TITLE

Charge-transfer absorption band in Zn1-xMxO (M: Co, Mn) investigated by means of photoconductivity, Ga doping, and optical measurements under pressure

AUTHOR(S)
Gilliland, S. G.; Sans, J. A.; Sánchez-Royo, J. F.; Almonacid, G.; Segura, A.
PUB. DATE
June 2010
SOURCE
Applied Physics Letters;6/14/2010, Vol. 96 Issue 24, p241902
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
The nature of the charge-transfer absorption band in undoped and Ga-doped Zn1-xMxO (M: Co, Mn) thin films is investigated by means of photoconductivity and optical absorption measurements under pressure. Internal transitions in the crystal field split Co 3d shell do not contribute to the photoconductivity spectrum and have very low pressure coefficient. Broad absorption bands at photon energies just below the band gap in both ZnMnO and ZnCoO clearly contribute to the photoconductivity spectra, indicating that they create free carriers and are consequently charge-transfer transitions. Under pressure, charge transfer bands have a pressure coefficient close to or larger than the band gap, in contrast to the expected low or negative pressure coefficient in a valence-band-to-localized level transition. Finally, the expected Burstein–Moss shift in the fundamental edge of heavily Ga-doped samples of ZnMO is associated to a larger shift and intensity decrease in the pre-edge band, confirming that charge-transfer transitions in ZnMO should be ascribed to transitions from the Co or Mn 3d shell to the conduction band.
ACCESSION #
51526958

 

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