Metal-Induced Synthesis Of Ge Nanoclusters, Microstructures And Properties

Metal/semiconductor composite thin films have attracted much attention in the research field of information functional materials. In particular, these thin films have many potential applications in micro-electronic devices, optoelectronic components and solar cell etc. Thin film technology is a key technology for devices miniaturization, which also is an important method for preparing various novel functional thin films and devices. There are many ways about preparation of thin films, mainly including chemical vapor deposition (CVD) and physical vapor deposition (PVD), such as conventional physical vapor deposition technology: vacuum thermal evaporation, molecular beam epitaxy growth, magnetron sputtering method, and pulsed laser deposition, etc. With the rapid development of nanomaterials, the crystallization behavior and nanostructure characteristic of amorphous semiconductor Ge clusters induced by metal play an extremely important role in the application of micro-electronic devices and optoelectronic components.In this thesis, different thickness bilayer films are prepared via a simple way of vacuum thermal evaporation techniques. Ge nanostructures with the characteristic of different morphology are formed at thermal treatment under vacuum or N2atmosphere. These nanostructures features include nanoparticles, nanorings, and naofractals. Raman, XRD, SEM, TEM, AFM and HRTEM techniques are used to analyze the microstructure of the Ge clusters. The microstructure and electrical properties of thin films.also are investigated in detail.In Au/Ge bilayer films, the experimental results indicated that the fractal crystallization behavior and film resistance are influenced significantly by annealing temperatures and fractal dimensions. Measurements of film resistance provided the evidence that there exists a relationship between the film resistance and fractal dimension. We unexpectedly found that an Au/Ge bilayer film with an interesting nanofractal shows a nonlinear voltage-current behavior. Additionally, the microstructure of Au film plays an important role in the characteristics of Au/Ge bilayer films after annealing. The appearance of fractal architectures has significantly influence on the thermoelectric power (TEP) but little effect on the resistivity of the annealed bilayer film. In Pd/Ge bilayer films, the experimental results indicated that the fractal Ge nanoclusters with various sizes, densities, and fractal dimensions are affected by different annealing temperatures. The fractal dimension and film resistance (R) decrease monotonically with increasing annealing temperature. In Al/Ge bilayer films, the Ge nanofractal structure is successfully prepared by vacuum thermal evaporation techniques under thermal annealing in N2atmosphere. Experimental results further confirmed that the crystallization of amorphous Ge (a-Ge) preferred occurs surrounding Al grains. The samples with different annealing temperatures exhibit different morphology and fractal dimension. The fractal pattern exhibits perfect branched architectures and open structure when the bilayer films were annealed at400°C. These findings revealed new opportunities for future study of fractal Ge nanocluster and may be a promising material to constitute important building blocks for micro/nano-devices for microelectronic applications. It is also expected that these nanostructures offer exciting opportunities for both fundamental research and technological applications.