硅基低维结构的电子态和光学性质

Canham的文章发表以后，引起了世界范围的研究热潮，目的是实现硅基的集成光电子技术．其中一个主要的研究方向是多孔硅的发光机制．根据各自的实验结果提出了不同的模型：量子限制、表面态复合、硅氧烷及其衍生物、以及声子辅助跃迁等．同时开始了理论计算，方法包括：紧束缚、经验赝势、和基于局域密度泛函的第一原理方法等．大部分理论计算研究的是量子限制对多孔硅和纳米硅晶发光的效应．计算得到的辐射寿命比直接能隙GaAs中激子的长得多，说明量子限制不能完全解释多孔硅的高发光效率．提出了一个经验赝势的同质结模型来计算多孔硅和纳米硅晶的电子结构．多孔硅的波函数用一组体Si波函数展开，它们的波矢满足周期性边界条件．利用简并微扰论计算了S量子线、量子孔、量子阱层和棱柱晶粒的电子态和光跃迁几率(寿命)．用紧束缚集团模型研究了表面键饱和对Si纳米晶体发光的效应．取表面Si原子的悬键与吸附原子之间的相互作用能量Vs为不同的值，代表不同的吸附原子．发现当Vs的绝对值变小时，能隙减小，同时跃迁几率增加约2个数量级．

Electronic States and Optical Properties of Silicon-based Low Dimensional Structures

Canham's paper~() generated worldwide speculation that a silicon-based optoelectronic technology was at hand, and it kicked off a flurry of research activities directed at porous silicon. A large effect was spent in clearing the luminescence mechanism of porous silicon. Several models were proposed according to various experimental results: quantum confinement model, surface state recombination model, siloxene derivatives model, and phonon assistant transition model, etc.Theoretical calculations started from 1992, ranging from tight binding, empirical pseudopotential, to sophisticated first-principle approaches based on the local density approximation. Most of theoretical researches studied the quantum confinement effect on the luminescence of porous Si and Si nanocrystallites. The calculated radiative lifetime is much longer than that of excitons in the direct-gap GaAs, suggesting that the quantum confinement effect cannot completely explain the high radiative efficiency of porous Si.We proposed an empirical pseudopotential homojunction model to calcuate the electronic structure of porous Si and Si nanocrystallites. The wave functions of porous Si are expanded by the bulk Bloch states with the wave vectors satisfying the periodic boundary condition. Using the degenerate perturbation theory we calculated the electronic states and transition probabilites (lifetime) for Si quantum wires, pores, slabs, and prisms.We also studied the effect of the surface-bond saturation on the luminescence of Si nanocrystals by using the tight-binding cluster model. The interaction energies betwen dangling bonds of Si atoms at the surface and the absorption atoms V_s are taken as various values, representing different absorption atoms. It is found that when the absolute value of V_s becomes smaller, the energy gap decreases, and the transition probability increases by about two orders of magnitude.