Study On The Diffusion Behavior Of Ga Atoms On The Surface Of AlGaAs Thin Films

III-V nano-semiconductor materials can be used to fabricating devices which includes high electron mobility transistors,lasers and infrared detectors due to their unique properties,and thus being used widely in scientific research,medical and environmental protection and other fields.Mastering the motion law of III-V group atoms under different conditions is the key to obtaining the growth method of III-V materials with different characteristics.In this paper,the diffusion of Ga atoms on Al_0.4Ga_0.6 As/GaAs surface is explored by droplet epitaxy in a molecular beam epitaxy system,and a reflection high-energy electron diffraction is used to monitor the experimental process.Controlling variable method is adopted as an approach to study on the diffusion of Ga atoms on Al_0.4Ga_0.6 As/GaAs surface under different conditions by changing four parameters including annealing time,arsenic pressure,substrate temperature and deposition amount,and results are characterized and analyzed by scanning tunneling microscope and atomic force microscope.The main works of this paper are as follows:（1）The same amount of Ga is deposited at a certain temperature without As pressure.The Ga droplets become larger and larger while the density decreasesas the annealing time increases,and nanoholes gradually appear on the surface.The analysis of the experimental results shows that the droplet collapse caused by the combination of Ga atoms in the droplets and the As atoms on the surface leads to the formation of nanopores.However,accroding to the results,there is a critical point in the annealing time.When the critical point is not reached,the motion pattern of Ga atoms in the droplets is mainly either diffused outward or combined with the surface As atoms.After reaching the critical point,the motion pattern of Ga atoms in the droplets gradually changes from the outward diffusion mode to the longitudinal dissolution substrate mode.（2）When the As pressure is different,also the same amount of Ga deposited at the same temperature,the nano-holes and the nano-disks appear on the surface after the Ga droplet is crystallized,and the Ga atom still has the behavior of lateral diffusion and longitudinal diffusion,and the diffusion distance of Ga atoms decreases as the As pressure increases.Meanwhile,the Ga atoms mainly diffuse laterally under low As pressure,while longitudinal dissolution would happened under high As pressure.（3）The effect of temperature on Ga atoms is also significant.When the temperature increases,density of nano-holes decrease and depth increases,radius of the nano-disk also increases.Therefore,higher the temperature,stronger the lateral diffusion and longitudinal dissolution of Ga atoms.By calculation,the diffusion activation energy of Ga atoms on the Al_0.4Ga_0.6As/GaAs surface along the[1-10]direction and[110]direction is 0.84eV and 0.95 eV,respectively,showing anisotropy.（4）When the As pressure is the same and the deposition amount of Ga is different,the surface morphology is dominated by nano-holes and nano-disks at the same substrate temperature.As the amount of deposition increases,the anisotropy of the nano-holes become more and more obvious;The size of the nanodisk increases with the increase of the deposition amount,and tends to be gentle when it increases to a certain value,and changes from two-dimensional growth to three-dimensional growth.