Structural relaxation in Si and Ge nanocrystallites: Influence on the electronic and optical properties
Structural relaxation in Si and Ge nanocrystallites: Influence on the electronic and optical properties
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Si 和 Ge 纳米晶的结构弛豫：对电子和光学性质的影响
DOI：
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发表时间：
2003
期刊：
影响因子：
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通讯作者：
F. Bechstedt
中科院分区：
文献类型：
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作者：
H.;J. Furthmüller;F. Bechstedt
通过从头计算，发现了直径在10 ~ 25 AA{}之间的氢饱和锗和硅纳米晶体的复杂原子弛豫模式。当纳米晶体中心的键在相应的块状材料中扩展超过其长度时，表面附近的键被缩短。平均键长减小。表面的原子向内移动，边缘和角落的原子向外移动，使晶体的体积几乎保持不变。作为结构松弛的结果，与各自理想结构的值相比，对激发能增加，并且Ge比Si更强。对整体吸收光谱的主要影响是不同光谱特征的上移。对于锗晶体来说，最重要的是在HOMO-LUMO（最高占据的分子轨道-最低未占据的分子轨道）间隙附近电子态的能量顺序的变化，导致它们的辐射寿命下降了几个数量级。
A complex atomic relaxation pattern for hydrogen-saturated Ge and Si nanocrystallites with diameters between 10 and 25 AA{} has been found by means of ab initio calculations. While the bonds at the center of the nanocrystals expand beyond their length in the corresponding bulk material, the bonds near the surface are shortened. The average bond lengths decrease. The atoms at the surface facets move inward, those at the edges and corners outward, leaving the volume of the crystallite almost unchanged. As a consequence of the structural relaxation, the pair excitation energies increase as compared to the values for the respective ideal structures, and they do so stronger for Ge than for Si. The main effect on the overall absorption spectra is an upward shift of the different spectral features. Most important for Ge crystallites is the change of the energetic ordering of the electronic states close to the HOMO-LUMO (highest occupied molecular orbital--lowest unoccupied molecular orbital) gap, leading their radiative lifetimes to decrease by orders of magnitude.