Mechanism of Low Contact Resistance in Bilayer Y-InSe/InSe Heterojunction

Two-dimensional InSe is a promising candidate for post-Moore nanoelectronics, yet its performance is hindered by high contact resistance caused by Schottky barriers and Fermi-level pinning at metal interfaces. Experimental studies demonstrate that yttrium-doped InSe (Y-InSe) undergoes a semiconductor-to-semimetal transition, enabling low-resistance ohmic contacts when employed as an electrode material. However, the mechanistic origin of this improvement remains unclear. This study systematically investigates the transport properties of three devices with Y-InSe electrodes, featuring: (i) intrinsic InSe (InSe-ND), (ii) Y-substituted InSe (InSe-YIn), and (iii) Y-intercalated InSe (InSe-Yac) as the channel materials. Our calculations reveal that InSe-Yac facilitates strong charge transfer and ionic bonding, shifting the Fermi level into the conduction band and enabling effective n-type doping. This mechanism reduces the Schottky barrier height dramatically, whereas InSe-YIn exhibits only marginal modulation. InSe-Yac achieves a low contact resistance of 9.61 × 102 Ω·μm–6 orders of magnitude lower than InSe-ND/InSe-YIn (∼108 Ω·μm). We identify Y intercalation as one of the dominant mechanisms for effectively reducing contact resistance, offering a novel design principle for 2D semiconductor junctions in post-Moore electronics: controlled intercalant engineering.