Photoreflectance study of AgGaTe2 single crystals

The optical properties of ternary chalcopyrite AgGaTe2 were studied by photoreflectance spectorscopy (PR). Due to the optimal direct energy gap and high absorption coefficient AgGaTe2 is a promising material for solar energy conversion. Single crystals used in this work were grown by the vertical Bridgman technique. The PR temperature dependent spectra were measured in the range of 25–300 K. At room temperature two energy gaps in AgGaTe2 were detected: and , with temperature coefficients /dT=−2.1×10−4 eV/K and /dT=−3.4×10−4 eV/K. At low temperature (T=25 K) these bandgap energies were and . Temperature dependence of bandgap energies is maximum at about T=90 K