Close-Spaced Vapor Transport Using HCL as Transport Agent - Process Capability Studies for Growth of III-V Films and Devices
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Date
2020-02-27
Authors
Funch, Christopher
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Publisher
University of Oregon
Abstract
The price of photovoltaic (PV) modules has continued to drop in recent decades and the normalized cost ($/kW) is approaching that of some fossil fuel sources. Two fundamental components of the final PV cost are the efficiency of the system and the materials/fabrication cost necessary to produce it. Today, roughly 95% of all PV modules are produced from Si primarily due to the maturity of the Si microelectronics industry. Historically, PV modules made from III-V materials have limited applications, almost exclusively in either aerospace or concentrator applications, due to their record efficiencies but higher costs. A reduction in cost to produce III-V PVs could enable a greater number of aerospace applications and reduced costs in capturing renewable energy terrestrially. However, current manufacturing techniques for producing high-quality III-V materials require expensive precursors, have high capital costs, and reduced throughput. Close-spaced vapor transport (CSVT) is an alternative, low-cost technique but has not been fully developed. This work describes the use of HCl as a transport agent (Cl-CSVT) to understand and expand the capabilities of this technique in a re-engineered system.
Prior research demonstrated GaAs devices using water vapor as the transport agent (H2O-CSVT). Devices made using this strategy showed good electronic quality and comparable efficiencies with other deposition techniques. However, oxide related defects and inaccessibility to some material systems (i.e. Si and Al) limit the capabilities of H2O-CSVT. Chapter I further describes the motivation and basic theory behind this growth technique. Chapter II describes the design details of the Cl-CSVT reactor along with the procedures used for growths in the subsequent chapters. Chapter III gives details on the process conditions favorable for growth and the characterization of films prior to their integration into fabricated PV devices. Chapter IV explores the reproducibility of PV devices compared with those by H2O-CSVT. Chapter V highlights proof-of-principle capabilities of this system beyond H2O-CSVT. Chapter VI discusses possible future directions to improve upon the design of the Cl-CSVT system to better enable the use of some material systems investigated and make the system more commercially viable.
This dissertation includes previously published and unpublished co-authored material.
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Keywords
Close-Spaced Vapor Transport, Epitaxy, GaAs, III-V, Low-Cost, Photovoltaics