The successful integration of graphene into microelectronic devices is strongly dependent on the availability of direct deposition processes, which can provide uniform, large area and high quality graphene on nonmetallic substrates. As of today the dominant technology is based on Si and obtaining graphene with Si is treated as the most advantageous solution. However, the formation of carbide during the growth process makes manufacturing graphene on Si wafers extremely challenging. To overcome these difficulties and reach the set goals, we proposed growth of high quality graphene layers by the CVD method on Ge(100)/Si(100) wafers. In addition, a stochastic model was applied in order to describe the graphene growth process on the Ge(100)/Si(100) substrate and to determine the direction of further processes. As a result, high quality graphene was grown, which was proved by Raman spectroscopy results, showing uniform monolayer films with FWHM of the 2D band of 32 cm−1.
In a photoluminescence and surface photovoltage study of porous silicon films with crystallite dimensions assessed with the Atomic Force Microscope, we have found cases when the blue shifts of the luminescence spectrum and the optical absorption edge take place upon increasing crystallite dimensions, which is contrary to quantum size effects. Fourier transform infrared spectroscopy analysis of these samples shows significant differences in hydrogen and oxygen bonding, which imply that the origin of the luminescence is of chemical nature. Our results show that porous silicon luminescence is not a consequence of one mechanism, but rather results from several mechanisms with contributions depending on the chemistry and structure of porous silicon.
The dynamic response of an electron Fermi sea to the presence of optically generated holes gives rise to an enhanced interaction of correlated electron-hole pairs near the Fermi level, resulting in an enhanced oscillator strength for optical transitions, referred to as the Fermi-edge singularity. We studied this effect in modulation-doped quantum wells which provide confined dense Fermi sea, spatially separated from dopant atoms, easily accessible for investigations under low excitation conditions. The Fermi-edge singularity was observed in both photoluminescence and photoluminescence excitation experiments, although in the case of photoluminescence the samples had to be either co-doped with acceptors in the wells to provide necessary localization of holes or designed to allow for nearly resonant scattering between the electronic states near the Fermi energy and the next unoccupied subband of the 2D electron gas. The one-component plasmas, i.e., plasmas consisting predominantly of electrons or holes provide an easy way to study many-body interactions in semiconductors. Such situations are achieved by heavy doping of semiconductor materials beyond the metallic limit. Optical studies of the many-body phenomena involve the generation of additional electron-hole pairs, usually in concentrations much smaller than that of electron or hole plasma. For, let us say, n-type material the number of electrons remains practically unchanged in such situation, whereas the number of holes is determined by optical excitation. The holes then display some correlation effects, while the exchange effects are negligible unless very high excitation intensities are reached. Additional large contributions to the screening and renormalization effects arise from the interaction of the free carriers and the ionized impurities. A clear cut situation arises when the free carriers are spatially (751)
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