ELECTROREFLECTANCE OF CUINSE2 SINGLE-CRYSTALS

Electrolyte electroreflectance (ER) measurements have been carried out at room temperature (297 K) on a series of bulk single crystals of Cu InSe2 prepared by the normal freezing method with various Cu/In ratios . The Cu-rich crystals exhibited sharp ER peaks and the AB-transition energy is 1.026 eV, while In-rich crystals exhibited broader ER peaks and smaller AB-transition energies (1.00-1.02 eV) than those of the Cu -rich ones. The spin-orbit splitting of the uppermost valence band is 0.236 eV. The effect of the Cu/In ratio on the ER spectra is discussed in terms of the Urbach energy determined by optical absorption measur ement, and the bandgap energy of the stoichiometric CuInSe2 crystal is discussed.