Effect of excitation intensity and temperature on photoluminescence of thin films of the Cu$_2$ZnSnSe$_4$ compound

The results of the study of the phase composition, structural characteristics and photoluminescence (PL) of thin films of the direct-gap compound Cu$_2$ZnSnSe$_4$ (CZTSe) with the kesterite structure are presented. X-ray spectral local microanalysis with energy dispersion showed that the ratio of elements in the CZTSe compound is: [Cu]/[Zn +Sn] $\sim$ 0.75 and [Zn]/[Sn] $\sim$ 1.17. Using X-ray diffraction analysis, the unit cell parameters of the CZTSe compound thin films were determined to be: $a\sim$ 5.692 $\mathring{\mathrm{A}}$ and $c\sim$ 11.33 $\mathring{\mathrm{A}}$. Based on the measurement data of PL spectra and PL excitation spectra at temperatures in the range of 6–300 K, the band gap width $E_g\sim$ 1.052 eV of CZTSe thin films, the position of the energy levels of structure defects in the band gap were determined, and the mechanisms of radiative recombination of nonequilibrium charge carriers were established. The nature of growth defects in the structure of the CZTSe compound is discussed.