Photoluminescence excitation spectroscopy of highly compensated CuGaSe₂

Abstract

The photoluminescence excitation spectra are presented of weakly and highly compensated CuGaSe 2 , grown under Cu-excess and under Cu-deficiency, respectively. An overlap is observed between the photoluminescence and the excitation spectrum in the Cu-poor material, indicating fluctuating potentials due to high compensation, whereas no overlap is observed in material grown under Cu-excess, indicating flat bands. The photoluminescence excitation spectra can be used as measure for the absorption spectrum in the case of flat bands, but not in the case fluctuating potentials, where different emission energies probe different depths of the fluctuations. Methods for the determination of the fluctuation amplitude from the photoluminescence and the excitation spectra are discussed.

Photoluminescence investigation of Cu 2 ZnSnS 4 thin film solar cells

“…The differences are large (250 -400 meV), indicating that rather deep defects are involved in the q-DAP transitions. In CIGS the shift between the PLE onset and PL maximum is smaller than 200 meV [18,22,23,24,25]. In figure 5b a clear decrease of the linear extrapolations of squared PLE as a function of temperature can be seen.…”

“…In figure 5a it is seen that the long wavelength side of the PLE spectra is structureless: a free exciton band is not resolved, which confirms the presence of potential fluctuations in the material. The increase of the excitation spectrum intensity at the long wavelength side is related to the optical absorption spectrum but not identical to it, because the efficiency of the emission is also involved [23,25]. The linear extrapolation of squared PLE (labelled as E g,PLE ) at 12 K is 1.418 ± 0.045 eV.…”

Photoluminescence and Photoluminescence Excitation Spectroscopy of Cu(In,Ga)Se2Thin Films

“…The band edge shape is typically thought to be determined by an exponentially decaying density of states that extends into the forbidden gap, the width of which has been connected to the degree of structural disorder in the crystal, including disorder that results from local composition fluctuations [19]. Such band tails are common in Cu-poor CIGS and have been measured by luminescence techniques as well as transient photocapacitance spectroscopy [6,20]. Band edge widths for the six samples in this study were directly measured by fitting PLE spectra with error functions and are shown in the last column of Table I.…”

“…PL has been performed on CIGS epitaxial layers [5][6][7], polycrystals [8] and bulk single crystals [9][10]. Only a few studies have incorporated photoluminescence excitation spectroscopy (PLE), with mixed results [6,11].…”

Optical Signatures of Impurity–Impurity Interactions in Copper Containing II–VI Alloy Semiconductors

“…Such band tails have been studied qualitatively by optical spectroscopy: mainly photoluminescence (PL) as a function of temperature and excitation power [11][12][13][14][15][16][17] , but also by PL excitation spectroscopy (PLE), which reveals the density of states in the presence of potential fluctuations 18,19 , and by time-resolved photoluminescence spectroscopy (TR-PL), which gives information about the localization and transfer of carriers between the band tail states, as was done on CZTS single crystals 16,19 : all these data have been analyzed as a function of the order/disorder degree in the quaternary structure 19,20 .…”