The Research On Ⅲ-Ⅴ Semiconductor Nanowire Heterostructures And Nanowire/Quantum-Dot Heterodimensional Complex Structures

Semiconductor nanowires have become a hot topic in information science and nanomaterials due to their unique structural characteristics and excellent electrical and optical performance. Particularly, Ⅲ-Ⅴ nanowires are promising in new-generation solid electronic and optoelectronic devices thanks to their outstanding advantages of direct bandgap, high electron mobility, as well as controllable growth. The present thesis focuses on nanowire heterostructures and nanowire/quantum-dot heterodimensional hybrid structures, which are considered as the key elements of Ⅲ-Ⅴ nanowire optoelectronic devices. The main contributions are as follows:1. Ⅲ-Ⅴ nanowire/quantum-dot radial heterodimensional complex structures(1) Stranski-Krastanov (S-K) InAs quantum dots are epitaxially grown on the sidewalls of Au-catalyzed GaAs nanowires by metal organic chemical vapor deposition (MOCVD) for the first time. The morphology, structure and distribution characteristics of quantum dots are systematically characterized. A formation mechanism of quantum dots based on substrate surface adatom diffusion is proposed. The dependence of distribution characteristics of quantum dots on the diameter of nanowires is discovered, and the evolution of quantum dots with deposition time is revealed. F-P resonant modes of quantum dots are observed at77K, suggesting a decoupling of gain medium and resonant cavity. Photoluminescence of the quantum dots is observed at room temperature for the first time. The effect of electron-phonon scattering and thermal penetration of carriers on the temperature-dependent optical properties of quantum dots is revealed.(2) S-K InxGa1-xAs quantum dots are epitaxially grown on the sidewalls of GaAs nanowires for the first time. The variation of emission wavelength of quantum dots with In content is observed. The physical mechanism that both the composition and size of quantum dots influence the optical properties of quantum dots and dominate alternatively is revealed. The phenomenon that the linewidth of quantum dots increases with decreasing the In content is observed and explained.(3) Multishell S-K InAs quantum dots are epitaxially grown on the sidewalls of GaAs nanowires for the first time by using GaAs spacing layers. Single-array distribution character of quantum dots on the main body of nanowires is observed and explained. A "double peak" phenomenon is observed in the emission of multishell quantum dots, and the incomplete electron coupling in multishell quantum dots is revealed.(4) The influence of nanowire density on the formation of quantum dots is revealed. GaAs/InAs nanowire/quantum-dot hybrid structure is fabricated on Si substrate by reducing the nanowire density through using Au aerosols as catalyst. The influence of substrate surface properties on the characteristics of quantum dots is studied.(5) InGaAs nanowires and InGaAs/InAs nanowire heterostructures are fabricated, and the factors that hinder the formation of S-K InAs quantum dots on InGaAs nanowires are analyzed. GaAs/InGaAs nanowire core-shell heterostructures are fabricated, and S-K InAs quantum dots are fabricated on the core-shell heterostructures subsequently. A nanowire-based "dot-in-well" structure is fabricated based on the structure aforementioned. The emission properties of the "dot-in-well" structure are characterized and the effect of InGaAs quantum well on the optical properties of quantum dots is revealed.(6) InAs quantum dots are grown on the sidewalls of InP nanowires with mainly zinc blende (ZB) structure. A formation mechanism of quantum dots based on selective aggregation of adatoms is proposed. GaAs/InP nanowire core-shell heterostructures are fabricated, and S-K InAs quantum dots are subsequently grown on the core-shell heterostructures for the first time. The formation mechanism of quantum dots is explained and the optical properties of quantum dots are characterized.2. Ⅲ-Ⅴ nanowire heterostructures and related photovoltaic devices(1) The GaAs/InGaAs nanowire core-multishell quantum well structure is fabricated, forming a resonant cavity separated from the gain medium. The photoluminescence of the quantum well is characterized and the effect of In content and well thickness on the optical properties of quantum well is studied. The F-P cavity resonant modes are observed, and the effect of excitation power, temperature, as well as the well thickness on the mode properties is studied systematically.(2) Straight and high-quality GaAs/InAs nanowire axial heterostructures are grown on Si substrate by using AlGaAs/GaAs buffer layers and InGaAs composition-graded section. The variation of crystal phase of InAs nanowire on its diameter and length of GaAs nanowire is discovered.(3) A novel solar cell structure based on tandem III-V nanowire core-shell pn junction arrays is proposed, which exhibits much higher performance compared with single core-shell pn junction solar cell as well as tandem axial pn junction solar cell according to simulated results.(4) A pn diode based on GaAs nanowire core-shell pn junction arrays is fabricated, which exhibits obvious rectification behavior.