Nickel-incorporated FeS2 single crystals with various Ni compositions of Fe0.99S2:Ni-0.01, Fe0.98S2:Ni-0.02, Fe0.96S2:Ni-0.04, and Fe0.9S2:Ni-0.1 were grown by chemical vapor transport (CVT) method using ICl3 as a transport agent. Physical properties of the Ni-incorporated FeS2 single crystals were characterized using X-ray diffraction, Raman spectroscopy, electrical conductivity, and photoconductivity (PC) measurements. By means of the analyses of the X-ray diffraction patterns, the whole series of Ni-doped FeS2 single crystals were determined to be single-phase and isostructural. Raman spectroscopy of the Ni-doped FeS2 crystals was carried out at room temperature. Raman resonant peaks of the Ni-doped FeS2 crystals demonstrate an energy red-shift behavior with respect to the increase of the dopant densities. Conductivity measurements show the resistivity of the Ni-doped FeS2 decreased as the doping concentration of Ni is increased. Nickel is an n-type dopant, which behaves like a donor level existed near the conduction band edge of the synthetic FeS2. On the other hand, dopant effect of nickel on the synthetic FeS2 also destroys the photoconductive sensitivity in the photoconductivity measurements. (C) 2004 Elsevier B.V. All rights reserved.