Study of Strain Relaxation Mechanisms of Semiconductor Nanostructures by means of Atomistic Simulation

1.采用Stillinger-Weber势和Tersoff势的分子动力学模拟方法研究了Si和Ge原子在Si衬底上沉积的行为以及沉积层的初始形貌与衬底温度的关系.对于Si/Si均质淀积工艺，得到的结论是：（1）在300 K和400 K时，淀积层形成非晶结构;（2）在700 K和1000 K时，淀积原子在连续原子层中构成交替垂直的二聚体行，形成外延结构，这与实验结果一致，（3）单个原子在300 K和400 K下的沉积轨迹范围不超过基片表面最近邻原子之间的长度，500 K下的沉积轨迹范围约为，700 K和1000 K下的沉积轨迹范围超过基片表面最近邻原子之间的长度，这对应于在这些温度下沉积层的不同形态。对于Ge/Si异质沉积工艺 ...更多信息 结果表明：（4）在1000 K时，沉积能量为0.2eV时，沉积层以逐层模式生长，直到最初的2 ~ 4个单层膜沉积完成，然后转变为非晶模式，而在其它条件下，沉积层形成非晶结构.采用Tersoff势的分子动力学模拟方法研究了Si/Ge/Si量子点结构中应变分布的温度依赖性，得到了光模的声子态密度.结果表明：（1）在有限温度下，用分子动力学方法计算的量子点内部的应变分布与共轭梯度法计算的结果定性一致，尽管前者垂直于量子点底部的法向应变分量大于后者，以及（2）量子点中的光学模式的声子态密度的峰的位置从块体晶体中的声子态密度的峰的位置偏移3。采用分子动力学模拟方法研究了碳纳米管的力学性能。用Brenner势计算了碳原子间的相互作用。得到了具有相同直径和六个手性角的纳米管模型的泊松比和杨氏模量。结果表明：（1）纳米管的泊松比取决于其手性角;（2）纳米管的杨氏模量不取决于其手性角;（3）纳米管的弹性变形区非常宽。少

1. How the behavior of a Si adatom or a Ge adatom deposited on the Si substrate and the morphology of the deposited layers in the initial period depend on the substrate temperature was investigated by the molecular-dynamics simulations with the Stillinger-Weber potential and the Tersoff one. For Si/Si homo-deposition processes, it was concluded that (1) the deposited layers form an amorphous structure at 300K and 400K, (2) the deposited atoms construct the alternately perpendicular dimer rows in the successive atomic layers to form an epitaxial structure at 700K and 1000K, which agrees with experimental results, (3) the ranges of the trajectories of a single deposited atom at 300K and 400K do not extend beyond, those at 500K are of the order of, and those at 700K and 1000K extend beyond the length between the nearest-neighbor atoms at the substrate surface, which corresponds with the different morphologies of the deposited layers at the temperatures. For Ge/Si hetero-deposition process … More es, it was elucidated that (4) at 1000K, the deposited layers with the deposition energy 0.2eV grow in the layer-by-layer mode until the initial two to four monolayers are deposited, and then the growth mode changes into the amorphous one while the deposited layers form amorphous stractures in the other conditions.2. The temperature dependence of the strain distributions within Si/Ge/Si quantum dot structures was investigated using the molecular-dynamics simulation with the Tersoff potential, and the phonon densities of states for the optical mode were obtained. It was concluded that (1) the strain distributions within quantum dots computed by the molecular-dynamics method, at finite temperatures qualitatively agree with those computed by the conjugate-gradient method although the normal strain components perpendicular to the base of the quantum dots to the former are larger than those in the latter, and that (2) the positions of the peaks of the phonon densities of states for the optical mode in the quantum dots shift from those in bulk crystals3. The mechanical properties of carbon naotubes were investigated by the molecular-dynamics simulation. The interaction between carbon atoms were calculated by using the Brenner potential. The Poisson's ratios and the Young's modulus were obtained for the naotubes models with the same diameter and with six chiral angles. It was conluded that (1) the Poisson's ratios of naotubes depend on their chiral angles, (2) the Young's modulus of nanotubes does not depends on their chiral angles, and (3)the elastic region in the deformations of nanotubes are extremely broad. Less