| dc.description.abstract | This thesis investigates the efects of laser processing of transparent semiconductor thin flms. Detailed in this work, are three developments in the felds of ultrafast science and condensed matter relating to: (1) experimental femtosecond laser pre-annealing of solution-based ZTO flms deposited on an SiO2/Si substrate, (2) experimental femtosecond laser post-annealing of rf-sputtered ZnO flms deposited on an SiO2/Si substrate, and (3) experimental femtosecond laser post-annealing of ultrathin ITO flms deposited on a PET substrate.
(1) Current research emphasizes sustainable, additive, solution-based large-area electronics compatible with roll-to-roll (R2R) manufacturing. Zinc tin oxide (ZTO) is a key material candidate that ofers resource abundance and favorable optoelectronic properties. Although, as-deposited sol-gel ZTO is porous, mechanically fragile, and contains residual organics. In this work, we report the implementation of deep ultraviolet (DUV) femtosecond laser light to efectively convert the precursor sol-gel flm into a high quality metal oxide. Utilizing characterization techniques and analysis of the irradiated flms, it is observed that ultrafast laser processing removes organic structures, condenses, and modifes the stoichiometry of the ZTO flms, notably while maintaining an amorphous phase desirable for fexible electronics.
(2) Owing to their controllable conductivity, competitive carrier mobility, and high transparency to visible wavelengths, transparent conductive oxides (TCOs) have versatile applications in displays, solar cells, UV photodetectors, and gas sensors. Zinc oxide (ZnO) has gained popularity for these applications owing to its resource abundance, wide direct bandgap, and stable exciton binding energy. Although, magnetron-sputtered ZnO contains defects and crystalline stress that hinder both optical and electrical properties. In this work, we utilize DUV femtosecond laser light to re-crystallize ZnO flms to promote atomic lattice rearrangement into a higher quality metal oxide framework. Investigation of the irradiated flms with characterization techniques and analysis reveals that ultrafast laser post-processing induces grain re-growth to larger grain sizes, relieves as-deposited tensile strain, and provides stoichiometric control of the sputtered ZnO flms.
(3) For fexible electronic designs, the substrate has to be carefully selected, providing a blend of favorable mechanical, electrical, optical, and chemical properties for desired application. Polyethylene terephthalate (PET), particularly, showcases decent toughness, high transparency to visible wavelengths, and great mechanical compatibility with the human body at the price of a very low thermal budget. Indium tin oxide (ITO) shows promise for "invisible" electronic applications due to its wide bandgap, low resistivity, and high transparency. Although, high-temperature post-annealing processes used to efectively promote ITO optoelectronic properties are incompatible with polymer-based substrates. Alternatively, in this work, we utilize DUV femtosecond laser light to crystallize an ultrathin ITO flm layer without structurally damaging the underlying PET substrate. | en_US |
