Robust n-type conduction with high on/off ratios in violet phosphorus field-effect transistors

Elemental phosphorus exhibits a rich polymorphism, and violet phosphorus (VP) has recently emerged as a layered semiconductor of interest for electronic and optoelectronic applications. However, its intrinsic charge-transport behavior has remained elusive, largely obscured by suboptimal device integration, low interface quality, and environmental degradation. Here, we report the fabrication and systematic characterization of multi-gate field-effect transistors based on high-quality VP crystals. To preserve the pristine nature of the channel, we employ a van der Waals (vdW) heterostructure architecture featuring full hexagonal boron nitride encapsulation and high-quality electrical contacts using either pre-patterned bottom electrodes or graphite contacts. Our devices exhibit robust n-type conduction with ohmic-like contact behavior, achieving I_on/I_off current ratios approaching 10⁷ and long-term ambient stability. Notably, the n-type characteristics persist independent of the contact metal work function. Comprehensive dual-gate modulation and temperature-dependent analyses confirm clear unipolar n-type behavior of the VP channel. These findings clarify the inherent transport nature of VP and underscore the critical role of interface engineering in unlocking its full potential for advanced multifunctional electronic and optoelectronic devices.