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We observe room temperature Coulomb staircases in the current-voltage characteristics of single Si nanochain devices. The Si nanochains are synthesized by thermal evaporation of a SiO powder solid source at 1400°C in a quartz tube furnace [1]. The nanochains consist of silicon nanocrystals (SiNCs) separated by SiO2 ‘necks’. The SiNC diameter varies from ~10 nm to ~30 nm, and the separation varies from ~15 nm – 40 nm. A thin SiO2 layer, ~1 nm – 3 nm thick, exists on the SiNC outer surface.
The devices are fabricated on silicon-on-insulator (SOI) material with a ~50 nm thick SiO2 capping layer. The top Si layer of the SOI material forms a conducting back plane. Initially, an array of Cr/Au alignment marks was fabricated by e-beam lithography on the SiO2 capping layer. Nanochain material from the furnace, dissolved in IPA (0.1 mg / 3 ml IPA) using ultrasonic tip agitation, was then spun onto the sample at 5000 rpm. Individual nanochains were then selected with reference to the alignment marks, by scanning electron microscope inspection. Finally, 20 nm Ti / 75 nm Al contacts were evaporated on to the nanochain, after wet etching of the SiO2 layer around the nanochain in the contact regions.
The I-V characteristics of the devices were measured in vacuum (~10-6 mBar) using a needle prober. Multiple- step Coulomb staircases [2] are observed in the I–V characteristics for positive bias in these devices. Each nanochain forms a multiple-tunnel junction (MTJ) [2], with tunnel barriers formed at the SiO2 regions. Ti/Al contacts are fabricated to selected nanochains to create single nanochain devices. Single-electron charging occurs in the MTJ, leading to multiple-step Coulomb staircase characteristics at 300 K. Single-electron charging energy ~0.38 eV ~ 14kBT at 300K. The characteristics may be attributed to charge soliton-like transport in the MTJ [2].
[1] H. Y. Peng, N. W. Wang, W. S. Shi, Y. F. Zhang, C. S. Lee and S. T. Lee, J. Appl. Phys., 89, 727 (2001); A. Colli, A. C. Ferrari, S. Hofmann, J. A. Zapien, Y. Lifshitz, S. T. Lee, S. Piscanec, M. Cantoro, and J. Robertson, AIP Conf. Proc. 723, 445 (2004).
[2] H. Grabert, and M. H. Devoret, (Eds.), Single Charge Tunneling – Coulomb Blockade Phenomena in Nanostructures, NATO ASI Series B, Plenum Press, (1991).
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