Temperature dependence of excitonic emission in CuInSe₂

Abstract

Radiative recombination processes in CuInSe2 (CIS) single crystals grown by the, vertical Bridgman technique were studied using photoluminescence (PL) and reflectance (RF) spectroscopies at temperatures from 4.2 to 60 K, and excitation intensity from 0.6 to 30 W/cm(2). Study of the quenching parameters of the A and B freeo and first three bound-excitons (M1, M2 and M3) in high-quality CuInSe2 single crystal leads to estimates for the binding energy of the A (7.7 meV) and B (7.9 meV) free excitons as well as dissociation energies for the M1, M2 and M3 bound-excitons

Photoluminescence characterization of Cu2GeS3 bulk crystals

“…Figure shows the temperature dependence of the integrated intensities of the resolved spectra for FX and BX. The measured data for BX were fitted based on the following expression : where I ( T ) is the integrated PL intensity, C is a pre‐exponential factor, T is temperature, and E a is the thermal activation energy for bound‐exciton luminescence. The thermal activation energy of BX was estimated to be 9 meV.…”

Excited states of the free excitons in CuInSe2 single crystals

“…Previous experimental attempts to determine the free exciton binding energies E b in CuInSe 2 have been carried out by analyzing either the temperature quenching of the excitonic photoluminescence ͑PL͒ emission intensity 7,9 or diamagnetic shifts under the influence of magnetic fields. 10 The quenching characteristics of the A and B excitons are rather complex due to the small energy splitting and proximity of shallow bound excitons and thus values of E b determined by this method cannot be considered as reliable.…”

“…More details on the experimental set ups can be found elsewhere. 9,10,12 The near band gap region of the PL and RF spectra taken in CuInSe 2 at 4.2K and 6K, respectively, using nonpolarized light, are shown in Figs. 1͑a͒ and 1͑b͒, respectively.…”

“…8 In addition to the free exciton lines the spectrum shows several well resolved lines M1-M7 which have been previously attributed to bound excitons and their excited states. [7][8][9] The chalcopyrite structure of CuInSe 2 can be derived from the sphalerite zinc blende structure of ZnSe by the ordered replacement of Zn either with Cu or In. These two nonequivalent replacements result in two different lengths for the chemical bonds Cu-Se and In-Se creating a tetragonal distortion 18 splitting the triply degenerated valence band at the ⌫ point of the Brillouin zone in ZnSe into the three sub-bands A, B, and C. In terms of the quasicubic model 20 this splitting can be described as the simultaneous influence of the noncubic crystal-field and spin-orbit interactions, which in CuInSe 2 determine the spectral splitting of the A-B and B-C bands, respectively.…”

Excitation power and temperature dependence of excitons in CuInSe2

“…7,[19][20][21] Temperature and excitation power dependent PL measurements of such excitonic features would provide important information about the free excitons and on the nature of defects associated with the bound excitons. 22,23 Yakushev et al 24 reported an analysis of the temperature and excitation power dependence of the free excitons associated with the A and B valence sub-bands, and of the first three bound excitons. Although the quality of the CuInSe 2 in that investigation was high enough to resolve the A and B free excitons, the resolution of the different bound exciton lines was limited.…”