Control of Silicon quantum structures and its application to room-temperature device operation

研究了硅烷(SiH_4)低压化学气相沉积(CVD)在超薄SiO_2表面自组装形成硅量子点(SiQD)的过程，提出了SiQD的形成机理，并提出了一种控制SiQD排列的实用方法。此外，对于覆盖很薄SiO_2的多层SiQD，在室温下测量了比非线性电导及其随时间的变化。本研究的主要结果和成果如下：(1)由于SiH_4-LPCVD中SiH_2表面的Si-OH键作为反应中心，因此Si-OH键的位置控制使我们能够控制SiO_2上SiQD的排列。(2)由于碳氢化合物和/或水分子的物理吸附，表面污染严重退化了Si点排列的区域选择性成核，这在清洁空气中是不可避免的。(3)使用扫描探针显微镜(如…)的表面修饰技术更多的FM或STM被用来有意地在SiO_2表面的某个位置或区域形成Si-OH键。基于这些技术，开发了一种无污染的选择性成核工艺，实现了高选择性生长和精确定位硅量子点。(4)用AFM同时测量的形貌和电流图像表征了夹有超薄SiO_2层的硅量子点阵列的双势垒结构，结果表明，硅量子点的共振隧穿不仅与点的大小有关，而且与相邻点之间的电荷差异有关。(5)用开尔文探针模式操作原子力显微镜针尖，通过测量局部表面电势的变化，可以得到进入硅量子点的电子荷入量。(6)研究了通过重复点形成和表面氧化制备的覆盖SiO_2的多层硅量子点的电子输运，并测量了在室温下通过耦合硅量子点的隧穿电流中明显的随机电报噪声(RTN)。RTN中的偏置电压与频率和电流变化的关系表明，观察到的RTN现象可以用耦合量子点隧道路径附近的电子充放电来解释。较少

Self-assembling formation of silicon quantum dots (SiQDs) on ultrathin SiO_2 by low pressure CVD using silane (SiH_4) has been studied, and the formation mechanism for positioning SiQDs has been proposed and a practical process to control the arrangement of the SiQDs has been developed. In addition, for multiply-stacked SiQDs covered with very thin SiO_2, specific non-linear conductance and its temporal variation have been measured at room temperature. The major results and achievements of this research are as follows :(1) Since Si-OH bonds on the SiO_2 surface act as reactive sites in SiH_4-LPCVD, the position control of the Si-OH bonds enables us to control the arrangement of the SiQDs on SiO_2.(2) Area-selective nucleation for the Si dot arrangement is degraded seriously by surface contamination due to physisorption of hydrocarbons and/or water molecules, which is inevitable in exposure to clean room air.(3) Surface modification techniques using a scanning probe microscope such as A … More FM or STM have been applied to form the Si-OH bonds out the SiO_2 surface intentionally at a certain position or area. Based on these techniques, a contamination-free process for the selective nucleation has been developed to realize highly-selective growth and precise positioning of the SiQDs.(4) The double barrier structures of a SiQDs array sandwiched with ultrathin SiO_2 layers have been characterized by simultaneously-measured AFM topographic and current images, The results show that the resonant tunneling through each of the SiQDs depends on not only the dot size but also the difference in electron charging among the neighboring dots.(5) The amount of electron charging into the SiQDs can be derived from the change in the local surface potential measured by operating an AFM tip with a Kelvin probe mode.(6) The electron transport through multiply-stacked SiQDs covered with SiO_2, which were prepared by repeating the dot formation and the surface oxidation, has been studied and distinct random telegraph noise (RTN) in tunneling current, through coupled SiQDs has been measured even at room temperature. The bias voltage dependence of the frequency and the current variation in the RTN suggests that the observed RTN phenomenon can be interpreted in terms of electron charging and discharging in the dots being the neighbor of the tunneling path for coupled quantum dots. Less