Novel semiconductive tertiary and higher order type copper-Group V transition metal chalcogenides having useful broad-band photoconductive properties are characterized by containing fewer than 100 ppm of impurities as determined by electron microprobe analysis, excluding doping agents which may be present. These materials are made e.g. by chemical vapor transport methods using the powdered chalcogenide or mixtures of stoichiometric amounts of the elements of which it is composed, with a small amount of halogen or hydrogen halide and heating the mixture in vacuum in a temperature gradient in which the highest temperature is below about 1200.degree. C. Photoconducting devices can be made e.g. by supplying electrodes to a thin film of the material upon a dielectric substrate.