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) arc 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 1.20₄ and 1.21₅ eV for CuIn₃Se₅ and Cu₂In₄Se₇ crystals, respectively. This work also refers to the photoluminescence and photoreflectance spectra at 77 K.