Title page for ETD etd-05022002-145350

Type of Document Dissertation
Author Vijarnwannaluk, Sathon
Author's Email Address vsathon@vt.edu, vsathon@hotmail.com
URN etd-05022002-145350
Title Optical studies of GaAs:C grown at low temperature and of localized vibrations in normal GaAs:C
Degree PhD
Department Physics
Advisory Committee
Advisor Name Title
Zallen, Richard H. Committee Chair
Di Ventra, Massimiliano Committee Member
Heflin, James R. Committee Member
Indebetouw, Guy J. Committee Member
Ritter, Alfred L. Committee Member
  • carbon-doped
  • infrared
  • gallium arsenide
  • LT-GaAs
  • Raman
  • localized vibrational mode
  • photoluminescence
  • GaAs
  • GaAs:C
Date of Defense 2002-04-25
Availability unrestricted
Optical studies of heavily-doped GaAs:C grown at low temperature by molecular beam epitaxy were performed using room-temperature photoluminescence, infrared transmission, and Raman scattering measurements. The photoluminescence experiments show that in LT-GaAs:C films grown at temperatures below 400 C, nonradiative recombination processes dominate and photoluminescence is quenched. When the growth temperature exceeds 400 C, band-to-band photoluminescence emission appears. We conclude that the films change in character from LT-GaAs:C to normal GaAs:C once the growth temperature reaches 400 C. Annealing, however, shows a different behavior. Once grown as LT-GaAs:C, this material retains its nonconducting nonluminescing LT characteristics even when annealed at 600 C. The Raman-scattering measurements showed that the growth temperature and the doping concentration influence the position, broadening, and asymmetry of the longitudinal-optical phonon Raman line. We attribute these effects to changes in the concentration of interstitial carbon in the films. Also, the shift of the Raman line was used to estimate the concentration of arsenic-antisite defects in undoped LT-GaAs. The infrared transmission measurements on the carbon-doped material showed that only a fraction of the carbon atoms occupy arsenic sites, that this fraction increases as the growth temperature increases, and that it reaches about 100% once the growth temperature reaches 400 C. The details of all these measurements are discussed.

Infrared transmission and photoluminescence measurements were also carried out on heavily-doped GaAs:C films grown by molecular beam epitaxy at the standard 600 C temperature. The infrared results reveal, for dopings under 5 x 1019 cm-3, a linear relation between doping concentration and the integrated optical absorption of the carbon localized-vibrational-mode band. At higher dopings, the LVM integrated absorption saturates. Formation of CAs-CAs clusters is proposed as the mechanism of the saturation. The photoluminescence spectra were successfully analyzed with a simple model assuming thermalization of photoelectrons to the bottom of the conduction band and indirect-transition recombination with holes populating the degenerately doped valence band. The analysis yields the bandgap reduction and the Fermi-level-depth increase at high doping.

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