Research On Band Regulation And Optical Properties In GaAs-based Quantum Well Nanostructures

GaAs is a typical Ⅲ-Ⅴ group semiconductor materials,which is widely used in various light-emitting devices and high-frequency devices due to its direct band gap（1.42 e V@300K）and excellent electron mobility(～8500 cm² V^-1s^-1).In particular,GaAs-based nanostructures have shown great application prospect in micro-nano devices.But there are still some problems in GaAs-based nanostructures need to be resolved.For example,the phase control problem in GaAs nanowires and the problem of surface state in GaAs-based materials which is more obvious in nanowires with larger specific surface areas.Those problem severely limit the optical performance of GaAs-based nanowires.In addition,GaAs-based quantum well nanowire can be used as waveguide and gain material at the same time,which provides new idea for the development of micro-nano optoelectronic devices.In order to better excite the potential of quantum well nanowire devices,it is necessary to study the distribution of carriers and the energy band structure of quantum well.In addition,in order to meet the requirement of devices,modulating the emission wavelength is necessary.In the existing research,the emission wavelength is modulated by adjusting the thicknes of the quantum well and the length of the nanowires.However,this method has a small adjustable range and it is complicated for growth conditions.Proposing a more effective wavelength control method is an urgent request for micro-nano optoelectronic devices.In this paper,according to the growth principle of nanowire growth,we realized the phase control of GaAs-based nanowires by controlling the growth parameters and using a simple substrate processing technique.In order to solve the problem of the surface state of GaAs-based nanowires,wet passivation,plasma etching,and construction of core-shell structures are used to modify the surface of GaAs nanowires.The optical propertie of GaAs-based nanowires treated by different passivation methods were compared.Focusing on the energy band regulation and optical property of GaAs-based quantum well nanostructures,we have grown high-quality GaAs/GaAsSb/GaAs core-shell coaxial single quantum well nanowires.And by adjusting the alloy composition in GaAs-based quantum well nanowires,the band structure adjustment is realized.After that,the optical property of GaAs-based quantum well nanowires were studied through the characterization of photoluminescence spectroscopy,and the model of the carrier distribution and quantum well band structure in the quantum well nanostructures was constructed.The main research contents of this paper are as follows:（1）According to the vapor-liquid-solid growth mechanism of nanowires,we discussed the influence of growth parameters on the growth of GaAs-based nanowires.The crystal phase control in GaAs nanowires is realized by a simple substrate etching process.（2）The effects of wet passivation,plasma treatment,and construction of core-shell structure on the optical property of GaAs-based nanowires are compared and studied.The results show that the wet passivation method increases the emission intensity of GaAs-based nanowires by about 6 times.And the emission mechanism of GaAs-based nanowires will not change,but the stability is poor.Plasma treatment is incapable of improving the optical performance of GaAs-based nanowires and will introduce new defects.The Al GaAs shell constructed by in-situ growth can effectively improve the optical performance of GaAs-based nanowires（the emission intensity is increased by about 64 times）and has good stability.（3）The high-quality GaAs/GaAsSb/GaAs core-shell structure coaxial single quantum well nanowires are prepared by molecular beam epitaxy equipment.The energy band structure in GaAs/GaAsSb/GaAs quantum well nanowires is studied,and the power-dependent and temperature-dependent photoluminescence spectra are used to characterize the optical property of the grown nanowires,and the energy band structure and carrier distribution are discussed.The research results show that the GaAs/GaAsSb quantum well presents a quasi-type-II energy band structure under low Sb composition.In this structure,the energy gap between the conduction bands is small,and the carriers cannot be effectively confined to the quantum well.The electrons in the well can overcome the potential barrier after they have gained enough energy.（4）The GaAs/GaAsSb/GaAs core-shell structure coaxial single quantum well nanowires with different Sb composition are designed and prepared,and the band control in GaAs-based quantum well nanowires is realized by adjusting the Sb composition.Through the method of photoluminescence spectroscopy,we have studied the optical propery of quantum well nanowires with different Sb components.The results show that the GaAs/GaAsSb/GaAs coaxial single quantum well nanowires with 8%and 12%Sb composition both have a quasi-type-II band structure,and the quantum well nanowires with higher Sb composition show deeper quantum well depth and stronger temperature stability.