Sensitive photodetection in a violet phosphorus tunnel junction

Two-dimensional violet phosphorus (VP), a semiconductor with a tunable bandgap and anisotropic crystal structure, has demonstrated significant potential for photodetector applications due to its extremely high light on/off ratio and anisotropic light detectivity. Nonetheless, its performance is hindered by substantial intrinsic resistance, resulting in low photoresponsivity. In this work, we introduce a gate-tunable vertical tunnel junction device that employs thin-film violet phosphorus as the tunneling barrier and graphene as the electrode. This configuration shortens the transport path for photo-excited charge carriers in violet phosphorus, leading to a decreased recombination rate and a marked enhancement in photoresponsivity. Our device maintains a light-to-dark current ratio exceeding 2 × 10⁵ and achieves an optimized photoresponsivity of 0.58 A/W at the 532 nm excitation by fine-tuning the bias and gate voltages. Furthermore, we detect a noticeable photocurrent signal even when the excitation photon energy falls below the bandgap of violet phosphorus. The infrared photoresponse diverges from the visible-light response in both temperature and polarization dependencies, indicating two distinct underlying mechanisms for photocurrent generation in these spectral ranges. This multi-mechanism detection strategy expands the wavelength capabilities for violet phosphorus-based photodetectors, opening new avenues, to the best of our knowledge, for advanced optoelectronic devices.