystalline silicon quantum dots” Mat. Res. Soc. Symp. Proc., 664, A20.6 (2001). 6.  K. Nishiguchi, X. Zhao and S. Oda, “Nanocrystalline silicon electron emitter with a high efficiency enhanced by a planarization technique” J. Appl. Phys., 92 (5), 2748-2757 (2002). 7.  S. Oda, “NeoSilicon materials and silicon nanodevices” Materials Science and Engineering B, 101, 19-23 (2003).                                      Fig.  2. A schematic flow-chart of the drop & evapolation process.                                    (a)                                    (b) Fig. 4.  SEM images of the nc-Si dots assembled at room temperature with the drop & evaporation method using methanol solvent on Si (a) and SiO2 (b) substrates.               Fig. 5.  The nc-Si dots assembled by using the drop & evaporation method using isopropanol solvent on the SiO2 substrate. The observed steps were probably formed when two (or multiple) assembled flat regions were pushed against each other by the lateral capillary force. The conditions on evaporation should be optimized for further improvement of the assembly process.            depositionultrasonic treatment for 5min in a solvent drop& evaporation 100nm200nm 30nm  300nm 200nm 100nm SiH4ArSubstratePlasma CellUHVChamberVHF(144MHz) PC controlSiH4ArSubstratePlasma CellUHVChamberVHF(144MHz) PC control  Fig.  1. A schematic diagram of the fabrication system of nanocrystalline silicon dots using plasma cells and a TEM image of a nc-Si dot.                    (a)                                    (b)  Fig. 6.  SEM image of the nc-Si dots assembled on the SOI wafer with patterned nanoelectrodes (a) and the blow-up of the nanogap region (b).  Fig.  3. SEM image of the nc-Si dots assembled with the drop & evaporation method. 10nm 10nm

Electron transport in a single silicon quantum structure using a vertical silicon probe,”

Nanocrystalline silicon electron emitter with a high efficiency enhanced by a planarization technique”

NeoSilicon materials and silicon nanodevices”

Photoluminescence study of the self-limiting oxidation in nanocrystalline silicon quantum dots”

Formation of nanocrystalline silicon quantum dot arrays

Formation of nanocrystalline silicon quantum dot arrays

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