Transparent conducting oxides (TCO) are a unique class of compounds that combine the properties of being optically transparent but at the same time are electrically conductive. TCOs are used in a variety of applications such as transparent contacts for solar cells, electrochromic windows, low-e windows, optoelectronic devices, light-emitting diodes, optical displays, UV sensors, defrosting windows, etc. By controlling doping and by adjusting the donor/acceptor levels, the conductivity of TCOs can be tuned from insulating via semiconducting to conducting. Various properties of TCOs such as optical transparency, bandgap, and electrical conductivity can be controlled using the aforementioned process. This concept paved the way for the discovery of p-type and n-type semiconducting transparent thin films. Some of the well-known TCOs include SnO2, Sn-doped In2O3 (Indium Tin Oxide - ITO), In2O3, Sc-doped ZnO, Al-doped ZnO (Aluminum doped ZnO - AZO), and CdSnO2. However, the aforementioned TCOs are classified as n-type in nature. A combination of p- and n-type transparent conducting channels are used as active layers in transparent optoelectronic devices. P-type TCOs have been known to either depict good optical transparency or good electrical conductivity, unlike n-type TCOs which typically exhibit both properties at the same time. Hence, it has been extremely difficult to synthesize a p-type TCO which has the right balance between conductivity and transparency. To alleviate this issue, researchers came up with a new concept of 'Chemical Modulation of Valence Band (CMVB)'. This gave rise to a new class of materials called delafossites. Delafossites, especially Cu-based delafossites, are known to exhibit p-type nature, acceptable electrical conductivity, and good optical transparency simultaneously. Cu-based delafossites have a chemical formula of CuMO2, where Cu is the positive monovalent cation (Cu+), M = Al3+, Cr3+, In3+, Ga3+, Sc3+, and Y3+ (trivalent cation), and oxygen is the divalent anion (O2?). Amongst the Cu-based delafossite family, p-type CuInO2 displays the highest optical bandgap and CuCrO2 presents the highest electrical conductivity. To propel the motive toward the research on novel p-type TCOs, this dissertation focuses on the deposition, optimization, synthesis, and post-deposition characterization of CuInO2 and CuCrO2 thin films. The thin films were deposited using either single or dual-target RF magnetron sputtering technique of either Cu and In targets (used for single-target sputtering) or Cu, In2O3, Cu2O, and Cr2O3 (used for dual-target sputtering). By varying the deposition parameters or the post-deposition treatment processes, thin films with varying compositions and properties were obtained. Using the single target sputtering approach, an orthorhombic phase of copper indium oxide (Cu2In2O5), was also synthesized and researched. Transparent diodes are next-generation electronic devices that can be embedded into the windows of commercial and domestic buildings, solar panels, etc. The feasibility of CuCrO2-based transparent pn-junction diodes was studied and reported in this dissertation. A transparent antibacterial thin film can be applied to the touch panels of the information terminals used in hospitals, smartphones, department stores, etc. The practicality of CuCrO2 as a transparent antibacterial thin film has also been studied in this dissertation.
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Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Electrical and Computer Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Sreeram Sundaresh, FNU, "Process Optimization and Characterization of p-type Copper Indium Oxide and Copper Chromium Oxide Transparent Conducting Thin Films and its Applications" (2023). Electronic Theses and Dissertations, 2020-. 1670.