Atomistic tunnelig barrier of heteroepitaxial SiO_2/Si(001)

采用密度泛函第一性原理计算方法，计算了SiO2/Si（100）超晶格结构能带边缘的能量色散关系和Bloch函数的几率分布.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量的计算方法。虽然传统的方法适用于厚层，但即使超晶格的层厚度很薄，这种方法也是可行的。(1)价带偏移和相应的空穴穿透深度的SiO2层厚度依赖性：由于SiO2的能隙减小，价带偏移随着SiO2层厚度减小而减小。（2）价带偏移和能隙的Si层厚度依赖性：随着Si层厚度的减小，价带偏移减小，能隙增大。这是由于Si层中的量子限制效应。(3)价带偏移的载流子注入依赖性：价带偏移随着电子浓度的增加而增加，尽管价带偏移随着空穴浓度的增加而减小。这归因于载流子注入引起的静电势的变化。

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.