Optical characterization of emerging electronic and ferroelectric materials and structures




Cho, Yujin

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My Ph. D. work is on altering material properties to improve or apply in device applications and probing the manipulated properties through linear/ nonlinear optical methods. I focused my study on three types of structural modifications. First, in Chapter 2, I applied strain on a 3D integrated silicon circuit structure and BaTiO₃ thin film. Silicon, well-understood bulk material and most popular semiconductor platform, acquires new electronic and optical properties under strain. In addition, one can significantly control the ferroelectric and electro-optic properties of BaTiO₃ thin film, a traditional perovskite ferroelectric, by applying strain via a piezoelectric substrate, as shown in Chapter 5. Second, I engineered well-characterized bulk materials into thin films, as thin as 1 nm. In Chapter 4, I measured retention time of ferroelectric polarization on BaTiO₃ film thicknesses in the range of 10-20 nm. In addition, the thickness of the layers of a 2D material, e.g. In₂Se₃, introduces variations in bandgaps, dielectric functions, and/or absorption, which will be shown in Chapter 6. Lastly, I characterized the displacive and disorder-to-order transitions in ferroelectric materials. For example, in Chapter 3, we discovered order-disorder ferroelectric mechanism in double perovskites synthesized by Spark-plasma-sintering method and studied their Curie temperatures. Through these projects, I discovered new ways of controlling material properties and studied their underlying origins of the emerging phenomena using optical methods



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