The Growth Of Ge Nano-islands On Si(100) Substrate Simulated By Kinetic Monte Carlo

Semiconductor quantum dots (QDs) have a wide range of application prospects in nanoelectronics, nanophotonics and optoelectronics. Solid-state quantum devices depended on QDs will play an important role in quantum information technology. Because the Ge/Si QDs are compatible with large scale integrated circuit, their researches become one of the hot topic. To better understand the effects of growth factors and strain on the formation of QDs, kinetic Monte Carlo method has been widely used to study the growth of QDs. And the results are correct.In this dissertation, combined with MATLAB programming, kinetic Monte Carlo (KMC) method was used to simulate the early growth stages of Ge nano-islands on Si (100) substrates. The formation and evolution of two-dimensional Ge nano-islands in S-K mode was studied. However, the two-dimensional Ge nano-islands were too small to be studied in the experiment. Therefore, the KMC simulation was a powerful tool to solve this. The square grids of200×200were used as the Si (100) substrate for Ge nano-islands growth in this dissertation. The deposition and diffusion of adatoms were taken into account in these simulations without desorption process. The periodic boundary conditions were used to research adatoms diffusion in the substrate.Firstly, the effect of the growth parameters on the nucleation sites, size and uniformity, density, and distribution of two-dimensional Ge nano-islands were systematically studied. The results shown that with the increase of temperature, the diffusion ability of adatoms enhanced with temperature increase, which led to the island size increase and the density decrease. And the stability of two-dimensional Ge nano-islands was also studied during annealing. The average diffusion length of adatoms increased with annealing time. The adatoms were easy to diffuse to the place with lower potential energy. Then the island size increased and the density decreased. The Ostwald Ripening process could be observed. With the coverage of Ge increase, the density increased firstly and then reduced, which resulted in larger size and smaller distance between islands. Ultimately, these islands bonded together.Secondly, the impacts of growth temperature and Ge coverage on adatoms diffused on the patterned substrates were investigated. The islands were distributed randomly and the nucleation sites were not determined by patterned substrate at the low growth temperature. After temperature raised, the adatoms were inclined to nucleate in nanopore. But they ran out of nanopore at higher temperature due to the stronger diffusion ability, which was adverse to the growth of ordered islands array. Furthermore, the ordered islands array could be obtained at sutable Ge coverage. With low coverage, the island size was nonuniform. Inversely, the island could be formed outside nanopore and the array was destroyed.Finally, the island size and spatial distribution on patterned substrate was discussed at different growth interrupted conditions and deposited atom energy. Within the range of interrupted time, the islands were ordering and uniform at longer time. With number of interruption increasing, the atoms diffusion ability will be improved. The evolution of island under growth interruption was similar with those island at temperature increased. Therefore, the order and uniform QD array could be achieved when the interrupted number was appropriate. In our simulation conditions, the interrupted number was selected3times.In addition, the energy of deposited atoms was beneficial to the order and uniformity of islands array due to suitable adatom diffusion.In general, the physical mechanism and the effect of technology conditions of two-dimensional Ge nano-islands growth was simulated by KMC method, whose results would provide an important basis for controlled growth of Ge islands and ordered island array.