Photoluminescence studies in CuInS2 thin films grown by sulfurization using ditertiarybutylsulfide

Abstract

The defect-related levels of CuInS2 thin films prepared by sulfurization using ditertiarybutylsulfide [(t-C4H9)2S:DTBS] have been investigated by photoluminescence (PL) spectroscopy. The PL spectra exhibit four peaks at 1.43, 1.27, 1.21, and 1.17 eV. On the basis of the PL spectra observed at various excitation intensities and temperatures, the peak emissions are attributed to donor–acceptor pair transitions. The ionization energies of donors in CuInS2 thin films are determined to be 66, 330, 300, and 150 meV, and the ionization energies of acceptors are estimated to be 100, 170, and 390 meV, respectively. As a result of the different sulfurization conditions and times, the donors corresponding to these ionization energies are due to indium interstitial (Ini), indium atoms-occupied sulfur vacancies (InS), sulfur atoms-occupied copper vacancies (SCu), and sulfur vacancies (VS), and the acceptors are determined to be due to copper vacancies (VCu), sulfur interstitial (Si), and sulfur atoms-occupied indium vacancies (SIn), respectively. Using these data, a band diagram for the defect levels of CuInS2 thin films has been proposed.