Surface Diffusion Of Group III Metal Atoms On GaAs (001) Substrates And Its Nanostructure Formation Mechanism

?-? semiconductor nanomaterials have been widely used in many fields,such as optoelectronics,microelectronics,and quantum communications.Based on the droplet epitaxy technique,many quantum structures(especially quantum dots or quantum rings)have been successfully fabricated with unique properties,providing their potential in new quantum devices in the future.However,the degree of control over nanostructure properties after self-assembly remains limited due to the inevitable stochastic processes during growth,while ideal devices require the ability to control nanostructure properties after growth.Thus,numerous research groups fabricated different ?-? quantum dots(or quantum rings)by droplet epitaxy.Unfortunately,most of those research are focused on the deposition of single-element droplets,and the mechanisms of diffusion and etching based on single-element droplets and multi-element droplets of group ? are still largely not systematically studied.In addition,the growth of ?-? nanostructures by droplet epitaxy based on patterned substrates was rarely reported.Therefore,the comprehensive use of droplet epitaxy to produce high-quality quantum structures is important to improve the performance of next-generation optoelectronic devices.This thesis systematically explored the formation of elemental nanostructures of ? material systems on flat Ga As surfaces to study the basic diffusion mechanism of group ? elements on Ga As surfaces.This thesis mainly focuses onto the following four apsects.1.The diffusion mechanism of gallium adtoms on flat Ga As substrates and the formation mechanism of concentric quantum rings are systematically investigated.Due to the diffusion limitation caused by the binding of Ga-As,Ga As concentric quantum rings were grown by temperature reduction crystallization.On this basis,multilayer Ga As concentric quantum rings were successfully grown by multi-step crystallization with the help of arsenic pressure controlling the surface diffusion of Ga atoms.Based on the existing diffusion model,we propose a gallium droplet surface diffusion model that combines gallium atom diffusion anisotropy and arsenic atom"trapping"of diffusing Ga atoms.This model is further used to explain the formation mechanism of Ga As concentric quantum rings,and calculate the diffusion activation energy of gallium atoms on the surface of Ga As(001)to be 0.7±0.1 e ?.The study of the diffusion mechanism of gallium atoms and the growth model of Ga As CNRs will provide an effective control means for the design and preparation of Ga As-CNRs.2.The diffusion mechanism of indium adtoms on flat Ga As substrates and the formation mechanism of quantum rings are studied.The droplet nucleation and various diffusion modes of indium atoms on Ga As surfaces are discussed in depth.The nucleation mechanism of indium droplets in Ga As is discussed under As-free pressure,and it is found that the indium atoms deposited on the surface are divided into two diffusion behaviors of outward diffusion and intermixing with the substrate.Using the diffusion limitation caused by the binding of In-As,the In As disk structure was grown by in situ crystallization annealing.The diffusion coefficient of indium atoms on the Ga As surface was calculated to be 1.2×10^-2 cm²/s and the diffusion activation energy E_In was0.62±0.05 e ?.Considering the effects of the substrate temperature and the magnitude of arsenic pressure on the diffusion of indium atoms,the In As quantum rings were grown by cooling crystallization.The diffusion anisotropy of indium atoms,the diffusion behavior of indium droplets on the surface of indium droplets by"trapping"of diffusing indium atoms by arsenic atoms and the intermixing of indium atoms and substrate atoms are used to explain the formation mechanism of In As quantum rings.3.The diffusion mechanism of aluminum elements on flat Ga As substrates and the formation mechanism of Al_xGa_1-x droplets is investigated.Based on the nucleation and diffusion of aluminum atoms in Ga As,the mechanism of preferential downward etching of aluminum atoms on the surface is found.A simplification model is proposed for calculating the alimunum atoms number for nucleation on the Ga As surface,and the nucleation mechanism of aluminum droplets on the surface is summarized.Based on this method,this thesis systematically investigates the effects of diffusion time,deposition rate,and substrate temperature on the nucleation of aluminum droplets and the surface diffusion of aluminum atoms.The nucleation energy of aluminum droplet is 1.61 e ? and the diffusion activation energy of aluminum on the Ga As(001)surface is 2.3 e ? obtained by calculations of classical nucleation theory.The effects of substrate temperature and deposition amount on the ripening and diffusion are discussed based on the ripening and surface diffusion model of alimunum atoms.The Al_xGa_1-x droplets were further investigated,and the experimental results showed that the surface after mixed deposition was divided into pure aluminum,pure gallium,and Al_xGa_1-x mixed droplets with three kinds of droplets existing simultaneously.Besides,the mechanism of In(Al)As quantum ring formation was elaborated.4.The effect of patterning substrates on the surface diffusion of indium atoms was investigated.A patterned Ga As(001)substrate with a 1.5?m trench and a 2?m terrace was made by wet etching,and the effect of the exposure process on the patterning of the Ga As(001)surface was discussed.It is found that indium atoms on the patterned Ga As surface preferentially nucleate on the terrace and climb from the trench to the terrace due to the presence of the Schwoebel-Erlisch barrier.With this mechanism,the effects of annealing time,substrate temperature on the nucleation and diffusion of indium atoms on the patterned surface are systematically investigated.A model is proposed to explain the diffusion pattern of indium atoms between terrace and trench on the graphical Ga As surface by counting the size and density of indium droplets and the morphological changes of indium droplets.An 8-cycle In_0.5Ga_0.5As QDs was grown by the S-K mode,demonstrating that the S-K mode results in differences in the content of surface In Ga As QDs due to the inconsistent concentration of indium and gallium atoms reaching the surface and the different arsenic distribution on the surface of substrate.It is found that although the stress transfer due to periodic growth has greatly weakened the effect of surface patterning on the selective growth of In_0.5Ga_0.5As QDs,however,the growth of In_0.5Ga_0.5As QDs at the plateau is still larger due to the E-S potential barrier at the slope and bonding bonds at the terrace.In summary,this thesis summarizes the different diffusion behaviors of group ? atoms on the Ga As(001)surface and prepares ?-? ring nanostructures by varying the substrate temperature and As pressure.The diffusion activation energy of group ? atoms on the Ga As surface is calculated and the physical mechanism of the formation of group ?-? nanostructures is investigated in depth.The potential limitations of the graphical Ga As(001)substrate on atomic diffusion are also proposed.On the one hand,the results of the study are important for a deep understanding of the intrinsic connection between the diffusion of group ? atoms on the Ga As(001)surface and the formation mechanism of nanostructures,and for a clearer understanding of the potential applications of the ?-? system;on the other hand,they provide the necessary theoretical guidance basis for experimental studies,and also for the study of On the other hand,it provides the necessary theoretical guidance for experimental studies,and also provides new preparation paths for the study of novel ?-? quantum devices.