Free-to-bound recombination in near stoichiometric Cu2ZnSnS4 single crystals

Cu2ZnSnS4 single crystals prepared by the chemical vapor transport technique were investigated by x- ray diffraction, chemical microprobe analysis, and Raman and photoluminescence spectroscopies. Single-crystal x-ray measurements show that Cu2ZnSnS4 crystallizes in the kesterite structure with the space group I (4) over bar and unit cell parameters a = 5.4174(2) and c = 10.7903(7) angstrom at 150 K. Photoluminescence measurements show one broad asymmetric band peaked at 1.29 eV at low temperature. Temperature and excitation intensity dependencies of the luminescence band indicate that the transition is due to a free-to-bound recombination with an activation energy of 140 meV. We attribute this activation energy to the intrinsic acceptor-type Cu-Zn antisite defect in close agreement with results from density-functional theory. It is shown that by a detailed analysis of the temperature dependence of the free-to-bound luminescence transition the majority carrier density can be deduced, which in our case is estimated at p approximate to 10(16) cm(-3).