Intercalation-induced ohmic contact and exceptionally low contact resistance in blue phosphorene heterojunctions.

The achievement of low-resistance ohmic contacts in 2D semiconductors is hindered by Fermi-level pinning. Here, we propose an alkali-metal (Li and Na) intercalation strategy to suppress contact barriers in blue phosphorene heterojunctions. Substantial charge transfer (0.60e from Li and 0.44e from Na) induces a semiconductor-to-metal transition, forming high-quality n-type ohmic contacts. The contact resistances of four device configurations approach the quantum limit (∼15.9 Ω µm), with the lowest value of 16.3 Ω µm achieved for the Na-intercalated device along the armchair direction, outperforming most reported 2D semiconductor contacts. This intercalation strategy provides a promising route towards barrier-free, ultra-low-resistance contacts in 2D transistors.