Spectral Dependence of the Photoconductance in CdCr2Se4

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Abstract
The spectral response of the photoconductance in In‐doped single crystals of the ferromagnetic semiconductor CdCr2Se4 was measured in the range of photon energies from 1 to 3 eV, between 80° and 340°K. The photoresponse is attributable to three distinct transitions: I varies between 1.2 and 1.35 eV, II and III remain constant near 1.45 and 1.8 eV, respectively. Transition I is identified with that which had been previously observed in absorption measurements, and shows the same characteristic ``red shift'' associated with magnetic ordering as the temperature is lowered. Transitions I and II are superimposed near room temperature, and become separated only below 200°K, after I had shifted to lower energies. Transitions II and III are relatively temperature insensitive. The relative photoresponses associated with transitions I and II remain nearly unchanged over a temperature range in which the total photoresponse changes by orders‐of‐magnitude. This points to the likelihood that the carriers excited by these two transitions move in the same final state. Transition III corresponds to a high‐lying one which had been previously inferred from magneto‐optical measurements.