Preparation, Vibrating And Luminescence Properties Of Ge-based CdSe Heterostructure Nanowires

The properties of Ge-based heterostructures are definitely dependent on their size, morphology and structure. Investigations on the inner relationships among these characteristics have become a focus in modern nanomaterials. These heterostructural nanomaterials are important for the applications prospect in modern optics, optoelectronics and integrated circuits. In this dissertation, the controllable synthesis, growth mechanism vibrational and luminescence properties of two kinds of Ge based CdSe heterostructures nanowires are mainly explored.1. Synthesis of two different kinds of CdSe-Ge heterostructure nanowires. Two kinds of different structural nanowires are fabricated by the chemical vapor deposition method based on the vapor-liquid-solid growth mechanism at different deposition regions using CdSe and Ge power as the raw materials. The first one is CdSe-Ge biaxial heterostructure, and the second is the Ge nanowire modified with CdSe particles on the surface. The co-growth possible growth mechanism is proposed on the basis of experiments and theoretical simulations. With the increasing of temperature, Ge nanowires is firstly evaporated and grown preferentially, because the sublimation temperature of Ge is lower than that of CdSe. Then, CdSe epitaxial layer homogeneously grown on the Ge (111) crystal plane, and forming CdSe/Ge heterostructure nanowire. The Ge nanowires wrapped by CdSe particles will be obtained in the lower temperature region when the CdSe is excess.2. Vibrational property of single heterostructure nanowires. The two kinds of Ge-based heterostructure nanowires are separately in ethanol and spin-coated on the graphite/Au substrate. Raman spectra of the two kinds of single nanowire are investigated at room temperature. The vibrational mode of Ge nanowire in CdSe/Ge biaxial heterostructure nanowires has a5cm-1red-shift in comparison with that of pure Ge nanowires. The vibrational mode of CdSe in CdSe/Ge biaxial heterostructure nanowires has a red-shift, but the relative intensity of the LO mode has a sharp decrease in comparison with that of CdSe nanoribbon. The shift of vibrational modes in CdSe/Ge biaxial heterostructure nanowires are all attributed to lattice mismatch at the interface of heterostructure. As for Ge nanowires surrounded by CdSe nanoparticles, the transverse optical (TO) mode of CdSe shifts from174.5cm-1to162cm-1, and the vibrational mode of Ge is not observed. However, a new wide peak located at272cm-1was detected in the Raman spectrum of single Ge nanowire surrounded CdSe nanoparticles. The new peak perhaps caused by the relatively low dielectric constant CdSe surface layer which leads to the Coulomb force among the atoms increasing and the vibration frequency of lattice decreasing.Luminescence property of the two kinds of the nanowire heterostructures. From the room-temperature PL spectrum, the emission peak and emission density of CdSe in CdSe/Ge biaxial heterostructure nanowires has a red-shift and the decreases compared with that of CdSe nanoribbon. Due to the large number of dangling bonds and the lattice mismatch of the heterostructure interface. The emission peak of CdSe in Ge nanowires surrounded by CdSe nanoparticles has a15meV blue-shift in comparison with that of CdSe nanoribbon, which may be attributed to the nannosized effect and morphology difference.3. Si micro-array is prepared by lithography and wet etching technology on Si wafer. The arcuate sidewall etching profile is formed due to anisotropy of Si (111) plane during the process of wet etching. A more vertical sidewall profile is achieved by changing experimental conditions. The preliminary results may lay the foundation for fabrication of Ge-based heterojuntion nanowire devices.