SPECTROSCOPIC ELLIPSOMETRIC OBSERVATION OF CHARGE-TRANSFER TRANSITIONS IN ZN1-XCOXSE FILMS

We report the observation by spectroscopic ellipsometry of a charge-tr ansfer-type p-to-d transition in Zn1-xCoxSe films grown on GaAs substr ates with 0 less than or equal to x < 0.1. For x > 0.04 samples, we ob served an absorption feature near 4.3 eV within the E-0 + Delta(0) - E -1 band gap region. This new structure appears to have the characteris tics of a charge-transfer-type p-to-d transition. A many body approach was used to interpret this feature as a local charge-transfer transit ion. Another observation, the decrease of the interference pattern abo ve 2.2 eV, was explained as a nonlocal charge-transfer transition. A c alculation using a multilayer model (air/Zn1-xCoxSe/GaAs) showed the s ame behavior as that of the measured spectrum.