Pure CuInS2 Research Articles

Photoluminescence Studies of CuInS2-CuInSe2 Alloy Crystals

Photoluminescence spectra are presented for single crystals of CuInS2, CuInSe2 and CuInS2ySe2-2y alloys. The PL spectrum of stoichiometric CuInSe2 is dominated by free exciton emission of 9 meV FWHM at 1.03 eV, but structure at 090, 0.94 and 0.97 eV is observed due to transitions involving residual native defect states. For pure CuInS2 broad deep luminescence bands are obtained that involve several deep native defect states, e.g. donors at 45 and 160 meV below the CBE and acceptors at 85 meV above the VBE. These defects persist in S-rich CuInS2/CuInSe2 alloys, but excitonic emission is observed, in addition to the deep luminescence. Surprisingly CuInS2ySe2-2y crystals at y ≳ l are totally dominated by free exciton emission. This result shows that an increase of at least 20% over the bandgap of CuInSe2 and excellent crystal quality can be achieved by partial substitution of Se by S.