Growth Of In As Quantum Rings On GaAs Surface

In this thesis,droplet epitaxy method is applied to prepare InAs quantum rings structures on Ga As(001)substrate.The effects of deposition rate,deposition amount and arsenic flux on the growth process of indium droplets on Ga As surface were investigated by using the control variable method.By adjusting the substrate temperature,the growth mechanism of InAs nanostructure from droplet to quantum ring was explored.The conclusions drawn in this thesis are as follows:(1)Study on the effects of growth of InAs nanostructures on Ga As surface by changing the deposition rates with other conditions keep constant.It is found that the deposition rate affects the droplet density by changing the nucleation rate of In droplets.In other words,the nucleation rate of atoms on the substrate surface increases with the increase of deposition rate,which increases the density of InAs nanostructures on the Ga As surface.The phenomenon accords with the classical nucleation theory and the change of Gibbs free energy during nucleation.(2)Study on the effects of growth of InAs nanostructures on Ga As surface by changing the deposition amount with other conditions keep constant.It is found that with the increase of deposition amount,the volume of InAs nanostructures increases obviously,while the density climb up and then decline.And the typical anisotropic diffusion of atoms on the surface is founded.It shows that the change of deposition mainly affects the process of droplet ripening.More deposition amount provides more active in atoms to participate in the growth of in droplets.It promotes the process of droplet ripening,more atoms participate in the diffusion and collapse of droplets.Therefore,the morphology of InAs nanostructures appears the phenomenon of multiple quantum dots in the disk.(3)Study on the effects of growth of InAs nanostructures on Ga As surface by changing the arsenic flux with other conditions keep constant.It is found that with the increase of arsenic flux,the height of InAs nanostructures decreases and the diameter increases.In order to combine with arsenic atoms,Indium atoms in the droplets tend to diffuse outward to form two-dimensional nanostructures.InAs nanostructures exhibit a mixed structure of quantum dots and disk due to the average surface activation energy of atoms.The results show that Arsenic atom as the thermal activation energy provider,which changes the morphology of In droplet in the crystallization stage.(4)We choose the most suitable growth parameters(deposition rate: 0.15ML/s,deposition amount: 5ML,arsenic flux: 3.75 μTorr)to study the effect of different substrate temperature on the growth process of InAs quantum rings.It is found that the substrate temperature mainly changes the nucleation rate of indium atoms in the nucleation stage,the ripening rate of In droplet in the ripening stage and the reaction rate with arsenic atoms in the crystallization stage by increasing or decreasing the energy of In atoms.Based on the experimental results of increasing and decreasing the substrate temperature in the crystallization stage.It is verified that with the collapse and splitting of the droplet,Indium atoms in the droplet diffuse around the droplet and combine with As atoms to form InAs quantum rings on the Ga As surface.In this thesis,InAs quantum rings have been successfully fabricated on Ga As(001)surface by droplet epitaxy.We summarize the growth mechanism of InAs quantum rings based on the experimental phenomena.This work provides an experimental basis for the fabrication of InAs quantum rings by droplet epitaxy.