University of SaskatchewanHARVEST
  • Login
  • Submit Your Work
  • About
    • About HARVEST
    • Guidelines
    • Browse
      • All of HARVEST
      • Communities & Collections
      • By Issue Date
      • Authors
      • Titles
      • Subjects
      • This Collection
      • By Issue Date
      • Authors
      • Titles
      • Subjects
    • My Account
      • Login
      JavaScript is disabled for your browser. Some features of this site may not work without it.
      View Item 
      • HARVEST
      • Electronic Theses and Dissertations
      • Graduate Theses and Dissertations
      • View Item
      • HARVEST
      • Electronic Theses and Dissertations
      • Graduate Theses and Dissertations
      • View Item

      Optical properties of amorphous selenium films

      Thumbnail
      View/Open
      Revised_Optical_Properties_of_Amorphous_Selenium_Films.pdf (1.380Mb)
      Date
      2006-06-26
      Author
      Tan, W. C. (Wee Chong)
      Type
      Thesis
      Degree Level
      Masters
      Metadata
      Show full item record
      Abstract
      Recently there has been a substantial renewed interest in the electrical and optical properties of amorphous selenium (a-Se) films due to its use as an ultra-sensitive photoconductor in the newly developed flat panel x-ray image detector and high definition digital and video camera. This project has examined the optical properties of a range of a-Se films fabricated by conventional vacuum deposition technique. The films were deposited at two substrate temperatures called hot and cold deposition: (i) at 51°C, which is above the glass transition temperature (Tᵍ ≈ 40°C), and (ii) at 3°C, well below the glass transition temperature. The transmission spectrum T(λ) of all the a-Se films were measured over a wide range of wavelengths from 500 nm to 2500 nm, and analyzed using the Swanepoel technique. The thickness, absorption coefficient a(λ) refractive index n(λ), and optical bandgap, EgT and EgU, in different absorption regions of a-Se were all extracted using the Swanepoel technique. A systematic way to improve the accuracy of the calculations was also developed and the n vs.  data was fitted to the Sellmeier dispersion equation. The optical bandgap EgT was obtained from the h vs h plot of the absorption spectrum and the Urbach tail was obtained from a semi-logarithmic plot of  vs h. With all essential optical properties collected, the influence of thermal annealing, the deposition temperature, doping, thickness and aging time on the optical properties of a-Se films was studied. Amorphous selenium is essentially a glass, and all glasses exhibit some degree of structural relaxation effects during which the physical properties such as the refractive index and the bandgap change with time, called "aging". First of all, thermal annealing an a-Se film at T = 51°C for an hour reduces the thickness by ~15% and increases the refractive index by ~0.5%. The optical bandgap does not change by more than 0.2%. While the decrease in the thickness is thought to be due to the rearrangement of the molecular clusters and the amorphous network, the increase in the refractive index is believed to be linked to the densification and the polarizability of the material. Although the influence of the thickness of the film, the temperature of the glass substrate, and the doping of 67ppm of chlorine on the optical properties of the a-Se film was found to be negligible, there are noticeable changes during aging. It was found that an aged a-Se film that was cold deposited has an increased refractive index that is believed to be caused by densification alone. In a period of 2 months, the thickness of a cold deposited a-Se:67ppm-Cl film shrinks by 3.5% and the refractive index increases by 3.7%. The optical bandgap of the film decreases by 0.6%. Similar aging trends in the thickness, the refractive index, and the optical bandgap were also observed in a cold deposited a-Se film but no significant changes, at least not more than 0.5% deviation, were noted in a period of about 1-3 weeks in any aging a-Se films that were hot deposited or annealed.
      Degree
      Master of Science (M.Sc.)
      Department
      Electrical Engineering
      Program
      Electrical Engineering
      Supervisor
      Kasap, Safa O.; Johanson, Robert E.
      Copyright Date
      June 2006
      URI
      http://hdl.handle.net/10388/etd-07032006-182757
      Collections
      • Graduate Theses and Dissertations
      University of Saskatchewan

      University Library

      The University of Saskatchewan's main campus is situated on Treaty 6 Territory and the Homeland of the Métis.

      © University of Saskatchewan
      Contact Us | Disclaimer | Privacy