A Study Of Growth Mechanism And Transport Properties For Diluted Magnetic Semiconductor Sn1-xMnxO2One-dimensional Nanostructures

Because of the discovery of spin-related phenomena and its important application prospect, tremendous efforts have been devoted to the research on spintronics around the world. Among various spintronics device systems, magnetic semiconductors are expected to be the dominant materials for next generation micro-electronic or nano-electronic devices with the electron spins. Until now most of efforts have been focused on the preparation and characterization of thin film and powder materials, a few work has been done on the one-dimensional diluted magnetic semiconductor (DMS) nanostructures. Semiconductor one-dimensional nanostructures are attractive components for nanometer scale electronic and photonic device applications. Recently, various of nano-devices including ultraviolet photodetectors, field-effect transistor, Schottky diodes and so on have been fabricated utilizing one-dimensional nanostructures.In this thesis, one-dimensional (ID) Sn1-xMnxO2nanostructures have been fabricated using catalyst assisted chemical vapor deposition (CVD), and the growth mechanism and transport properties of the nanostructures have been discussed in detail. The structure and morphology of the nanostructures were characterized by x-ray diffraction (XRD)、scanning electron microscope (SEM, Hitachi S-4800)、high resolution transmission electron microscope (HRTEM) and corresponding selected area electron diffraction (SAED). The chemical bonding states and the composition of the products were determined by x-ray photoelectron spectroscopy (XPS, VG Scientific ESCALAB-210spectrometer) and energy dispersive X-ray (EDS). Field-effect transistor (FET) based on an individual Sno.98Mn0.02O2nanowire was fabricated,and the electrical transport properties were measured. Magnetic properties were measured by superconductivity quantum interference device (SQUID) magnetometer.The main results as following:(1) SnO2and Sn1-xMnxO2one-dimensional nanostructures have been successfully synthesized by a chemical vapor deposition (CVD) with the direction randomly on the Si substrate. The nanostructures are smooth and homogeneous in diameter.(2) The increasing of catalyst gold layer is favor of the growth of SnO2nanowires, but not favor of the doping of Mn. The higher contents of Mn, the lower the quantity of products. The higher growth temperature, the smaller diameter nanowires will be generated. With the increasing of the flow rates of Ar, the quantity of nanowires increased and the diameter of nanowires became smaller and uniform. With the increasing of the flow rates of O2, the length of nanowires became shorter. The growth mechanisms of SnO2and Sn1-xMnxO2ID nanostructures are different, SnO21D nanostructures were dominated by Vapor-Liquid-Solid (VLS) progress, while Sn1-xMnxO2were dominated by Vapor-Solid (VS) progress. We discussed the VS growth mechanism in detail.(3) XRD and SAED revealed that the nanostructures are of tetragonal rutile single crystal SnO2structure.(4) XPS showed that Mn3+and Mn4+ion substitution for Sn4+in SnO2lattice and lots of oxygen vacancies are existed in nanowires. The main peak of PL was caused by Oxygen vacancies.(5) Sn0.98Mn0.02O2nanowires are n type semiconductor.The resistivity, conduction electron density, and the mobility of Sn0.98Mn0.02O2nanowire were estimated to be0.7Ω·cm,5.17×1018cm-3, and12.8cm2/Vs, respectively. From the dependence of electron concentration on temperature, we have determined the activation energy of Sn0.9sMn0.02O2nanowire to be133mEv. In addition, UV irradiation leads to an insulator-to-metal transition at170K.(6) The Sn0.9sMn0.02O2nanowires samples exhibit obvious hysteresis loop, indicating the ferromagnetic ordering exists in the materials at room temperature. The test results show the room temperature ferromagnetism (RTFM) is the intrinsic property of the nanowires. The origin of RTFM can be interpreted in terms of band coupling model.