Study On Electrical Properties Of Ge Nano-Films And Thermoelectric Properties Of Si Nano-Materials

Low dimensional semiconductor nanoscale materials have attracted great attentionbecause of their special physical properties in electric and thermoelectric conversion. Ge has ahigher intrinsic holes mobility and superior quantum confinement effect than Si, therefore, Genano film material has excellent physical properties. In order to further understand electricaltransport properties, the Ge nano film has been prepared by ion beam sputtering method. Andthe thickness, phase structure, surface structure and electrical properties of the Ge nano-filmhave been investigated. The nano-pore Si has a stronger phonon scattering than bulk Si. Inorder to improve the ZT value of Si, nano porous Si has been prepared by electrochemicaletch method. As the template to prepare Si-base two-dimensional phononic crystal （TDPC）,the SiO₂microspheres were also explored. The details are as follows:1. The Effects of annealing temperature on the properties of Ge nano film have beeninvestigated. The film began to crystallization after annealed at500℃. The conductivity ofthe films changes with annealing temperature. All samples fit Mott’s Short-range hoppingconductive mechanism in high temperature region. And Greaves VRH theory is used toexplain the conduction mechanism in50-5K.2. The Effects of growth temperature on the properties of Ge nano film have beeninvestigated. When the growth temperature is higher than400℃, the Ge nano-film began tocrystallization. The roughness of the Ge nano-film increases slowly with the rise oftemperature, and the roughness increases sharply after the crystallization temperature. Allsamples fit Mott’s Short-range hopping conductive mechanism in high temperature region.And Mott’s VRH theory is used to explain the conduction mechanism in low temperature.3. The porous silicon was prepared by electrochemical etch method with doubleelectrobaths and it thermoelectric properties were studied. The porous silicon etched20minhas a higher ZT value than bulk Si due to the increase of its Seebeck coefficient and thedecrease of its thermal conductivity. The lower thermal conductivity is owing to phononscattering in the porous silicon. And phonon scattering happened in the porous silicon whosehole diameter being10³0nm is larger than that of the sample with large size hole. 4. As the template to prepare Si-base TDPC, the SiO₂microspheres have beensynthesised. The synthesis conditions of the SiO₂microspheres are as follow: Reactiontemperature is35℃. The volume ratio of TEOS and NH4OH is1:1and the reaction time is30min. The conditions and mechanism of different method to perpare self-assembly SiO₂microspheres template was deeply studied. The results show that the concentration of the SiO₂microspheres for preparing single layer template is1.9g/m by vertical deposition method.