【作者】 荆宇航；

【导师】 张少实； 孟庆元；

【作者基本信息】 哈尔滨工业大学 ， 固体力学， 2007， 硕士

【摘要】 随着对Si基半导体器件速度和功率要求的不断提高,使用应变方法进行人工能带剪裁的技术显得越来越重要。在Si基体与外延的Si_1-xGe_x层之间加入一层相对低温条件下生长的低温Si（LT-Si）层,该层中大量存在的各种类型缺陷改变了失配应变的释放机理,最终得到了高质量的Si_1-xGe_x层。这种方法在这近十年间被广泛的研究和不断改进,Si_1-xGe_x层质量也不断的提高。但是,对于这种方法机理的解释,却始终没有一个统一的认识。SiGe/Si结构的失配应力的释放主要是通过在{111}面上生成可以滑动的60度位错来完成的,本文采用分子动力学的模拟方法,使用Stillinger-Weber势函数和周期性边界条件,建立了60度位错偶极子,具体研究点缺陷和60度位错的相互作用。首先提出了相对简单的建立位错偶极子的新方法:把混合型位错分解为刃位错和螺位错分量,依次加载原子的位移场,得到初始构型,再执行模拟退火过程以稳定位错芯结构。通过计算发现,在位错芯附近的空位及自间隙原子的形成能要比远离位错芯或者没有位错缺陷完整晶体的形成能低。其次使用Parrinello-Rahman方法施加剪切应力,研究了位错在相当于晶格失配应力作用下的运动情况。与空位缺陷及自间隙原子缺陷作用后的位错,其运动速度要比完好的位错速度慢,位错速度随着剪应力增大而增加,随着温度升高而降低,这一结果与声子拖拽模型相吻合,但与缺陷作用后的位错运动的声子拖拽效应更加明显。同时发现,派纳力随着温度升高而降低,这与Peierls–Nabarro model相一致,相比之下,与缺陷作用后的位错的派纳力增加很多。由此可以推断出,低温硅（LT-Si）缓冲层中点缺陷对失配位错运动具有阻碍作用。更多还原

【Abstract】 With the demand of the speed and power of Si based semiconductor devices, the technology of band tailoring via stress is becoming more and more important. When putting a layer of Si buffer grown in low temperature between the SiGe epi-layer and Si substrate, there are large amount and kinds of defects in the buffer layer that alter the strain relaxation mechanism and make the final threading dislocation density very low. This method is studied widely and improved constantly in these 10 years, and the quality of Si_1-xGe_x layer is improved constantly. But the relaxation mechanism of this method is still under debate.Because the relief of lattice misfit stress is mainly depending on the glide of 60o dislocation on the {111} plane, a 60°dislocation dipole model was built by molecular dynamics simulation method based on the Stillinger-Weber potential and periodic boundary condition, point defect interaction with dislocation was investigated concretely.Firstly, a relatively simple method was presented to generate a dislocation dipole: divide the mixed dislocation into the edge and screw components, impose a displacement field to all atoms to establish the initial configuration, and then conduct a simulated annealing process for relaxation. Calculated formation energies of vacancies and self-interstitials near the core of a 60°dislocation are considerably lower than in the bulk.Secondly, the dislocation motion characteristics under lattice misfit stress are studied with Molecular Dynamics, the shear stress is applied with Parrinello-Rahman method. The velocity of dislocation interaction with vacancies and self-interstitials is slower than that of perfect dislocation, the velocity of dislocation increases as the stress increases, decreases as the temperature increases, which is consistent with the phonon drag model. It is more obvious that the phonon drag mechanism enhances during the motion of dislocation interaction with defects. The peierls stress decreases as the temperature increases, which is consistent with the Peierls–Nabarro model, and the peierls stress of dislocation interaction with defects increases largely. It can be concluded that the defects in the low temperature Si buffer will block the motion of misfit dislocation.更多还原