No description available.

Crystalline indium oxide nanowires were synthesized following optimization of growth parameters. Oxygen vacancies were found to impact the optical and electronic properties of the as-grown nanowires. Photoluminescence measurements showed a strong U.V emission peak at 3.18 eV and defect peaks in the visible region at 2.85 eV, 2.66 eV and 2.5 eV. The defect peaks are attributed to neutral and charged states of oxygen vacancies. Post-growth annealing in oxygen environment and passivation with sulphur are shown to be effective in reducing the intensity of the defect induced emission. The as-grown nanowires connected in an FET type of configuration shows n-type conductivity. A single indium oxide nanowire with ohmic contacts was found to be sensitive to gas molecules adsorbed on its surface.

<p dir="ltr">As silicon (Si) technology advances to 3 nm node and beyond, vertically stacking in 3D is considered as the primary choice to increase the density of transistors per unit area for better chip performance. Therefore, looking for new materials capable of replacing Si in back-end-of-line (BEOL) compatible monolithic 3D (M3D) integration has become one of the most important topics in the current field of electronic devices. Recent developed atomic layer deposition (ALD) deposited indium oxide (In₂O₃) field-effect transistors (FETs) have realized excellent electrical performance including field effect mobility over 100 cm²/V·s, on/off ratio up to 10¹⁷ and on-state current (I_ON) over 2.5 mA/μm in nanometer thin In₂O₃ FETs, providing promising prospect for next generation electronics. In this thesis, four main In₂O₃ related topics are discussed to examine the practicality of ALD In₂O₃ as channel material in BEOL compatible applications. First, the bias stability of planar In₂O₃ transistors and the effect of tin doping are studied. Second, gate-all-around (GAA) In₂O₃ FETs are implemented to improve I_ON up to record high 20 mA/μm, and its reliability is systematically measured and analyzed. Third, multilayer In₂O₃ FETs are constructed to investigate the possibility of vertical stacking. Last, vertical full oxide transistors with In₂O₃ gate are demonstrated to prove the feasibility of potential 3D integration.</p>

Transparent thin film transistors fabricated at room temperature by radio frequency magnetron sputtering using indium oxide material system were proposed. The electrodes of the transparent thin film transistors were obtained by depositing indium oxide with 10% tim doping. Resistivity as low as 4¡Ñ10-4£[-cm at room temperature was achieved. The channel layers of the transparent thin film transistors were fabricated using pure indium oxide target in an Argon and oxygen environment. Resistivity larger than 10-5£[-cm was obtained with 60% oxygen partial pressure. Silicon nitride prepared by room temperature radio frequency sputtering were used for the gate dielectric layer with low leakage current. Environmental-safe lift-off processes were used to fabricated the electrodes, the isolation layer, and the channel layer. The transistor characteristics were obtained by standard I-V measurement. The on-off ratio of the 30£gm ¡Ñ 150£gm transparent thin film transistor is 100.

The aim of this thesis is to provide an in-depth investigation of zinc tin oxide, Zn1-xSnxOy or ZTO, grown by atomic layer deposition (ALD) as a buffer layer in Cu(In,Ga)Se2 (CIGS) solar cells. The thesis analyzes how changes in the ALD process influence the material properties of ZTO, and how these in turn affect the performance of CIGS solar cells. It is shown that ZTO grows uniformly and conformably on CIGS and that the interface between ZTO and CIGS is sharp with little or no interdiffusion between the layers. The band gap and conduction band energy level of ZTO are dependent both on the [Sn]/([Zn]+[Sn]) composition and on the deposition temperature. The influence by changes in composition is non-trivial, and the highest band gap and conduction band energy level are obtained at a [Sn]/([Zn]+[Sn]) composition of 0.2 at 120  °C. An increase in optical band gap is observed at decreasing deposition temperatures and is associated with quantum confinement effects caused by a decrease in crystallite size. The ability to change the conduction band energy level of ZTO enables the formation of suitable conduction band offsets between ZTO and CIGS with varying Ga-content. It is found that 15 nm thin ZTO buffer layers are sufficient to fabricate CIGS solar cells with conversion efficiencies up to 18.2 %. The JSC is in general 2 mA/cm2 higher, and the VOC 30 mV lower, for cells with the ZTO buffer layer as compared to cells with the traditional CdS buffer layer. In the end comparable efficiencies are obtained for the two different buffer layers. The gain in JSC for the ZTO buffer layer is associated with lower parasitic absorption in the UV-blue region of the solar spectrum and it is shown that the JSC can be increased further by making changes to the other layers in the traditional CdS/i-ZnO/ZnO:Al window layer structure. The ZTO is highly resistive, and it is found that the shunt preventing i-ZnO layer can be omitted, which further increases the JSC. Moreover, an additional increase in JSC is obtained by replacing the sputtered ZnO:Al front contact with In2O3 deposited by ALD. The large gain in JSC for the ZTO/In2O3 window layer stack compensates for the lower VOC related to the ZTO buffer layer, and it is demonstrated that the ZTO/In2O3 window layer structure yields 0.6 % (absolute) higher conversion efficiency than the CdS/i-ZnO/ZnO:Al window layer structure.

n-type binary compound semiconductors such as InN, InAs, or In2O3 are especial because the branch-point energy or charge neutrality level lies within the conduction band. Their tendency to form a surface electron accumulation layer prevents the formation of rectifying Schottky contacts. Utilizing a reactive sputtering process in an oxygen-containing atmosphere, we demonstrate Schottky barrier diodes on indium oxide thin films with rectifying properties being sufficient for space charge layer spectroscopy. Conventional non-reactive sputtering resulted in ohmic contacts. We compare the rectification of Pt, Pd, and Au Schottky contacts on In2O3 and discuss temperature-dependent current-voltage characteristics of Pt/In2O3 in detail. The results substantiate the picture of oxygen vacancies being the source of electrons accumulating at the surface, however, the position of the charge neutrality level and/or the prediction of Schottky barrier heights from it are questioned.

