Elliott Ortmann, UT-Austin

"Optical and Electro-Optical Phenomena in Transition Metal Oxide Thin Film Heterostructures"

Abstract: Beginning in the mid-20th-Century and continuing to the present day, integrated circuit technology has advanced at a remarkable pace. Dedicated materials research has been at the heart of this advancement, with materials development preceding technological advancement at nearly every stage. As humanity barrels onward into the 21st-Century and our data and computational demands grow ever larger, new computing hardware designed to handle increasingly difficult computational challenges is quickly becoming necessary in order to continue the historical breakneck pace of advancement. Just as in the early days of the integrated circuit, materials advancement will likely be the key to developing the next generation of computing hardware.
In this thesis, I investigate two materials systems well-suited for implementation in next-generation optical computing technologies: transition metal oxide quantum wells and Pockels-active BaTiO₃ thin film heterostructures. Both materials systems are promising for use in a wide variety of optical and electro-optical devices central to integrated photonic technologies, including quantum cascade lasers, photodetectors, electro-optic modulators and switches.

For the case of transition metal oxide quantum wells, I focus on the famous SrTiO₃/LaAlO₃ materials system. I first investigate the structural and optical properties of arbitrarily thick, high-quality SrTiO₃/LaAlO₃ heterostructures grown on oxide substrates. Then, I demonstrate the monolithic integration of these heterostructures on silicon, bringing them one step closer to technological relevance. Finally, I present detailed simulations of the optical and electro-optical performance of integrated photonic devices based on SrTiO₃/LaAlO₃ heterostructures.

In bulk form, the transition metal oxide BaTiO₃ has some of the largest known Pockels coefficients. However, early work suggests the coefficients are reduced by roughly a factor of ten when fabricated as a thin film. Here, I demonstrate the first BaTiO₃-based integrated devices showing bulk-like Pockels coefficients. Then, I iterate on the initial design of the devices in order to optimize them for ultra-low-power refractive index tuning. The resulting devices achieve refractive index tuning with power consumption many orders of magnitude less than previous reports. Taken together, the investigations in this thesis will hopefully open the door for the development of new kinds of optical and electro-optical devices for use in integrated photonics technologies.