FABRICATION AND OPTICAL PROPERTIES OF (I) ERBIUM-DOPED NANOWIRES CONTAINING GERMANIUM AND/OR ZINC OXIDE AND (II) POROUS GERMANIUM NANOWIRES

• Main Author: Huang, Xuezhen
• Other Authors: Jeffery L Coffer
• Format: Others
• Language: en
• Published: Texas Christian University 2010
• Subjects: College of Science and Engineering
• Online Access: http://etd.tcu.edu/etdfiles/available/etd-04282010-134727/

Nanomaterials have attracted great attention in the past two decades due to their superior mechanical, thermal, chemical, electrical and optical properties entirely different from bulk materials, which lead to numerous potential applications in nanodevices and nanoelectronics, such as FETs, LEDs, single electron memory devices, spin polarized electronics, quantum computing, sensors, photonic crystals/devices, solar cells etc. Based on the previous work on Er-doped GeNWs, a core-shell nanostructure was built by introducing Zn/ZnO shell onto Er-doped GeNWs. It was found that Zn sources and corresponding surface modification processes (CVD and PVD) have important impact on Er<super>3+</super> PL and ZnO UV/visible PL due to Zn₂GeO₄ formation, which were confirmed by HRTEM and XRD measurements. In another work, Ge and Er were used to modify the surface of ZnO tetrapods. Both strong ZnO visible PL and Er<super>3+</super> PL were observed; considerable enhancement of Er<super>3+</super> PL was made possible by Ge deposition as a sensitizer layer. The Zn₂GeO₄ phase observed could either separate from the ZnO phase or mix uniformly with the ZnO phase. As a control system, Er/GeO_x/ZnO nanofibers were fabricated by electrospinning of selected sol-gel precursor solutions. These types of nanofibers exhibited strong Er<super>3+</super> near IR PL at 1.54 &mum after annealing to remove the polymer template. XRD spectra indicate that the Er/Ge/Zn mixture likely forms a disordered phase, especially with high Er<super>3+</super> concentrations, which contributes to the strong Er<super>3+</super> PL with the reduction of Er-Er interactions. In another work, the fabrication of F-doped ZnO nanowires was investigated on different substrates with or without carrier gas (Ar). ZnO UV/visible PL spectra indicate that F-doping diminished the intensity of defect light emission at ~2.4 eV. Furthermore, ZnO/F-doped ZnO coreshell NWs were fabricated either by PVD or CVD processes; the PVD method provides better crystalline shell structures after annealing. The last work describes the fabrication of porous Ge nanowires by the anodization of Ge nanowires (grown on Si substrates) using ethanolic HCl as an electrolyte. An initial cathodic Cu electrodeposition step is found to provide useful kinetic control of the pore morphology and to stabilize the nanowires attached to the Si surface. A systematic evaluation of the role of electrolyte composition, current/voltage density, and its duration on the resultant Ge NW morphology and structure have been carried out. Preliminary photoluminescence (PL) measurements suggest strong emission in the visible region. The electrochemical anodization mechanism is discussed involving the periodic localization of pores and a varying potential distribution of free electrons along 1D GeNWs.