Self-Assembling Formation of Silicon Quantum Dots

采用低压化学气相沉积（LPCVD）技术，在525 ~ 650℃的温度范围内，在热生长SiO_2/ C -si表面自发形成纳米级硅点。采用原子前显微镜（AFM）和透射电镜（TEM）观察了硅点的尺寸分布和面积密度。SiH_4的热分解作用和吸附在SiO_2上的前驱体在Si成核部位的内聚作用分别限制了SiO_2表面的Si点直径和高度。在氧端SiO_2表面形成Si点时，成核密度显著提高，从而使Si点的尺寸和分布变小。采用导电AFM探针测量了SiO_2/ si点/SiO_2双势垒结构的隧穿电流。结果表明，在室温下可以清楚地看到负电导特性，表明谐振隧穿发生在单个Si量子点上。在室温下，SiO_2覆盖的Si量子点具有较高的发光效率。在光子能量为2.54和3.81eV的激发下，没有观察到发光峰值能量和光谱形状的差异。结果表明，发光主要来源于光学带隙小于2.54eV的Si点。

Nanometer-size silicon dots were spontaneously formed on thermally-grown SiO_2/c-Si by low-pressure chemical vapor deposition (LPCVD) of pure silane (SiH_4) in the temperature range from 525 to 650ﾟC.The size distribution and the area density of Si dots were evaluated by using atomic fore microscopy (AFM) and transmission electron microscopy (TEM). The Si-dot diameter and dot height on as-grown SiO_2 are rate-limited by the thermal decomposition of SiH_4 and the cohesive action of adsorbed precursors on Si nucleation sites, respectively. It has been also found that in the Si dot formation on OH-terminated SiO_2 surface the nucleation density is dramatically enhanced and consequently the dot size and its distribution become small. The tunneling current through SiO_2/Si-dot/SiO_2 double barrier structures was measured by using a conducting AFM probe. As result, negative conductance characteristics are clearly seen at room temperature, indicating that the resonant tunneling occurs through a single Si quantum dot. It was also demonstrated that Si quantum dots covered with SiO_2 exhibit high efficiency luminescence at room temperature. No differences in luminescence peak energy and spectral shape are observable between excitations with a photon energy of 2.54and 3.81eV.It is suggested that the luminescence mainly originates from Si dots whose optical bandgap are under 2.54eV.