Fabrication and electron transport properties of two-dimensionally-coupled dots of single crystalline Si

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In this work, we fabricated single-crystalline Si dots on SiO_2 with a high density (two-dimensionally-coupled Si dots) and investigated the transport properties based on the single electron tunneling.The coupled Si dots were fabricated using a nanometer-scale selective oxidation technique developed by our group. In this technique, naturally-formed SiN islands as small as 10 nm in lateral size are used as the oxidation mask. Although the thickness of the SiN islands is only 0.5 nm, the oxidation is strongly prevented below the SiN islands. Applying this technique to an SOI (silicon-on-insulator : thin Si layer is formed on SiO_2), the SOI layer is converted to the Si dots. Here, the size and interspacing of the dots depend on the SiN masks, i.e., the condition of the nitridation. The electrical coupling between the dots is controlled by the thickness of Si sheet remaining between the dots, which is determined by the oxidation time. The thin Si sheet should work as the tunneling barrier because the expansion of the band gap occurs due to the formation of the discrete levels resulting from the quantum mechanical effect.For the current-voltage (I-V) measurements, an FET structure with a channel of the coupled Si dots was formed. In the I-V measurements performed at 15K, we observed the oscillatory behavior, so-called Coulomb oscillation. This is the direct evidence for the single electron tunneling effect. We are now trying to interpret the I-V data as well as to observe the transport path of a single electron in situ by Kelvin probe force microscopy (KFM).