Research On The Growth Process Of Single-layer Ordered InGaAs/GaAs Quantum Dots

InGaAs/GaAs quantum dots?QDs?have been widely used in QD infrared detectors,QD lasers,QD light-emitting diodes and other optoelectronic devices owing to their outstanding photoelectric properties.However,the performance and application range of these devices mainly depend on the size uniformity and ordering of QDs.With the development of preparation technology and characterization methods of nano-semiconductor materials,the ordered QDs can be fabricated on micro-machined graphical substrates by molecular beam epitaxy technique.However,due to the existence of defects and impurities inevitably introduced during fabricating patterned substrates,something disadvantageous would affect the growth of QDs and device properties.Therefore,in order to obtain the ideal available quantum dots and expand the application range of optoelectronic devices of QDs,it's crucial to realize the ordered distribution of QDs through study the process.In this paper,the growth process of ordered In_0.5Ga_0.5As/GaAs QDs has been studied based on flat and non-flat GaAs substrates by molecular beam epitaxy technique respectively.An atomic level flat GaAs surface is obtained through continuous growth of GaAs buffer layer and in-situ annealing,and is used for growing QDs.The influence of annealing time,growth rate and substrate temperature on the size distribution of In_0.5Ga_0.5As QDs are investigated.The result shows that the size uniformity of QDs is improved by introducing a certain time of annealing because of ripening.Meanwhile,the QDs with high density and small size can be prepared under the condition of low temperature and high growth rate,while QDs with low density and uniform size prepared via high temperature and low growth rate.Finally,the process of In_0.5Ga_0.5As QDs grown on a flat GaAs surface with relatively uniform size is obtained,and lays the foundation for the subsequent selection of growth parameters for the preparation of uniformly ordered quantum dots on non-flat GaAs substrates.The non-flat substrates surface mainly includes Ga droplet template with nano-holes and GaAs buffer layer with multi-steps.The GaAs buffer layer with nano-holes can be etched by the droplet of Ga at high temperature,while buffer layer with multi-steps can be fabricated by discontinuous growth.According to the growth process obtained from the flat substrate,the interaction between Ga droplet template and the growth temperature of QDs and deposition amount of atoms has been studied.The results show that the nano-hole modulates the density distribution of QDs.With the decrease of temperature,the phenomenon of nano-hole collapsing is gradually weakened,while the modulation of the size and density distribution of QDs enhanced,and the low-temperature growth is beneficial to the nucleation of QDs on the substrate of Ga droplet template.In addition,the QDs can nucleate only in the nano-hole region by reducing the deposition amount of atoms under the critical thickness.The growth parameters obtained from the flat substrate surface is used for growing In_0.5Ga_0.5As QDs on the surface of GaAs with different morphologies,and spatial distribution of In_0.5Ga_0.5As QDs is related to the shape and distribution of the steps.Chain-like QDs are apt to grow along the[?]direction while buffer layer contains numerous strip-like platforms,yet QDs would be disorder while platforms distributed randomly.At last,statistical analysis of size distribution of QDs has been done,and the result shows that,ordered chain-like In_0.5Ga_0.5As QDs could be prepared on a buffer layer contains numerous strip-like platforms.