Photoluminescence Study of Defect Levels in CuInS2 Thin Films Grown by Sulfurization Using Ditertiarybutylsulfide

Abstract

The defect-related photoluminescence (PL) levels of CuInS2 thin films prepared by sulfurization using ditertiarybutylsulfide [(t-C4H9)2S: DTBS] have been investigated. The PL spectra exhibit three low-energy peaks at 1.37, 1.34, and 1.24 eV. On the basis of these PL spectra observed at different excitation intensities, the emissions are attributed to donor–acceptor pair transitions. The ionization energies of donors in CuInS2 thin films are determined to be 125, 150, and 280 meV, which are, respectively, due to indium atom-occupied copper vacancies (InCu), sulfur vacancies (VS), and sulfur atom-occupied copper vacancies (SCu); whereas that of the acceptor is determined to be 100 meV and has been reported to the copper vacancy (VCu). Using these data, a band diagram for the defect levels of CuInS2 thin films prepared by sulfurization is proposed.