High-Performance Two-Dimensional van der Waals Enabled Bipolar Junction Transistors with Current Gain Exceeding 103.

Two-dimensional (2D) van der Waals (vdW) bipolar junction transistors (BJTs) have emerged as promising building blocks for next-generation electronic devices, owing to their atomically sharp interfaces and unique electronic properties. Here, we demonstrated a MoS2/WSe2/MoS2 vdW npn BJT assembled by mechanical exfoliation and a deterministic transfer. The device exhibited an excellent bipolar operation under both common-base and common-emitter configurations. More importantly, a common-emitter current gain exceeding 103 was achieved, representing one of the highest experimentally reported values for 2D vdW heterostructure BJTs. A common-base current transfer ratio approaching unity confirms efficient minority carrier transport across the ultrathin WSe2 base. In addition, TCAD simulations reproduce the experimental characteristics and reveal the underlying transport mechanism. The simulations showed that reducing the base thickness effectively enhanced the current gain by suppressing carrier recombination, whereas excessive thinning activated band-to-band tunneling, resulting in a reverse base current and limiting further gain improvement. This work demonstrates a high-performance vdW BJT and provides important design guidelines for optimizing bipolar transport in atomically thin semiconductors.