Abstract
The sulfides galena, chalcopyrite, and pyrite are semiconductors whose electrical resistivity and type are controlled by deviations from stoichiometry and impurity content, and hence by their geochemical environment. We measured electrical resistivity, type, and the impurity content (emission spectrograph and microprobe) on small volumes of sample. Our results, together with those obtained from a comprehensive literature analysis, are used to construct histograms of the natural variability in carrier density and resistivity.
Sulfur deficiency is the dominant defect in chalcopyrite and hence almost all natural samples are n-type. It appears that the copper/iron ratio is also important electrically, the copper-rich samples being the more resistive.
Important donor defects in galena (n-type samples) are antimony and bismuth impurities, and sulfur vacancies; acceptor defects (p-type samples) include silver impurities and lead vacancies. P-type samples appear to be restricted to ‘Mississippi Valley’ and argentiferous deposits.
In pyrite, electrically active impurities include cobalt, nickel, and copper as donors, and arsenic as an acceptor. Deviations from stoichiometry, in the same sense as galena, may be important. Pyrites from sedimentary and epithermal deposits are usually p-type if cupriferous sulfides are not present. Samples from hypothermal deposits are usually n-type if there are no arsenic minerals in the assemblage.