Dramatic switchable polarities in conduction type and self-driven photocurrent of BiI3 via pressure engineering

Abstract

The intentional manipulation of carrier characteristics serves as a fundamental principle underlying various energy-related and optoelectronic semiconductor technologies. However, achieving switchable and reversible control of the polarity within a single material to design optimized devices remains a significant challenge. Herein, we successfully achieved dramatic reversible p-n switching during the semiconductor‒semiconductor phase transition in BiI₃ via pressure, accompanied by a substantial improvement in their photoelectric properties. Carrier polarity flipping was monitored by measuring the photocurrent dominated by the photothermoelectric (PTE) effect in a zero-bias two-terminal device. Accompanying the p-n transition, a switch between positive and negative photocurrents was observed in BiI₃, providing a feasible method to determine the conduction type of materials via photoelectric measurements. Furthermore, the combined effects of the photoconductivity and PTE mechanism improved the photoresponse and extended the detection bandwidth to encompass the optical communication waveband (1650 nm) under an external bias. The remarkable photoelectric properties were attributed to the enhanced energy band dispersion and increased charge density of BiI₃ under pressure. These findings highlight the effective and flexible modulation of carrier properties through pressure engineering and provide a foundation for designing and implementing multifunctional logic circuits and optoelectronic devices.

Keywords: conduction-type switching; high pressure; metal halide; self-driven photocurrent.

Figure 1.

Structural evolution of BiI₃ under high pressure. (a) In situ ADXRD patterns of BiI₃ at various pressures. (b) Cell parameters and (c) unit-cell volume of BiI₃ as a function of pressure. The curves are fitted using the Birch–Murnaghan equation of state. (d) Crystal structures of BiI₃ at ambient pressure and 7.8 GPa.

Figure 2.

Photocurrent measurements of BiI₃ under high pressure. (a) Schematic of the device used for in situ high-pressure photoelectric measurements. (b) Photocurrent curves of BiI₃ under xenon light illumination at typical pressures with a 5 V bias. The light spot size greatly exceeds the area of the active device, resulting in global irradiation. (c) Pressure-dependent photocurrent and responsivity (R) of BiI₃, derived from the data in (b).

Figure 3.

Pressure-induced polarity reversal of self-driven photocurrent in BiI₃. (a and b) Photoresponse of BiI₃ under 520 nm laser illumination at position A with zero bias under typical pressures. The light spot diameter of ∼10 μm indicating localized irradiation of the sample. (c) Photocurrent distribution of BiI₃ at 24.0 GPa as the laser moves between the two electrodes. The distance between two neighboring irradiation points is ∼20 μm. (d) Photocurrent changes of BiI₃ at 24.0 GPa with varying illumination intensity, extracted from Figure S8. (e) Variation in photocurrent with pressure at illumination positions A and B. (f) Changes in photothermoelectric voltage with pressure at illumination position A. (g) Pressure-dependent Hall coefficient of BiI₃.

Figure 4.

Responsiveness to near-infrared light. (a) 2D projection of the optical absorption spectra of BiI₃ under high pressures. (b) Pressure-dependent bandgap of BiI₃. (c) Photocurrent of BiI₃ at representative pressures under 1650 nm laser illumination at position A with a 5 V bias. (d) Pressure-dependent photocurrent of BiI₃ under 980 nm, 1270 nm, 1450 nm and 1650 nm laser illumination at position A with a 5 V bias.

Figure 5.

Pressure-induced variations in the electronic properties of BiI_3. (a) Band structure and PDOS of BiI₃ in the RH phase at different pressures. (b) Band structure and PDOS of BiI₃ in the Cmcm phase at different pressures. (c) Calculated charge distribution at the VBM of BiI₃ in the RH phase. (d) Calculated charge distribution at the CBM of BiI₃ in the Cmcm phase. (e) Calculated electron and hole effective masses of BiI₃ at typical pressures.