Near-infrared optical analysis of CuInSe2(1±x) crystals using transmission, photoacoustic and transmission-photoacoustic spectroscopies

Abstract

We report on the near infrared optical absorption properties of CuInSe2(1±x) single crystals in which small deviations (x) are introduced into the valence stoichiometry prior to the crystal growth using three spectroscopic techniques: transmission, photoacoustic and transmission-photoacoustic. Monocrystalline samples were cut from ingots grown using the Bridgman technique with the compositions: CuInSe2, CuInSe1.787, CuInSe2.084 and CuInSe2.212. The phases and crystallographic structures were checked from their corresponding powders using X-ray diffraction. The optical properties were measured in photon energy range 0.7 to 1.2 eV. A comparison between the extracted absorption spectral distributions from different measurement methods is presented. Resolved peaks at photon energies higher than the compound bandgap close to the conduction/valence bands due to inter-bands transitions are detected from photoacoustic measurements. Also discussed are the defect levels observed in the spectra tail following the alloy starting composition change. It is shown that the sensitivity of photoacoustic operational modes to detect changes due to modification in samples’ composition is higher than the transmission technique. Differences in spectral behavior with particular attention being given to the detected defects from different measuring operational modes are discussed.