No description available.

<p>As the miniaturization of the transistors in integrated circuits approaches the atomic scale limit, novel materials with exceptional performance are desired. Moreover, to conduct enough current with an ultrathin and small-scale body, high drain current density is preferably required. Nevertheless, devices may suffer seriously from self-heating effect (SHE) with high drain bias and current if the generated heat cannot be dissipated efficiently. In this thesis, we introduce two material systems and several techniques to accomplish the demand without SHE. Tellurium, as a van der Waals material composed by atomic helical chains, is able to realize its one-dimensional structure. We illustrate that the cross-sectional current density of 150 MA/cm2 is achieved through boron nitride nanotube (BNNT) encapsulation without SHE due to the superior thermal conductivity of BN. With the nanotube encapsulation technique applied, one-dimensional tellurium nanowire transistors with diameter down to 2 nm are realized as well, and single tellurium atomic chain is isolated. Furthermore, atomic-layer-deposited indium oxide (In2O3) as thin-film transistors exhibit even better current carrying capacity. Through co-optimization of their electrical and thermal performance, drain current up to 4.3 mA/μm is achieved with a 1.9-nm-thick body without SHE. The alleviation of SHE is due to a) the high thermal conductivity of the substrate assisting on efficiently dissipating the generated thermal energy, b) SHE avoidance with short-pulse measurement, and c) interface engineering between the channel stack and the substrate. These two material systems may be the solid solution to the desire of high current density transistors in the post-Moore era.</p>

n-type binary compound semiconductors such as InN, InAs, or In2O3 are especial because the branch-point energy or charge neutrality level lies within the conduction band. Their tendency to form a surface electron accumulation layer prevents the formation of rectifying Schottky contacts. Utilizing a reactive sputtering process in an oxygen-containing atmosphere, we demonstrate Schottky barrier diodes on indium oxide thin films with rectifying properties being sufficient for space charge layer spectroscopy. Conventional non-reactive sputtering resulted in ohmic contacts. We compare the rectification of Pt, Pd, and Au Schottky contacts on In2O3 and discuss temperature-dependent current-voltage characteristics of Pt/In2O3 in detail. The results substantiate the picture of oxygen vacancies being the source of electrons accumulating at the surface, however, the position of the charge neutrality level and/or the prediction of Schottky barrier heights from it are questioned.

In this work, we use optical techniques to provide insight into how various components within electrochemical cells can impart apparent heterogeneity to single gold nanoparticle electrodes. Optical methods are advantageous in comparison to traditional electrochemical techniques due to their high sensitivity and spatial resolution, allowing us to study the impact of heterogeneity with single nanoparticle and single molecule sensitivity. Throughout the course of this dissertation, two optical techniques are discussed in detail, dark-field microscopy, and single molecule fluorescence imaging. We first began by studying the impact of the substrate using dark-field microscopy to monitor the electrodissolution kinetics of gold nanoparticles on thin films of tin-doped indium oxide (ITO), which is a commonly used supporting electrode for correlated optical and electrochemical studies. We found that ITO from two different suppliers showed marked differences in the gold electrodissolution kinetics, with ITO from one of the suppliers even showing poor sample-to-sample reproducibility across substrates within the same lot number. These results showed that the supporting electrode cannot be ignored when performing single nanoparticle structure-function studies. In the second work, we analyzed the electrodissolution of gold nanoparticles on well-behaved ITO substrates to investigate heterogeneity in their electrodissolution kinetics. The rate constants associated with the electrodissolution of Au NPs were extracted by fitting the intensity-time traces to a first-order kinetic model. We found that a non-negligible population of Au NPs didn’t fit the predictive kinetics model leading us to further probe whether surface effects play a role in the electrodissolution process. Super-localization imaging was used to track the center position of the Au NPs as they electrodissolved revealing three distinct electrodissolution behaviors, and a mechanism for the electrodissolution of Au NPs was proposed. Furthermore, calcite-assisted localization and kinetics (CLocK) microscopy was used to visualize changes in anisotropy and provide information as to how the shape of the Au NP changes as it electrodissolves. Lastly, in our third work, we provide insight as to how heterogeneity from all the different components of a single nanoparticle electrochemical sample impacts the apparent electrode performance. We proposed dark-field microscopy and single molecule fluorescence imaging as tools capable of detangling these effects. Moreover, we established Cresyl Violet as a reporter of single molecule electrochemistry and developed a two-working electrode optical system capable of visualizing single molecule activity. Lastly, we explored the relationships between Au NP size, Cresyl Violet activity and Au NP electrodissolution and found no clear trend between them suggesting the need for more studies to deconvolute these effects and provide meaningful insight into the structure-property relationships. Overall, this dissertation highlights the complexity of single nanoparticle studies and how heterogeneity can be induced from all the components of an electrochemical cell. / Chemistry