dc.contributor.advisor McCluskey, Matthew D dc.creator Poole, Violet Mary dc.date.accessioned 2017-06-19T17:43:54Z dc.date.available 2017-06-19T17:43:54Z dc.date.issued 2016 dc.identifier.uri http://hdl.handle.net/2376/12070 dc.description Thesis (Ph.D.), Physics, Washington State University en_US dc.description.abstract Strontium titanate (SrTiO$_3$) is a transparent conducting oxide with a range of interesting properties, including a large, temperature-dependent dielectric constant and superconductivity at low temperatures. It has a wide indirect band gap of 3.2 eV at room temperature. Annealing in a reducing atmosphere with additional strontium oxide (SrO) powder at 1200$^\mathrm{o}$C results in the creation of native defects. These annealed samples show persistent photoconductivity (PPC) at room temperature, when exposed to light of energy 2.9 eV or greater. The three or more order of magnitude change in resistance persists long after the light is turned off. This effect is attributed to an electron being excited from an acceptor defect, with a large barrier for recapture, to the conduction band. This work investigates many of the changes that occur and factors that affect PPC. The right amount of SrO powder is crucial to the formation of PPC. The presence of some oxygen vacancies is also necessary for PPC; however, too many will mute the dramatic change in resistivity. Peaks at 430 nm and 520 nm appear in the visible region of the spectrum. The peak at 430 nm is due to iron, while the peak at 520 nm has not been identified. The infrared region of the spectrum also shows changes. First, the intensity of the transmitted signal drops significantly after light exposure, due to free carrier absorption. Additionally, a hydrogen line at 3500 cm$^{-1}$ and satellites are often observed in as-received samples. The satellites disappear during annealing and return during PPC. The hydrogen lines have the same thermal kinetics as the 520 nm peak. Hydrogen lines at 3355 and 3384 cm$^{-1}$, if present, will prevent PPC. An exposed chip can be erased (i.e. returned to its pre-light exposed state) by using a heat treatment. Erasing and polishing an annealed chip prior to light exposure can result in weakly $p$-type behavior with high mobility holes ( $>$ 100 cm$^2$/Vs). This is an order of magnitude higher than those commonly measured for electrons (5-10 cm$^2$/Vs). The average hole densities were in the 10$^9$-10$^{10}$ cm$^{-3}$ range, consistent with a deep acceptor. en_US dc.description.sponsorship Washington State University, Physics en_US dc.language.iso English dc.rights In copyright dc.rights Publicly accessible dc.rights openAccess dc.rights.uri http://rightsstatements.org/vocab/InC/1.0 dc.rights.uri http://www.ndltd.org/standards/metadata dc.rights.uri http://purl.org/eprint/accessRights/OpenAccess dc.subject Physics en_US dc.subject Materials Science en_US dc.subject Condensed matter physics en_US dc.subject Annealing en_US dc.subject EPR en_US dc.subject FTIR Spectra en_US dc.subject Persistant Photoconductivity en_US dc.subject Point Defects en_US dc.subject Strontium Titanate en_US dc.title Persistant Photoconductivity of Strontium Titanate dc.type Text dc.type Electronic Thesis or Dissertation
﻿