Wide band gap oxide-semiconductor heterostructures grown by molecular beam epitaxy

Wide band gap oxides and semiconductors will have tremendous impact on future energy efficient and environmentally sustainable electronics. Wide gap semiconductors like GaN and AlGaN are important in light emitting diode applications and for high-frequency telecom and radar applications like base stations for upcoming 5G networks. Further, these materials along with some wide band gap semiconducting oxides like Ga₂O₃ may prove to be invaluable for medium to high power electronics applications, starting from switching power supplies used to charge batteries in consumer devices like smartphones and laptops, to high-power supplies that can charge electric car batteries and are suitable for electric grid and power transmission line applications. Basic materials studies of these material systems are therefore in high demand. In this dissertation I will present materials studies on wide band gap oxide thin films grown by molecular beam epitaxy on crystalline semiconductor substrates. The oxide thin films are characterized with regards to epitaxial structure and electronic structure by electron and x-ray diffraction techniques, by photoelectron spectroscopy and in collaboration with researchers from UT Dallas, Arizona State University, Rutgers University and University of Turku by transmission electron microscopy, inverse photoemission spectroscopy and scanning tunneling spectroscopy. Two materials systems are discussed in detail: 1. The rare-earth sesquioxide Eu₂O₃ in regards to potential gate-dielectric applications on the wide band gap semiconductor GaN. The focus of the studies were interface quality, structural quality, and band offsets; and the electronic structure of Eu₂O₃ to determine the band gap and understand the influence of Eu 4f states on the band gap of Eu₂O₃. 2. The structural integration of ultra-wide band gap oxide semiconductor Ga₂O₃ on a standard Si semiconductor substrate. Epitaxial integration of Ga₂O₃ with the workhorse of semiconductors Si can enable cost-reduction & monolithically-integrated devices. The focus of the studies was the structural characterization of the Ga₂O₃ layers grown by plasma-assisted molecular beam epitaxy.Physic