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采用离子束溅射沉积的方法在Si衬底上生长Ge量子点,观察到量子点的生长随Ge原子层沉积厚度θ的增加经历了两个不同的阶段.当θ在6—10.5个单原子层(ML)范围内时,量子点的平均底宽和平均高度随θ增加同时增大,生长得到高宽比较小的圆顶形Ge量子点,伴随着量子点的生长,二维浸润层的厚度同时增大,量子点的分布密度缓慢增加;当θ在11.5一17 ML范围内时,获得高宽比较大的圆顶形Ge量子点,量子点以纵向生长为主导,二维浸润层的离解促进量子点的成核和长大,量子点的分布密度随θ的增加快速增大;量子点在θ由10.5 ML增加到11.5 ML时由一个生长阶段转变到另一个生长阶段,其分布密度同时发生6.4倍的增加.离子束溅射沉积Ge量子点的生长演变与在热平衡状态下生长的量子点不同,在量子点的不同生长阶段,其表面形貌和分布密度的变化特点是在热力学条件限制下表面原子动态演变的结果,θ的变化是引起系统自由能改变的主要因素.携带一定动能的溅射原子对生长表面的轰击促进表面原子的扩散迁移,同时压制量子点的成核,在浸润层中形成超应变状态,因而,改变体系的能量和表面原子的动力学行为,对量子点的生长起重要作用.
The growth of Ge quantum dots on Si substrate by ion beam sputtering deposition shows that the growth of QDs goes through two distinct phases as the thickness of Ge atomic layer increases by 0. When θ is in the range of 6-10.5 single atoms (ML), the average bottom width and the average height of the quantum dots increase with the increase of θ at the same time, resulting in a domed Ge quantum dot with a smaller aspect ratio. With the growth of quantum dots, The thickness increases at the same time, and the distribution density of quantum dots increases slowly. When the θ is in the range of 11.5-17 ML, the domed Ge quantum dots with large aspect ratio are obtained. The quantum dots are dominated by the longitudinal growth and the two-dimensional wetting layer The dissociation promotes the nucleation and growth of quantum dots, and the distribution density of quantum dots rapidly increases with the increase of θ. The quantum dots transition from one growth phase to another when θ increases from 10.5 ML to 11.5 ML, and its distribution density With the increase of 6.4 times at the same time.The growth and evolution of Ge quantum dots deposited by ion beam sputtering is different from the growth of quantum dots in the state of thermal equilibrium.The change of surface morphology and distribution density at different growth stages of quantum dots is characterized by thermodynamics Under the conditions of the original surface As a result of sub-dynamic evolution, the change of θ is the main factor that causes the change of free energy of the system.The bombardment of the growth surface by sputtering atoms carrying a certain kinetic energy promotes the diffusion and migration of surface atoms and simultaneously suppresses the nucleation of quantum dots. In the wetting layer Forming super-strain state, therefore, to change the system energy and surface atomic dynamics, the growth of quantum dots play an important role.