Direct Measurement of Coherency Limits for Strain Relaxation in Heteroepitaxial Core/Shell Nanowires
Direct Measurement of Coherency Limits for Strain Relaxation in Heteroepitaxial Core/Shell Nanowires
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DOI：
10.1021/nl3022434
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发表时间：
2013-05-01
期刊：
影响因子：
10.8
通讯作者：
Picraux, S. Tom
中科院分区：
文献类型：
--
作者：
Dayeh, Shadi A.;Tang, Wei;Picraux, S. Tom
纳米级异质外延应变半导体的生长使得能够定制材料特性以增强器件性能。对于核/壳纳米线（NW），理论预测的一致性限制和它们所携带的影响仍然不确定，没有适当的识别应变松弛的机制。我们在这里提出的Ge/Si核/壳NW系统的第一个实验测量的临界壳厚度的应变松弛在半导体NW异质结构和识别的松弛机制。轴向和切向应变消除是通过< 110 >在{111}滑移面上的成核和滑移形成周期性的α/2完美位错而开始的。位错段的滑移通过实时原位透射电子显微镜观察和位错动力学模拟直接证实。进一步的壳生长导致粗糙化和晶粒形成，这提供了额外的应变消除。作为核/壳应变共享的结果，在NW中，一个16 nm半径的锗NW与3 nm的硅壳被示出为容纳3%的相干应变在平衡，一个因素的3增加超过1 nm的平衡临界厚度的平面Si/Ge异质外延生长。
The growth of heteroepitaxially strained semiconductors at the nanoscale enables tailoring of material properties for enhanced device performance. For core/shell nanowires (NWs), theoretical predictions of the coherency limits and the implications they carry remain uncertain without proper identification of the mechanisms by which strains relax. We present here for the Ge/Si core/shell NW system the first experimental measurement of critical shell thickness for strain relaxation in a semiconductor NW heterostructure and the identification of the relaxation mechanisms. Axial and tangential strain relief is initiated by the formation of periodic a/2 < 110 > perfect dislocations via nucleation and glide on {111} slip-planes. Glide of dislocation segments is directly confirmed by real-time in situ transmission electron microscope observations and by dislocation dynamics simulations. Further shell growth leads to roughening and grain formation which provides additional strain relief. As a consequence of core/shell strain sharing in NWs, a 16 nm radius Ge NW with a 3 nm Si shell is shown to accommodate 3% coherent strain at equilibrium, a factor of 3 increase over the 1 nm equilibrium critical thickness for planar Si/Ge heteroepitaxial growth.