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n-channel and p-channel amorphous-silicon thin-film transistors (a-Si:H TFTs) with copper electrodes prepared by a novel plasma etching process have been fabricated and studied. Their characteristics are similar to those of TFTs with molybdenum electrodes. The reliability was examined by extended high-temperature annealing and gate-bias stress. High-performance CMOS-type a-Si:H TFTs can be fabricated with this plasma etching method. Electrical characteristics of a-Si:H TFTs after Co-60 irradiation and at different experimental stages have been measured. The gamma-ray irradiation damaged bulk films and interfaces and caused the shift of the transfer characteristics to the positive voltage direction. The field effect mobility, on/off current ratio, and interface state density of the TFTs were deteriorated by the irradiation process. Thermal annealing almost restored the original state's characteristics. Floating gate n-channel a-Si:H TFT nonvolatile memory device with a thin a- Si:H layer embedded in the SiNx gate dielectric layer has been prepared and studied. The hysteresis of the TFT's transfer characteristics has been used to demonstrate its memory function. A steady threshold voltage change between the "0" and "1" states and a large charge retention time of > 3600 s with the "write" and "erase" gap of 0.5 V have been detected. Charge storage is related to properties of the embedded a-Si:H layer and its interfaces in the gate dielectric structure. Discharge efficiencies with various methods, i.e., thermal annealing, negative gate bias, and light exposure, separately, were investigated. The charge storage and discharge efficiency decrease with the increase of the drain voltage under a dynamic operation condition. Optimum operating temperatures are low temperature for storage and higher temperature for discharge. a-Si:H metal insulator semiconductor (MIS) capacitor with a thin a-Si:H film embedded in the silicon nitride gate dielectric stack has been characterized for memory functions. The hysteresis of the capacitor's current-voltage and capacitance-voltage curves showed strong charge trapping and detrapping phenomena. The 9 nm embedded a-Si:H layer had a charge storage capacity six times that of the capacitor without the embedded layer. The nonvolatile memory device has potential for low temperature circuit applications.

The goal of this paper is to study the mechanism that may lead to the change of physic properties by annealed amorphous AZO samples, that were grown by RF magnetron sputtering, by an excimer laser or a tube furnace or both. By using of the Taguchi Methods, which is in expected to be a fast and efficiency method, to search the best process parameters and to understand what mechanism stood behind the change of these parameters. We found that polycrystalline AZO films may be formed very easily when were grown at a temperature higher than 150K. Amorphous AZO films may grow successfully only at low growth temperature, ~77K. Annealing in tube furnace can alter the crystalline properties. Recrystalization starts at 325oC. Laser annealing will also recrystalize the amorphous AZO films with laser energy density higher than 160mj/cm2. Unfortunately, neither method provide enough improvement in the electric conductivity.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI Company.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

No description available.

No description available.

This thesis analyses the effect of varying the compositions of co-evaporated V205/TeO2, W03/CeO2, SiO/TeO2 and W03/TeO2 amorphous thin films on their electrical and optical properties. Some information about the electronic properties of these oxides may be obtained by comparison of the results. In the oxide systems containing transition metal ions the expression for hopping energy at low temperatures contains a term due to the hopping energy of polarons in addition to that due to the disorder. In the dielectric SiO/TeO2 thin films the distortion of 'the molecule is thought to be quite weak and thus the carriers do not form polarons. They would move by hopping at the band edge at low temperatures and by excitation to a mobility edge at high temperatures. The electrical conductivity of V205/TeO2 amorphous thin films is discussed in the light of the Mott(1968) theory. The optical absorption edge was found to obey the direct forbidden transitions equation cc ico=B(fiw-EOP)3'2. The frequency-squared dependence of the conductivity of W03/CeO2 thin films (high content of CeO2) in the frequency region where the capacitance is constant is associated with the lead resistance according to Street et al (1971). The optical energy gap of the films varies with the composition in same way as in doped crystalline semiconductors. The value of the, optical W03/Ce02 was calculated using the Davis and Mott (1970) formula for non-direct optical transitions. The capacitance of SiO/TeO2 thin films is found to be almost independent of frequency as well as of temperature. This is due to a strong ionic bonding which characterises a good insulator. The optical absorption edge of SiO/TeO2 is found to be sharper than that of W03/ CeO2 and very similar to that found in most crystalline solids. The value of the optical energy gap is calculated using the same formula as in W03/CeO2. The systematic change of the optical gap with composition is observed only in a limited range of compositions. The a. c electrical properties of W03/Te02 amorphous thin films are described using the Springett(1974) and Elliott(1977) models. The optical absorption edge of WO3/TeO2 is found to lead to new arguments about the origin of the Urbach edges.The a. c electrical conductivity shows a frequency dependence of the form as ca wS in all samples studied in the present work. The mechanism of conduction at low temperatures with the index varying from 0.5 to I is thought to be due to hopping of electrons between localized states in the gap. At high fields the d. c current shows a non-linear dependence on the applied electric field. This is thought to be due to either space charge or Schottky effects in the oxides containing transition metal ions. In SiO/TeO2 dielectric films, the non-linear dependence of current on the electric field is thought to be due to either the Poole-Frenkel effect or at slightly lower fields it could be due to impurities.

No description available.