High‐Gain MoS ₂ Differential PNP Bipolar Junction Transistors for Dynamic Amplification via Contact‐Barrier Tuning

ABSTRACT

Silicon‐based bipolar junction transistors (BJTs) have been the workhorse of high‐frequency analog circuits, yet their scaling is fundamentally constrained by base‐width reduction and heavy‐doping‐induced carrier scattering. Although two‐dimensional (2D) semiconductors offer atomically thin bodies that are attractive for vertically scaled bipolar devices, realizing high current gain PNP BJT remains particularly challenging because stable, damage‐free p‐type doping and efficient hole‐injection schemes are difficult to achieve. Here, we demonstrate a dopant‐free PNP BJT based on multilayer MoS ₂ , in which the transistor polarity is defined by metal‐semiconductor contact engineering rather than chemical doping or van der Waals heterostacking. High‐work‐function metal Pt/MoS ₂ Schottky contacts act as bias‐tunable emitter and collector junctions for hole injection and collection, whereas a low‐work‐function metal Ag/MoS ₂ Ohmic contact serves as the base electrode. Benefiting from an ultrashort vertical base region and asymmetric effective Pt/MoS ₂ Schottky barriers, the device achieves a near‐1 common‐base current gain of α ≈ 0.99 and a high common‐emitter current gain of β ≈ 254. Furthermore, dynamic single‐transistor and differential‐amplifier confirm signal amplification with reduced waveform distortion, supporting the proof‐of‐concept dynamic amplification capability of the PNP operation. This work establishes contact‐induced band engineering as a compact strategy for complementary bipolar devices in integrated 2D analog electronics.