Pressure-Driven Reversible Switching between n- and p-Type Conduction in Chalcopyrite CuFeS2

Temperature-dependent switching between p- and n-type conduction is a newly observed phenomenon in very few Ag-based semiconductors, which may promote fascinating applications in modern electronics. Pressure, as an efficient external stimulus that has driven collective phenomena such as spin-crossover and Mott transition, is also expected to initialize a conduction-type switching in transition metal-based semiconductors. Herein, we report the observation of a pressure-driven dramatic switching between p- and n-type conduction in chalcopyrite CuFeS2 associated with a structural phase transition. Under compression around 8 GPa, CuFeS2 undergoes a phase transition with symmetry breakdown from space group I-42d to space group I-4 accompanying with a remarkable volume shrinkage of the FeS4 tetrahedra. A high-to-low spin crossover of Fe2+ (S = 2 to S = 0) is manifested along with this phase transition. Instead of pressure-driven metallization, a surprising semiconductor-to-semiconductor transition is observed associated with the structural and electronic transformations. Significantly, both photocurrent and Hall coefficient measurements confirm that CuFeS2 undergoes a reversible pressure-driven p-n conduction type switching accompanying with the structural phase transition. The absence of cationic charge transfer between copper and iron during the phase transition is confirmed by both X-ray absorption near-edge spectra (Cu/Fe, K-edge) and total-fluorescence-yield X-ray absorption spectra (Fe, K-edge) results, and the valence distribution maintains Cu2+Fe2+S2 in the high-pressure phase. The observation of an abrupt pressure-driven p-n conduction type switching in a transition metal-based semiconductor paves the way to novel pressure-responsive switching devices.