Near‐edge Optical Properties of CuInSe₂ Studied by Photoacoustic Spectroscopy

Abstract

Optical absorption spectra of n-type CuInSez single crystals were evaluated by means of photoacoustic spectroscopy in the photon energy range from 0.94 to 1.02 eV. At photon energies below 0.99 eV the spectra exhibit exponential tails that are ascribed to the presence of shallow impurity states. At higher photon energies the absorption coefficients follow the relation for direct allowed optical transitions between parabolic bands. The parameters of this relation are determined and compared with previous measurements.Optische Absorptionsspektren n-leitender CuInSe,-Einkristalle wurden mit Hilfe der photoakustischen Spektroskopie im Photonenenergiebereich von 0.94 bis 1.02 eV bestimmt. Bei Photonenenergien unterhalb 0.99 eV zeigen die Absorptionsspektren exponentielle Auslaufer, die dem Vorhandensein flacher Storzellen zugeschrieben werden. Bei hoheren Photonenenergien folgen die Absorptionskoeffzienten der Beziehung fur direkte erlaubte optische Ubergange zwischen parabolischen Bandern. Die Parameter dieser Beziehung werden bestimmt und mit fruheren Messungen verglichen.

Comparative optical absorption and photoreflectance study of n‐type CuInSe2 single crystals

“…lo4 -1 . lo5 cm-' eV"' from photoacoustic spectra of single crystals (ZEGADI et al 1993). Comparing with Table 1 we see that the true values of the constant A for the fundamental edge are about two orders of magnitude higher than those found in the present study which is well beyond the error limits in the experimental determination of this parameter.…”

Photoacoustic Spectroscopy of Defect States in Etched and Air‐annealed CuInSe2 Single Crystals

“…All the photoacoustic spectra obtained in the present work were analysed in this manner. The error in the gap energies is about f0.005 eV (ZEGADI et al 1993) and in the defect energies En not larger than about kO.009 eV (YAKUSHEV et al 1994e). …”

“…A typical result for the wavelength dependence of the photoacoustic spectra of cleaved n-type conducting CuInSe, crystals is represented in Figure 1. In the wavelength range above the fundamental edge of the compound the spectra exhibit five peaks 1 to 5 that can be ascribed to either impurityto-conduction band or valence band-to-impurity transitions (ZEGADI et al 1992 h (pm I gap energy of the samples from the steeply increasing part of the normalised photoacoustic amplitude q at wavelengths A below about 1.3 pm following the procedure described by ZEGADI et al (1993). The characteristic energies of the defect-induced optical transitions were identified with the maximum positions of the corresponding structures in the photoacoustic spectra (ZEGADI et al 1992).…”