InGaAs Quantum Dot Growth Uniformity Controllability Study

In this paper, we have prepared In(Ga)As quantum dots by molecular beam epitaxy, reflection high-energy electron diffraction was used as real-time monitoring tool. A certain amount of Ga elements was deposited on GaAs(001) substrate to form Ga droplets, then the As valve was open to crystallize these droplets, we studied the influence of deposited Ga amount, the substrate temperature and As beam equivalent pressure to the formed GaAs nanostructures. Nanoholes were fabricated on GaAs(001) surface by Ga droplet etching,the evolution of In(Ga)As quantum dot formation was studied on this surface with varying In As supply,scanning tunneling microscopy was utilized for analysis the formation and distribution of quantum dots with increasing InAs supply. By growing multi-cycle In(Ga)As/GaAs structure, we studied changes in the density, size and spatial distribution of the quantum dots when increase number of the growth cycle.The results showed that a certain amount Ga elements were deposited on GaAs(001) substrate, when the amount of Ga exceeds a certain threshold(between 0.7 ~ 1.3ML), the Ga droplet structure will appear on GaAs(001) surface; then these Ga droplets were crystallized under As4 pressure, due to the variation of deposited Ga amount, the substrate temperature and As beam equivalent pressure, we can obtain GaAs nanostructures with single ring, double ring and ring-disk. Furthermore, in all of those factors, the effect of As beam equivalent pressure is most obvious. Nanoholes were fabricated on GaAs(001) surface by Ga droplet etching,then InAs quantum dots with varying InAs supply were formation on this surface by molecular beam epitaxy. The result indicated that In As will follow the Stranski-Krastanov growth mode on the GaAs flat surface. At the same time, on the nanohole location, the steps in and around nanoholes will restrict the nucleation of quantum dots. However, this restriction will become weaker with increasing InAs supply. Especially, when InAs deposition increased to 2 monolayers, ring-like nanostructures consist of In As quantum dots with uniform size will be observed on the nanohole location. Growing multi-cycle In(Ga)As/GaAs structure, the stress exist between InAs and GaAs will transfer along the vertical direction; with the increase in the number of growing cycles, In(Ga)As quantum dot density was decrease while their size were gradually increasing, at the same time, in the space of the entire substrate surface the quantum dots distribution, shape and their size were also becoming more and more uniform.