Violet phosphorus (VP), an allotrope of phosphorus, is a two-dimensional van der Waals layered semiconducting material with a tunable band gap ranging from 1.4 to 2.0 eV. Despite its potential for optoelectronic applications, the scalable synthesis of phase-pure, high-quality VP crystals remains a major challenge due to competition from other phosphorus allotropes during growth. Here, we report a phase-selective synthesis strategy based on a Sn–Bi binary metal flux, enabling the growth of VP single crystals with lateral dimensions of up to 5 mm. Our approach leverages the presence of Sn in Bi flux to suppress the nucleation of undesired allotropes, thereby promoting the selective formation of VP. The VP crystals exhibit exceptional quality, as confirmed by a narrow full width at half-maximum of 0.098° for the (004) plane in X-ray diffraction. Furthermore, the VP-based phototransistor demonstrates an ultrahigh detectivity of ∼1.68 × 1015 cm Hz0.5 W–1 under a 458 nm (2.70 eV) laser irradiation, with a fast response time of 1.05 ms. These results highlight the optoelectronic potential of VP and the importance of phase purity and crystallinity in achieving a high-performance device, enabled by our phase-selective synthesis strategy that effectively suppresses the nucleation of competing allotropes.
