Growth, characterization, and applications of lanthanide monopnictide nanoparticles and films in and on III-V semiconductors
Date
2016
Authors
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Publisher
University of Delaware
Abstract
Lanthanide monopnictides have properties that makes them interesting for many applications including thermoelectrics and photoconductive switches. Despite their usefulness, many of their fundamental properties remain unknown. This dissertation explores the fundamental properties of TbAs, both as nanoparticles and films. This dissertation also presents a novel lanthanide monopnictide nanocomposite as a possible candidate material for photoconductive switches. ☐ To study the electronic structure of TbAs we used fluence dependent optical pump terahertz probe measurements, revealing that TbAs nanoparticles saturate and are likely semiconductors. Spectrophotometry shows a large blue shift in the optical absorption energy when the matrix is changed from In0.53 Ga0.47As to GaAs. To explore these differences, temperature dependent Hall effect measurements are utilized, revealing that TbAs: In 0.53Ga0.47As is degenerately doped while TbAs:GaAs has the Fermi level located near the center of the GaAs band gap. These combined measurements indicate that TbAs forms a type I (straddled) heterojunction with GaAs and a type II (staggered) heterojunction with In0.53Ga0.47As. ☐ The study of TbAs nanoparticles revealed that TbAs is a semiconductor, but the band gap energy remains unknown. Films of TbAs were grown in an attempt to determine the band gap. Spectrophotometry reveals the optical band gap is dependent upon film thickness. Additionally, Hall effect measurements show that the films are degenerately doped with the carrier concentration also depending on thickness. Degenerately doping causes a Burstein-Moss shift in the optical absorption where the magnitude of the shift depends on carrier concentration, and thus thickness. ☐ In addition to studying the fundamental properties of TbAs, this dissertation explores ErAs:GaBiAs as a novel candidate material for photoconductive switches. Spectrophotometry measurements reveal that bismuth reduces the band gap, as expected, allowing these materials to be pumped with fiber-coupled lasers. Hall effect measurements reveal that ErAs pins the Fermi level within the band gap; resulting in a high dark resistance while maintaining a high mobility. The ErAs nanoparticles also provide a carrier recombination pathway that results in a short carrier lifetime, shown by transient absorption optical pump optical probe measurements. These measured properties show that ErAs:GaBiAs is a promising choice for fiber-couple photoconductive switches.