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SiO_2/Si(100)超晶格结构能带边布洛赫函数的能量色散关系和几率分布。从能带边缘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。结果表明：(1)SiO_2层厚度与价带偏移量和空穴穿透深度的关系：由于SiO_2层的能隙减小，价带偏移量随SiO_2层厚度减小而减小。空穴的穿透深度与价带偏移量(2)硅层厚度对价带偏移量和能隙的依赖关系是一致的：随着硅层厚度的减小，价带偏移量减小，能隙增大。载流子注入对价带偏移量的影响：价带偏移量随着电子浓度的增加而增加，但随着空穴浓度的增加价带偏移量减小。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.