Anisotropic Properties Of Spatially Ordered InGaAs Quantum Dot-Chain Nanomaterials

Since quantum dot chain materials have the characteristics of confining electrons in a one-dimensional space and the characteristics similar to quantum wires,which makes quantum dot chains have many advantages over other materials.The work of this thesis is to study the anisotropy of InGaAs quantum dot chain material in terms of morphology,photoelectric properties,luminescence characteristics and stress.We mainly study the effects of different growth parameters on the growth process and anisotropy of quantum dot chains through systematic research and experimental methods.The following are the main research contents and research results:The anisotropy of the sample in terms of morphology was understood through AFM.As the growth temperature continued to increase,the morphology of the sample changed from a uniformly distributed isotropic feature to a chain-shaped anisotropic feature.After the temperature rises,the anisotropy is weakened again.Raman spectroscopy analysis shows that with the increase of growth temperature,TO and LO of InGaAs quantum dots show different degrees of redshift,which is attributed to the thermal expansion of the crystal leading to changes in the interatomic distance during the growth temperature.It also increases the diffusion rate of atoms during the growth process,reduces the phonon frequency,causes the Raman peak position to move to a low wave number,and causes the Raman peak to broaden.PL analysis shows that with the increase of the sample growth temperature,the lateral carrier coupling in the sample first increases and then weakens.This is the effect of the growth temperature on the anisotropy of the photoelectric properties in the sample.The calculation of the activation energy can analyze the frequency shift of the sample spectrum and the change of the full width at half maximum.By fitting the decay life of the sample,we can understand the anisotropic characteristics of the sample on the mechanism of luminescence.According to the results of the polarization fluorescence spectrum,withthe increase of the growth temperature,the fluorescence polarization degree of the sample will increase first and then decrease.The anisotropy characteristics of vertically stacked quantum dot chain materials with different In compositions were studied.Increasing the content of indium tends to separate the generated dots,which affects the lateral ordering of the stacked dot layers,and their anisotropy will also increase.At the same time,the higher indium composition will also enhance the stress anisotropy of the InGaAs layer,making the formation of quantum dots faster in specific directions.Spectral analysis shows that as the In content increases,the coupling between the quantum dots becomes stronger.Through variable temperature PL and TRPL tests,it can be concluded that samples with higher In content have lower thermal activation energy,which reflects the anisotropy of the photoelectric properties inside the quantum dot chain,that is,the potential barrier for carrier transport within the chain is relatively Low,the carrier transport has the characteristics of transmission anisotropy,which is also reflected in the process of carrier rearrangement and the effect on the luminescence life of the sample.