Electrical,optical and photoelectrochemical properties of natural enargite,Cu3AsS4

The semiconducting properties of natural samples of enargite, a copper and arsenic suphide (Cu₃AsS₄), have been studied. They have been found to be p-type semiconductors with a resistivity of about 7 Ω cm, a doping level of about 10¹⁷ cm^?3 and a mobility of 9 cm²V^?1 s^?1. The variation of the resistivity as a function of temperature allows to determine an activation energy of 0.11 eV. Two optical transitions have been determined, an indirect one at 1.19 eV and a direct one at 1.44 eV. The samples, mounted as working electrodes in a photoelectrochemical set-up, are photosensitive and behave as p-type photocathodes. The two transitions are found again from the analysis of photocurrent spectra. The direct band gap value is close to the ideal value required for photovoltaic applications. However the quantum efficiencies obtained here are still low.