Optimization and Characterization of Low-Cost Substrates for III-V Photovoltaics

The highest achieved photovoltaic power conversion efficiency (approximately 47% under concentration) is available from III-V multijunction solar cells made from subcells of descending bandgap that optimize light collection from the solar spectrum. Unfortunately, both III-V multijunction and single-junction solar cells are expensive, limiting their use to niche concentration or space power applications and precluding their competitiveness in the terrestrial flat-plate market. The majority of the III-V solar cell cost is attributed to the thick, monocrystalline substrates that are used as a platform for epitaxial growth, and to the throughput, precursors, and utilization of those precursors associated with traditional growth reactors. Significant cost reduction to approach $1/W for total photovoltaic system cost is imperative to realize III-V solar cells that are cost-competitive with incumbent silicon solar cells, and can include techniques to develop inexpensive substrates directly; enable multiple reuses of a pristine, expensive substrate without the need for polishing; and enhance the throughput by increasing the semiconductor growth rate during epitaxy. This dissertation explores two main techniques to achieve low-cost substrates for III-V photovoltaics: aluminum-induced crystallization to create polycrystalline germanium thin films, and remote epitaxy through graphene to enable monocrystalline substrate reuse without polishing. This dissertation also demonstrates record III-V growth rates exceeding 0.5 mm/h using a potentially lower-cost III-V growth technique, which would increase throughput in production reactors. The ability to reduce the costs associated with both substrates and epitaxy will be imperative to decreasing the total system cost of III-V PV

The Perfect Storm: Strategies for Weathering Change in Technical Services

This paper describes the approach to three simultaneous problems faced by technical services at the College of Charleston Libraries: the retirement of the department head, the outbreak of the COVID-19 pandemic, and the migration to a new library management system

Description and catalog of ionospheric F-region data, Jicamarca Radar Observatory, November 1966 - April 1969

Equatorial ionospheric F-region data reduced from the Jicamarca Radar Observatory (JRO) incoherent scatter observations for particular periods is described. It lists in catalog form the times of the observations made during those periods. These F-region data include the electron concentration and the electron and ion temperatures. The data were inferred from the incoherent scatter observations of JRO

MAGMO: Coherent magnetic fields in the star forming regions of the Carina-Sagittarius spiral arm tangent

We present the pilot results of the `MAGMO' project, targeted observations of ground-state hydroxyl masers towards sites of 6.7-GHz methanol maser emission in the Carina-Sagittarius spiral arm tangent, Galactic longitudes 280 degrees to 295 degrees. The `MAGMO' project aims to determine if Galactic magnetic fields can be traced with Zeeman splitting of masers associated with star formation. Pilot observations of 23 sites of methanol maser emission were made, with the detection of ground-state hydroxyl masers towards 11 of these and six additional offset sites. Of these 17 sites, nine are new detections of sites of 1665-MHz maser emission, three of them accompanied by 1667-MHz emission. More than 70% of the maser features have significant circular polarization, whilst only ~10% have significant linear polarization (although some features with up to 100% linear polarization are found). We find 11 Zeeman pairs across six sites of high-mass star formation with implied magnetic field strengths between -1.5 mG and +3.8 mG and a median field strength of +1.6 mG. Our measurements of Zeeman splitting imply that a coherent field orientation is experienced by the maser sites across a distance of 5.3+/-2.0 kpc within the Carina-Sagittarius spiral arm tangent.Comment: 19 pages, 13 figures, accepted for publication in MNRA