Photoreflectance study of AgGaTe 2 single crystals

Abstract

The optical properties of ternary chalcopyrite AgGaTe 2 were studied by photoreflectance spectorscopy (PR). Due to the optimal direct energy gap and high absorption coefficient AgGaTe 2 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 AgGaTe 2 were detected: E g A = 1 . 32 0 eV and E g B = 1 . 425 eV , with temperature coefficients d E g A / dT=−2.1×10 −4 eV/K and d E g B / dT=−3.4×10 −4 eV/K. At low temperature ( T=25 K) these bandgap energies were E g A = 1 . 355 eV and E g B = 1 . 466 eV . Temperature dependence of bandgap energies is maximum at about T=90 K.