Events at Physics
Events on Tuesday, October 18th, 2022
- Thesis Defense
- Characterizations of ultrathin interfacial atomic-layer-deposited oxides and nitrides for semiconductor grafting applications
- Time: 8:00 am
- Place: EH 4610 in Engineering Hall
- Speaker: Jiarui Gong, Physics Graduate Student
- Abstract: Lattice-mismatched heterogeneous semiconductor grafting technique has been developed recently to combine lattice-mismatched semiconductors and create innovative devices. An ultrathin oxide (UO) deposited by atomic layer deposition (ALD) at the grafted interface has been recognized as a passivation and tunneling layer, which plays an important role in improving the junction performance, such as achieving higher on/off ratio and lower ideality factor in a pn junction. To better understand the influence of the ALD UO, various experiments have been conducted to characterize some electrical properties of the ALD UO in various semiconductor systems. In the first part of the presentation, the history of semiconductor heterostructures and the development of semiconductor grafting technique are reviewed. In the second part, the interfaces between the UO and several semiconductors were characterized by X-ray photoelectron spectroscopy (XPS). Various electron states were observed through peak fitting. The correlation between the passivation effect and the electron states was established. In the third part, the surface band-bending of c-plane Ga-face GaN with various UO/UN layers was characterized by XPS measurements. The valence band offset (VBO) between GaN and the UO/UN was calculated from the GaN valence band spectra. The possibility of fabricating an AlGaAs/GaAs/GaN npn heterojunction bipolar transistor (HBT) was examined through simulation. In the last part, a novel releasing and transfer printing method of the single-crystalline AlN nanomembrane (NM) was introduced. The properties of the AlN were characterized both before and after the whole process and no degradation was observed. The possibility of obtaining high-quality single-crystalline AlN NM brings new potentials to the semiconductor grafting technique.
- Host: Zhenqiang Ma, Mark Rzchowski
- Theory Seminar (High Energy/Cosmology)
- Statistical significances and projections for proton decay experiments
- Time: 4:00 pm - 5:00 pm
- Place: Chamberlin 5280
- Speaker: Prudhvi Bhattiprolu, University of Michigan
- Abstract: The projected discovery and exclusion capabilities of particle physics and astrophysics/cosmology experiments are often quantified using the median expected significance. We argue that this criterion leads to flawed results, which for example can counterintuitively project lessened sensitivities if the experiment takes more data or reduces its background. We advocate for standard use of the “exact Asimov” criterion detailed in this talk. Various counterintuitive flaws associated with frequentist and modified frequentist statistical measures of significance for multi-channel counting experiments are discussed in a general context and illustrated with examples. We argue in favor of conservative Bayesian-motivated statistical measures, and as an application we employ these measures to obtain the current lower limits on proton partial lifetime at various confidence levels, based on Super-Kamiokande's data, generalizing the 90% CL published limits. Finally, we present projections for exclusion and discovery reaches for proton partial lifetimes in p → ν K+ and p → e+ π0 decay channels at Hyper-Kamiokande, DUNE and JUNO.
- Host: George Wojcik