Pressure engineering of van der Waals compound RhI3: bandgap narrowing, metallization, and remarkable enhancement of photoelectric activity

The realization of high tunability in layered van der Waals halides may create new interesting optical and op-toelectronic properties. These soft materials are particularly sensitive to external stress or pressure, suggesting a feasible route to pinpoint their structure with extraordinary behavior. However, a very sensitive pressure response usually lead to a detrimental phase transition and/or lattice distortion, making the approach of ma-terials manipulation in a continuous manner remain challenging. Here, the extremely weak interlayer coupling and high tunability of layered RhI3 crystals are observed. A pressure-driven phase transition occurs at a moderate pressure of 5 GPa, interlinking to a change of layer stack mode. Strikingly, such a phase transition does not affect the tendency of quasi-linear bandgap narrowing, and a metallization with an ultra-broad tunability of 1.3 eV redshift is observed at higher pressures. Moreover, the carrier concentration of RhI3 increases by 4 orders of magnitude at 30 GPa, and the photocurrent enhances by 5 orders of magnitude at 7.8 GPa. These findings create new opportunities for exploring, tuning, and understanding the van der Waals halides by harnessing their un-usual feature of a layered structure, which is promising for future devices based on materials-by-design that are atomically thin.

Automated summary

This study demonstrates the extremely weak interlayer coupling and high tunability of layered RhI3 crystals. A pressure-driven phase transition and an ultra-broad tunability of bandgap narrowing were observed. These findings provide new opportunities for exploring and understanding layered van der Waals halides.