动力学蒙特卡罗法模拟Si（100）基Ge纳米岛的生长

发布时间：2018-08-11 16:53

【摘要】：半导体量子点在纳米电子学、纳米光子学和光电子学等领域具有相当广泛的应用前景,基于量子点的固态量子器件在量子信息技术中将扮演重要角色。Ge/Si量子点由于具有与大规模集成电路相兼容的特点,成为研究的热点之一。为深入理解生长因素及应变对量子点形成的影响,动力学蒙特卡罗方法(KMC)被广泛应用于量子点生长的研究,并已取得了与实际情况相符的结果。论文采用动力学蒙特卡罗法结合MATLAB编程,模拟了Si(100)基底上生长Ge量子点的初期二维Ge纳米岛成核过程。二维Ge纳米岛是量子点生长的核心,它的状态决定着三维岛状结构量子点的成核位置、尺寸和形貌等结构特性,而二维Ge纳米岛在实验上是难于观察的,因此对二维Ge纳米岛的模拟研究有着重要意义。论文采用200×200的四方形格子,作为Ge量子点生长的Si(100)基底,模拟过程主要考虑原子的沉积与扩散两个过程,而不考虑吸附原子的脱附过程。Ge原子在衬底扩散采用周期性边界条件。首先系统研究了基本生长参数对二维Ge纳米岛的成核位置、尺寸大小和均匀性、密度以及分布有序性等方面的影响。随着生长温度的增加,原子扩散能力增强,二维Ge纳米岛的尺寸增大,密度减小；二维Ge纳米岛在的退火过程中的稳定性,随着退火时间增加,吸附原子的平均扩散几率增加,它们会扩散到势能更低的地方聚集,二维Ge纳米岛尺寸增大,密度减小,观察到Ostwald Ripening过程；随着原子沉积量的增大,二维Ge纳米岛密度先增加后减少,尺寸不断增加,量子点间的距离不断减少,甚至出现岛的连结现象。其次研究了图形衬底上二维Ge纳米岛随生长温度和原子沉积的变化。温度较低时,沉积原子受图形衬底的影响不大,随着温度增加,原子不断在图形衬底中形核成为二维岛,但是在过高的温度下,沉积原子的扩散能力强,会脱离图形衬底的束缚,不利于形成分布有序的量子点阵列；同样原子沉积量过小或过大都不利于有序量子点阵列的制备,过小使得量子点尺寸不均匀,过大会破坏有序性。最后研究了生长停顿和沉积原子能量对图形衬底上量子点生长初期的表面形态、岛尺寸分布及空间分布等方面的影响。研究发现,在所选取的停顿时间范围内,时间越长,二维Ge纳米岛的有序性和均匀性越好：停顿次数的增加,会提高原子的扩散能力,因此停顿次数适中时可以获得有序均匀的二维Ge纳米岛阵列,最佳停顿次数为3次；沉积原子的剩余能量的增加,可使图形衬底上二维Ge纳米岛的分布更加有序,尺寸也更均一,这是沉积原子得到适当扩散的结果。通过对Si基底上二维Ge纳米岛的生长模拟,分析了量子点生长的物理机制,得到了生长优质Ge量子点的工艺参数。为获得空间有序的量子点阵、调整和优化制备工艺提供了重要的理论依据。
[Abstract]:Semiconductor quantum dots have a wide range of applications in the fields of nano-electronics, nano-photonics and optoelectronics. Solid state quantum devices based on quantum dots will play an important role in quantum information technology. Ge- / Si quantum dots have become one of the hotspots for their compatibility with large scale integrated circuits (LSI). In order to understand the effect of growth factors and strain on the formation of quantum dots, the kinetic Monte Carlo method (KMC) has been widely used in the study of quantum dot growth. The nucleation process of GE quantum dots grown on Si (100) substrate was simulated by dynamic Monte Carlo method and MATLAB programming. Two-dimensional GE nanoscale island is the core of quantum dot growth. Its state determines the nucleation location, size and morphology of three-dimensional island structure quantum dot, while two-dimensional GE nanoscale island is difficult to observe experimentally. Therefore, it is of great significance to simulate the two-dimensional GE nanoscale island. In this paper, a square lattice of 200 脳 200 is used as the Si (100) substrate grown by GE quantum dots. The simulation process mainly considers the deposition and diffusion of atoms, but not the desorption process of adsorbed atoms. The periodic boundary conditions are adopted for the diffusion of GE atoms on the substrate. The effects of basic growth parameters on the nucleation location, size, uniformity, density and distribution order of two-dimensional GE nanoliths were studied systematically. With the increase of growth temperature, the diffusion ability of atoms increases, the size of two-dimensional GE nanoislands increases and the density decreases, and the stability of two-dimensional GE nanowires during annealing process increases with the increase of annealing time, and the average diffusion probability of adsorbed atoms increases with the increase of annealing time. The density of two-dimensional GE nanowires increases and decreases, and the Ostwald Ripening process is observed. With the increase of atomic deposition amount, the density of two-dimensional GE nanowires increases first and then decreases, and the size increases continuously. The distance between quantum dots is decreasing, and even the island is connected. Secondly, the change of two-dimensional GE nanoisland with growth temperature and atomic deposition on the graphic substrate is studied. When the temperature is low, the deposited atoms are not affected by the graphic substrate. With the increase of temperature, the atoms nucleate into two-dimensional islands in the graphic substrate, but the diffusion ability of the deposited atoms is strong at too high temperature. It is not conducive to the formation of an ordered quantum dot array, but the small or too large amount of atomic deposition is not conducive to the preparation of the ordered quantum dot array, so that the quantum dot size is not uniform and the order is destroyed by the excessive assembly. Finally, the effects of growth standstill and deposited atomic energy on the surface morphology, island size distribution and spatial distribution of QDs on graphical substrates are studied. The study found that the longer the pause time is, the better the order and uniformity of the two-dimensional GE nanoscale island is: the increase in the number of pauses increases the diffusion ability of atoms. Therefore, when the number of pauses is moderate, an ordered and uniform two-dimensional GE nanoisland array can be obtained, and the optimal number of pauses is 3 times, and the increase of residual energy of the deposited atoms can make the distribution of two-dimensional GE nanowires on the graphic substrate more orderly. The size is also more uniform, which is due to the proper diffusion of the deposited atoms. By simulating the growth of two-dimensional GE nanowires on Si substrate, the physical mechanism of quantum dot growth is analyzed, and the technological parameters for the growth of high quality GE quantum dots are obtained. It provides an important theoretical basis for obtaining ordered quantum lattice, adjusting and optimizing the preparation process.
【学位授予单位】：云南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1;O614.431

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