Atomistic tunnelig barrier of heteroepitaxial SiO_2/Si(001)

利用密度泛函第一性原理计算方法，计算了SiO2/Si（100）超晶格结构的能带边缘能量色散关系和Bloch函数的概率分布。从带边能量和布洛赫函数的概率分布出发，提出了一种新的价带偏移评价方法。即使超晶格的层厚很薄，也可以使用这种方法，尽管传统方法适用于厚层。得到了以下结果：(1) SiO2层厚对价带偏移量与相应孔穿透深度的依赖关系：由于SiO2的能隙减小，价带偏移量随着SiO2层厚的减小而减小。(2)价带偏移量与能隙的Si层厚度依赖性：随着Si层厚度的减小，价带偏移量减小，能隙增大。这是由于硅层中的量子限制效应。(3)价带偏移对载流子注入的依赖性：价带偏移随电子浓度的增加而增加，但价带偏移随空穴浓度的增加而减小。这是由于注入载流子改变了静电势。

Energy dispersion relation and probability distribution of the Bloch function at the band edge were calculated for SiO2/Si(100) super-lattice structure, using the density functional first-principles calculation. From the band edge energy and the probability distribution of the Bloch function, novel evaluation method of valence band offsets are proposed. This method can be available even if the layer thickness of the super-lattice is very thin, although the conventional method is appropriate for thick layers.The following results have been obtained.(1) SiO2 layer thickness dependence of valence band offsets and corresponding penetration depth of a hole : The valence band offsets decreases as SiO2 layer thickness decreases, due to decrease of the energy gap of SiO2. The penetration depth of a hole gives a consistent result with the valence band offset(2) Si layer thickness dependence of valence band offsets and energy gap : The valence band offset decreases and the energy gap increases, as Si layer thickness decreases. This is due to quantum confinement effect in Si layer.(3) Carrier injection dependence of valence band offsets : The valence band offsets increases as electron concentration increases, although the valence band offset decreases as hole concentration increases. This is attributed to change of the electrostatic potential by carrier injection.