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

本工作利用本课题组开发的纳米尺度选择氧化技术，在SiO_2衬底上制备了高密度的单晶Si点（二维耦合Si点），并研究了其基于单电子隧穿的输运性质。在这种技术中，自然形成的横向尺寸小至10 nm的SiN岛被用作氧化掩模。虽然SiN岛的厚度仅为0.5nm，但是在SiN岛下方强烈地防止了氧化。将此技术应用于SOI（silicon-on-insulator：thin Si layer is formed on SiO_2）中，可将SOI层转化为Si点。这里，点的尺寸和间距取决于SiN掩模，即，氮化的条件。点之间的电耦合由点之间保留的Si片的厚度控制，该厚度由氧化时间决定。由于量子力学效应导致的分立能级的形成，使带隙发生了扩展，因此薄Si片可以作为隧穿势垒。对于电流-电压（I-V）测量，形成了具有耦合Si点沟道的FET结构。在15 K的I-V测量中，我们观察到了库仑振荡。这是单电子隧穿效应的直接证据。我们现在正试图解释的I-V数据，以及观察一个单一的电子在原位的开尔文探针力显微镜（KFM）的传输路径。

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).