Fabrication And Optical Properties Of Type-Ⅱ Heterogeneous Nanostructures Based Om ZnO

Low-dimensional nanomaterials have been attracted due to their unique physical and chemical properties and applications in optoelectronics, energy transfer, biology and medicine and optics. ZnO is an emerging semiconductor with a promising perspective in optoelectronic devices. On the basis of ZnO nanostructures, we studied the type-II heterogeneous nanostructures of ZnO-ZnSe and ZnO-Si, particularly suitable for light emitters due to the type-â…¡bandgap alignment. In this work, we studied the synthesis, growth mechanism and optical properties of some type-â…¡heterogeneous nanostructures.(1) ZnO nanowires and nanowire arrays have been synthsized via chemical vapor deposition with the help of ZnO seed layers fabricated by metal organic chemical vapor deposition and Au films deposited by sputtering. ZnO nanostructures are also synthesized by solution methods. In aqueous solution, the size of ZnO nanorods is dependent on the Sodium Citrate concentration. In organic solvent, the morphology of ZnO nanostructures is changed with different surfactants.(2) The high efficient orange emission in ZnO:Se nanorods is discussed with steady emission photoluminescence, excitation photoluminescence, time-resolved photo luminescence and temperature-dependent photoluminescence. Se impurities in ZnO play a critical role in the orange emission. A model is provided to explain the recombination process in ZnO:Se nanorods.(3) The microstructures of ZnO-ZnSe nanorings are studied to explain the growth mechanism. The highly bright orange emission is also observed in the ZnO-ZnSe nanorings.(4) Silicon nanowire arrays are fabricated via metal nanoparticles assisted electroless etching method. The shape of silver nanostructures determines the morphology of as-fabricated silicon nanowire arrays. The evolution of silver nanoparticles depends on the silver ion concentration and immersion periods in silver nitrate aqueous solution.(5) Porous silicon nanowire arrays are fabricated in higher hydrogen peroxide concentration and exhibit an emission band in the range of visible light. Hydrogen peroxide concentration is a key to the orange emission from silicon nanowires. The different resistance of silicon nanowires is responsible for deviation of photon energy in emission bands.(6) ZnO-Si core-shell nanowire arrays and ZnO nanodots decorated on silicon nanowire arrays are prepared by metal organic chemical vapor deposition. The pressure in reaction chamber and reaction periods are responsible for the different morphology of ZnO nanostructures. Furthermore, ZnO layers are coated onto the surface of porous silicon nanowire arrays. A emission band covering entire visible light range is observed in porous silicon-ZnO core-shell nanowire arrays. The type-II bandgap alignment is responsible for the simultaneous emission in silicon and ZnO.