CUHK electronic theses & dissertations collection

Finally in combination with c-AFM and EFM, the high-k materials breakdown behaviors are also interrogated. The breakdown processes are classified into three stages: pre-breakdown (pre-BD), soft breakdown (SBD) and hard breakdown (HBD). And a HfOx nano-pattern is fabricated with the aid of AFM. The dot growth characteristics on the pulse amplitude, duration and humidity are scrutinized.In this thesis, the single CdS nanobelt devices are fabricated successfully. The photosensitivity at 1V is up to 8 x 103 A/W and the electron mobility reaches to tens of cm/V·s. Based on these excellent optoelectronic properties, the CdS nanobelt becomes a good choice for interrogation on the charge transport characteristics on a nanometer scale. The transistor measurements show that the performance of CdS nanobelt device can be influenced by illuminations and ambient conditions, which result from the metal/CdS nanobelt contact and nanobelt surface redox reactions.The intrinsic carrier transport characteristics in CdS nanobelt can be investigated by reconstructing of the local surface band diagram with the aid of SSPM. A ∼0.50 eV upward band bending can be obtained in the dark. The surface depletion length induced by the negative surface oxygen adsorbates is estimated to ∼66nm if a concentration of 1017 cm -3 shallow donors is assumed in the CdS nanobelt. This depletion length is close to the height of the ultra-thin CdS nanobelt. These adsorbates result in the surface depletion region expansion and the conduction channel reduction, which is responsible for the CdS conductance drop. Above the band-gap illumination or to the oxygen-deficient environment can effectively reduce the surface band bending and the depletion region, finally increase the conduction channel, which is one of the main reasons for the large photosensitivity and highly oxygen sensitivity for the single CdS nanobelt device.To sustain Moore's law scaling trend beyond COMS, one-dimensional (1D) nanostructures, e.g. carbon nanotubes and semiconductor nanowires, are proposed to act as fundamental nanoscale blocks in the future electronic and optoelectronic devices. Therefore it is very crucial to understand the unique nature of electronic properties for 1D nanostructures in designing novel nanoelectronic devices and optimizing the device performance. In this thesis, the charge transport properties of nanostructure devices are studied. A method called photo-assisted scanning surface potential microscopy (SSPM) is developed, which yields a direct measurement of the electrostatic potential distributions across the 'biased' nanostructured device under different illumination conditions. Our efforts provide significant understanding of the nature of charge transport in nanoelectronics.We can simply fabricate the MSM device using single CdS nanobelt. A positive Schottky barrier is found at the electrode/CdS nanobelt junction because of the unequal work function or the Fermi level pinning by the surface states. The barrier height is estimated to be 0.38 eV by fitting the temperature dependent I-V curves. A big potential drop at the junction can be visualized by SSPM. The calculated contact resistance for the electron injection is much larger than that for the CdS nanobelt, which illustrates that the transport properties of CdS nanobelt device are dominated by the charge injection process. The change in contact resistance and nanobelt resistance under the above bandgap illumination are measured by photo-assisted SSPM. The experimental results show that in the dark, the charge transport for the CdS nanobelt device is dominated by electron injection, while under high light intensity, the charge transport is governed by the intrinsic nature of CdS nanobelt.With the aid of SPM, the charge injection and carrier transport characteristics of the individual CdS nanobelt device are systematically interrogated and comprehensively demonstrated, which are useful for designing and fabricating the nanostructured electronic and optoelectronic devices.An, Jin.Adviser: Jiambin Xu.Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3674.Thesis (Ph.D.)--Chinese University of Hong Kong, 2008.Includes bibliographical references.Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Abstracts in English and Chinese.School code: 1307