Browsing by Subject "Hot carriers."
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Item Open Access Hot electron interactions in nanostructures(Bilkent University, 1997) Kaya, Ismet InonuModern semiconductor growth and processing techiques have provided the capability of fabricating a huge variety of devices which have atomically precise layered structures and lateral patterns with nanometer sizes. This not only provided novel device possibilités but also opened a new field in condensed matter physics, so called mesoscopics. It does not seem likely that the mesoscopic electronic devices will be available in the near future. Two main obstacles for mesoscopic electronics are the low temperature requirements and the breakdown of the phase coherence of the carriers as their energies exceed the Fermi level. This strongly suggests the investigation of the excited carriers with energies well in excess of their thermal equilibrium energy as the dimensions shrink. In this thesis, the interactions of hot electrons in semiconductor and metal structures with deep submicron characteristic dimensions have been studied. Tunneling Hot Electron Transfer Amplifier (THETA) constructed by abrupt semiconductur heterojunctions is a perfect system to analyze the interaction of hot electrons with cold electrons and the other possible excitations in solids. Recently, it has been discovered that an electron multiplication effect took place in such devices under certain conditions and resulted in a transfer ratio of greater than unity. In this work a novel fabrication technique has been developed. It would make it possible to utilize this effect for fabrication of a high frequency oscillator in the THz regime, in a future work. In addition, a kind of lateral THETA device has been constructed using a Two Dimensional Electron Gas structure. Electron multiplication effect for the first time has been observed in 2DEG structures. Moreover, the dependence of the effect on parameters such as injection energy, emitter and collector barrier heights and electron transit length has been investigated. The other direction of the work has been the investigation of metal wires under extremely high current densities. A strong nonlinearity in conductivity is introduced when a free standing submicrometer wire is biased to heat upto very high temperatures. The geometry of two crossing wires has been investigated under this condition.Item Open Access Probing hot-electron effects in plasmonic surfaces using X-ray photoelectron spectroscopy(Bilkent University, 2014) Çupallari, AndiHot-electron effects in plasmonic structures have been recently investigated as potential alternative mechanisms for solar energy harvesting and photodetection. [1][2][3] Hot-electron effects provide a semiconductor free route for the conversion of photons into electrical power. Here we investigate plasmonic hot electron effects in Metal-Insulator-Metal (MIM) structures using X-ray photoelectron spectroscopy (XPS). XPS has been previously used to investigate optoelectronic effects in semiconductors and nanocomposite surfaces. [4][5][6] Here, a similar approach is used to characterize the plasmonic and hot electron effects in MIM Junctions. Monochromatic Laser excitation with 450, 532 and 650 nm wavelengths are employed to illuminate the plasmonic surfaces fabricated using thermal evaporation, atomic layer deposition and electron beam lithography. The top metal of the MIM structures act as the plasmonic antenna (metal nanodiscs and gratings/stripes) that provide wavelength selective or wide band optical absorption. Plasmonic enhancement at the interface between the top metal and the insulator enhances the absorption of light in the device and leads to excitation of a larger number of hot electrons from the metal. Hot electron effects are characterized through studying the metal-insulator-metal junction and comparing shifts of binding energy belonging to the top metal islands for dark and illuminated conditions. XPS spectrum provides important information regarding the plasmonic and hot electron effects in the interface between top metal and the dielectric. A systematic study of the dependence of the XPS spectra on excitation wavelength, light intensity, polarization, insulator thickness and nanostructure geometry is presented. Effects of using different metals and insulator materials are also studied in symmetric and asymmetric tunnel junctions. Keywords: