Electroreflectance of CuInSe2, CuIn3Se5 and Cu2In4Se7

Electrolyte electroreflectance (ER) measurements have been carried out at room temperature on (i) CuInSe2 bulk single crystals grown by the normal freezing method, and on (ii) bulk of CuIn3Se5 and Cu2In4Se7 crystals grown by the traveling heater method. The ER spectra for Cu-rich CuInSe2 crystals are sharp and the AB transition energies are constant (E-AB=1.028 eV). For the In-rich crystals, ER spectra are very broad and the AB transition energies (E-AB=0.99-1.02 eV) are smaller than those of Cu-rich crystals. The bandgap energy for the stoichiometric CuInSe2 is 1.035 eV at 297 K assuming that the optical transition is the exciton transition. The ER spectra of CuIn3Se5 and Cu2In4Se7 crystals at 295 K are very broad and the bandgap energies obtained from the ER spectra are 1.20(4) and 1.21(5) eV for CuIn3Se5 and Cu2In4Se7 crystals, respectively. This work also refers to the photoluminescence and photoreflectance spectra at 77 K.