Optical Properties of a Magnetic Semiconductor: Chalcopyrite CuFeS2.: I. Absorption Spectra of CuFeS2 and Fe-Doped CuAlS2 and CuGaS2

Optical absorptions have been measured in chalcopyrite, CuFeS 2 , and Fe-doped CuAlS 2 and CuGaS 2 . An extra absorption band with two peaks is observed at the low energy region of the absorption edge for Fe-doped CuAlS 2 and CuGaS 2 .Energy positions of two absorption peaks are 1.3 eV and 2.0 eV for CuAlS 2 and 1.2 eV and 1.9 eV for CuGaS 2 , respectively. The intensity of this absorption band increases with the increase of doped Fe ions and grows into the absorption edge of CuFeS 2 . Its oscillator strength comes up to 7·10 -2 . In chalcopyrite photoconductivity is observed and its maximum is just at the same energy region of the absorption edge. By comparing our results with those of absorption measurements for Cu- or Fe-doped ZnS it is concluded that this absorption band originates from the charge transfer transitions relating to 3d electron of Fe ions and the absorption edge of CuFeS 2 rises from the band-to-band transition corresponding to this charge transfer transition.