Stability of misfit dislocations in axial-heteroepitaxial nanopillar structures

异质外延系统允许将联合收割机不同的半导体材料组合成功能器件，这些功能器件由于多功能的电子、光学和热电特性而脱颖而出。通过将材料尺寸缩小到纳米级，可以避免或至少减少在这样的系统中形成失配相关的晶格缺陷，从而显著增强可应用的材料调色板以及相应器件的应用范围和寿命。然而，特别是在纳米棒的轴向面上的异质外延层的情况下，还没有很好地理解什么时候失配位错的配置是晶体学稳定的。因此，本项目解决了通过纳米球光刻在衬底晶体上创建GaAs柱纳米结构，通过使用分子束外延在柱顶部生长失配InAs层，然后通过实验和理论分析失配位错稳定性。最重要的是，要建立一个模型，可靠地预测的临界尺寸之间的过渡的相干和半相干状态，考虑现实的标本形态。此外，应确定限制平衡位错组态，重点是位错位置和类型，以及异质界面的有限化学宽度的影响。

Heteroepitaxial systems permit to combine different semiconductor materials into functional devices, which stand out due to versatile electronic, optic and thermoelectric properties. By scaling the material dimensions down to the nanoscale, the formation of misfit related lattice defects can be avoided or at least reduced in such systems, thus considerably enhancing the applicable materials palette as well as range of applications and lifetime of corresponding devices. However, especially in the case of heteroepitaxial layers on the axial face of nanorods it is not yet well understood when misfit dislocations in which configuration are thermodynamically stable. Therefore, the present project addresses the creation of GaAs pillar nanostructures on substrate crystals by means of nanosphere lithography, the growth of mismatched InAs layers on top of the pillars by using molecular beam epitaxy, followed by experimental as well as theoretical analysis of misfit dislocation stability. Most importantly, a model is to be established that reliably predicts the critical dimensions for the transition between the coherent and the semicoherent state by considering realistic specimen morphologies. Furthermore, the restricted-equilibrium dislocation configuration with emphasis on dislocation position and type, and the influence of the finite chemical width of the hetero-interface shall be determined.