Influence of electrochemical activation and surface orientation on the photoresponse of single crystalline pyrite/electrolyte and pyrite/metal junctions

The current/voltage curves of crystalline (100)- and (111)-oriented surfaces of n-pyrite/electrolyte and n-pyrite/Pt junctions in darkness and under illumination are strongly influenced by cathodic hydrogen evolution before junction formation. Higher dark current and lower photocurrent on n-pyrite (111)-oriented surfaces in comparison to (100)-oriented surfaces were obtained. The junction properties of the untreated surfaces change from a metal-like behaviour to a rectifying one. During electrochemical treatment different etching patterns develop according to the exposed surface orientation. In the case of (111)-oriented crystals these patterns are identified as new (100)-surfaces. Quantum yields of ca. 0.7 at photon energies of 1.4 eV and almost similar photocurrent action spectra are obtained on n-pyrite/electrolyte and n-pyrite/metal junctions. The energetical position of the subbandgap response at 0.68 eV is not changed during etching. The increase of the quantum yield for photon energies higher than 1.4 eV on both types of junction points towards a reduction of surface recombination centers on etched samples. EBIC analysis on previously etched n-pyrite in contact to vacuum deposited platinum films of 120 to 1000 A thickness (Schottky barriers) indicate that the charge carrier collection efficiency is higher on etched areas. The role of surface recombination processes for photocurrent generation is demonstrated and discussed.