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Formation and nano-scale characterization of ultrahigh-density nanodot superlattices

超高密度纳米点超晶格的形成和纳米级表征

基本信息

批准号：
15201023
负责人：
ICHIKAWA Masakazu
金额：
$ 31.45万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2006
项目状态：
已结题

项目摘要

Semiconductor nanostructures have attracted much interest due to their quantum-confinement effects, which can cause changes in material opto-electronic properties. We found that ultra-small Ge nanodots with the size of ~5 nm and ultra-high density of ~10^<12> cm^<-2> grew on Si surfaces covered with ultrathin SiO_2 films (~0.3nm thickness). Deposited Ge atoms on the surfaces reacted with the ultrathin SiO_2 films by the chemical reaction of SiO_2+Ge→SiO↑ + GeO↑ to form Ge nanodot nucleation sites. The following deposited Ge atoms were mainly captured by the nucleation sites due to the larger adsorption energy on the nucleation sites than that on the SiO_2 films. This resulted in Ge nanodot formation with ultra-small and uniform size and with ultra-high density. Ge nanodots had spherical shape which was different from that of the Ge island formed by the Stranski-Krastanov growth. Epitaxial or non-epitaxial Ge nanodots could be formed on the substrates by changing substrate temperatures … More during Ge deposition. The ultrathin SiO_2 technolgy could also been applied to form different kinds of nanostructures such as Si nanodots and β-FeSi_2 nanodots or nanoislands.We investigated electronic properties of individual Ge nanodots by scanning tunneling spectroscopy. With decreasing the dot size, the energy band gap of Ge nanodots increased to ~1.4 eV with the size change from 7 to 2 nm, which could be explained by the carrier quantum-confinement effect in Ge nanodots. We also observed the Coulomb-blockade effect featured by discrete tunneling current fluctuation on Ge nanodots at room temperature. The discrete fluctuation was explained by a single electron trap in a nanodot and a single electron escape into Si substrate. We further investigated the optical properties of the stacked structures in which Ge nanodots were embedded in Si films. Intense photoluminescence and electroluminescence were observed at photon energies around 0.8 eV (~1.5 μm) from the structures after high-temperature annealing. The photon energies around 0.8 eV are widely used for the optical communication.We also developed cathode-luminescence and electroluminescence systems using scanning tunneling microscopy to investigate optical properties of an individual nanodot. Less

半导体纳米结构由于其量子限制效应而引起材料光电特性的变化，引起了人们的广泛关注。我们发现在覆盖有SiO_2薄膜（厚度约为0.3nm）的Si表面上生长出了尺寸约为5 nm、密度约为10^ cm ~ 2的超小Ge纳米点<12><-2>。沉积在表面的Ge原子与SiO_2薄膜发生SiO_2+Ge→SiO↑ + GeO↑的化学反应，形成Ge纳米点成核位置。由于成核位置上的吸附能大于SiO_2膜上的吸附能，后续沉积的Ge原子主要被成核位置捕获。这导致形成具有超小且均匀尺寸和超高密度的Ge纳米点。Ge纳米点具有球形形状，这不同于由Sttranski-Krastanov生长形成的Ge岛。通过改变衬底温度，可以在衬底上形成外延或非外延Ge纳米点 ...更多信息在Ge沉积期间。SiO_2纳米技术还可以用来制备不同的纳米结构，如Si纳米点和β-FeSi_2纳米点或纳米岛。随着Ge纳米点尺寸的减小，Ge纳米点的能带隙增大到~1.4 eV，尺寸从7 nm变化到2 nm，这可以用Ge纳米点中的载流子量子限制效应来解释。我们还观察到室温下Ge纳米点上以离散隧穿电流波动为特征的库仑阻塞效应。用纳米点中的单电子陷阱和单电子逃逸到Si衬底中解释了这种离散的涨落。我们进一步研究了Ge纳米点嵌入Si薄膜的堆叠结构的光学性质。高温退火后，在光子能量约为0.8eV（~1.5 μm）处观察到强烈的光致发光和电致发光。光子能量在0.8eV左右的光子被广泛应用于光通信。我们还开发了阴极发光和电致发光系统，使用扫描隧道显微镜来研究单个纳米点的光学性质。少