Absorption Edge Studies of CuGaS2 Single Crystal

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Abstract
The transmission and reflection spectra have been measured in CuGaS2 single crystals near the absorption edge in the temperature range 77–293 K. The absorption spectra for E⊥ Z calculated by assuming that the absorption band of the A-exciton is superposed on the absorption tail expressed as Urbach's rule fits the experimental spectra fairly well in that temperature range. Thus, the temperature dependence of the A-exciton energy (E 01) becomes clear. The reflectivity maximum coincides with E 01 only at low temperatures (< 100 K). Other parameters such as the damping constant, steepness factor and oscillator strength for the Γ5 exciton are also discussed.