Theoretical And Experimental Research OnⅢ-Ⅴ Semiconductor Nanowires And Related Axial Heterostructures

The research work in this dissertation is mainly supported by the grants from the National Basic Research Program of China, which our laboratory group undertakes in the Basic Research on Compatible Heterogeneous Integration and Functional Microstructure Assemblage for the Development of Novel Optoelectronic Devices (Grant No:2010CB327600)、the National Natural Science Foundation of China (Grant Nos:61020106007and61077049)、New Century Excellent Talents of China (Grant No:NCET-08-0736) and the111Program in University (Grant No:B07005).In recent years, semiconductor nanowires and the related heterostructures, due to the unique properties compared with macro-material, have aroused the great interest of the researchers. Based on semiconductor nanowire heterostructures, a new generation of electronic and optoelectronic devices, such as lasers, nano field-effect transistors, detectors and so on, have shown a broad application properspects. In this thesis, a great deal of work is demonstrated about the group III-V nanowires and the related heterostructures. Using the metal organic chemical vapor deposition technique, we have optimized the growth of self-catalyzed InP nanowires, analyzed the growth mechanism of the self-catalyzed InP nanowires, grown the GaAs/InAs axial heterostructured nanowires and systematically analyzed the morphology of GaAs/InxGa1-xAs/GaAs axial double heterostructure nanowires with different Indium content in the InxGa1-xAs segment. The specific research content and achievements are listed as follows:1、The morphology of self-catalyzed growth of InP nanowires on the InP(111)B substrate has been investigated at different temperatures,Ⅴ/Ⅲ ratiosand growth time. Under the optimized growth condition and regulating the growth time, we find that the growth of nanowires is mainly controlled by non-uniform adatom diffusion from the substrate and the sidewalls of the nanowire.2、The growth characteristics of GaAs/InA axial heterostructure nanowires has been analyzed. In the case of growing InAs segment onto the GaAs nanowires, due to the low Au-GaAs surface energy compared with Au-InAs, the catalyst alloy droplets move to the side of the nanowire. Based on the theory of thermal equilibrium, the unidirectional growth of GaAs/InAs axial heterojunction nanowire growth mechanism has been explained.3、Growth of GaAs/InxGa1-xAs/GaAs (0.2≤x≤1) axial double heterostructured nanowires at different In content in the InGaAs segment are demonstrated. The morphological, compositional and structural characteristics of GaAs/InxGa1-xAs/GaAs axial double heterostructured nanowires have been systematically investigated. It is found that the morphology of nanowires is closely related to the Au-In(Ga) composition in the catalyst, which also determines the incorpotion of indium in the InGaAs segment. A short period of pre-introduced Indium precursor in combination with the Gallium precursor interruption befor the formation of InGaAs segment, can help to obtain symmetric interfaces of GaAs/InxGa1-xAs/GaAs axial double heterostructures.4、In combination with the crystal nucleation thermodynamic theory, the influence of single-mode and multi-mode nucleation in the epitaxial process on the nanowite growth rate are summarized. Using the continuous medium elasticity model, analyses of the strain energy of the the nanowire axial and radial heterostructures are performed. For axial and radial heterostructured nanowires with cubic zinc blende structure, the relationship between the critical thickness of the epitaxial layer and the radius of nanowire is analysed with the application of the equilibrium state of minimum energy principle. In the case of radial heterostructures, for some core radius and a certain thickness of the shell, the dislocation density in the shell obtained from theoretical calculation are compared and analysed with the experimental data.