A single material can now efficiently inject charge into two different types of atomically thin transistors, a breakthrough that could accelerate the development of next-generation AI chips. Researchers at The Korea Advanced Institute of Science and Technology (KAIST) have demonstrated that tin diselenide (SnSe2) works as a universal charge injector for both n-type and p-type semiconductor channels, eliminating the need for separately optimized electrodes in each transistor type.
The finding addresses a persistent bottleneck in two-dimensional semiconductors, which are less than a nanometer thick and can be stacked vertically to fit more transistors into the same physical space. Injecting charge efficiently into these ultrathin materials has been difficult because conventional metal electrodes can damage their delicate atomic structure and create barriers that obstruct electrical flow.
SnSe2 solves this problem through weak interatomic attractions called van der Waals forces, which preserve the semiconductor channel and create a clean interface. Depending on which semiconductor it contacts, SnSe2 adapts its charge-injection pathway through different quantum tunneling mechanisms, without requiring any change to the material itself.
How One Material Serves Two Transistor Types
When paired with p-type tungsten diselenide (WSe2), SnSe2 forms a broken-gap band alignment that enables efficient band-to-band tunneling. Charge carriers pass through an energy barrier quantum mechanically rather than acquiring enough energy to travel over it.
When combined with n-type molybdenum disulfide (MoS2), the same SnSe2 injector creates a different junction. An applied gate field reshapes and narrows the electron-injection barrier, allowing electrons to tunnel through it. In essence, one material automatically adapts to two different transistor polarities through distinct tunneling routes.
Performance Gains at Scale
The performance improvements were substantial. In p-type WSe2 transistors, the SnSe2 injector increased maximum drive current by more than 1,000 times compared with conventional nickel electrodes. Drive current measures the maximum current a transistor can deliver when switched on.
In n-type MoS₂ transistors, SnSe2 enabled steep switching and an on/off current ratio exceeding 1 billion. This means the device conducts current effectively in its on state while strongly suppressing current in its off state. The research team also fabricated a CMOS inverter, a basic building block of digital circuits that combines both transistor types, and confirmed it operated reliably in response to repeated input signals.
Scaling Toward Stacked Three-Dimensional Chips
The key contribution is demonstrating that a single material can efficiently supply charge to both types of ultrathin semiconductors. This moves beyond the conventional approach of using separate electrodes for n-type and p-type devices, simplifying fabrication and reducing the complexity of multilayer designs.
With further advances in direct growth, large-area fabrication and device integration, two-dimensional semiconductors could eventually be stacked in multiple layers to form three-dimensional chips. Such architectures could accommodate more transistors within the same footprint, perform more functions, and consume less power.
Professor Joonki Suh from KAIST stated that “efficient charge injection, one of the most challenging bottlenecks in monolayer two-dimensional semiconductors, can be addressed using a single material platform.” With continued progress in direct growth and large-area processing, this approach could accelerate the practical implementation of low-power two-dimensional CMOS integrated circuits for AI processors and ultra-low-power electronic devices.
The study was led by KAIST Ph.D. candidate Hanbin Cho, with Professor Kyungmin Ko from Yonsei University and Professor Suh serving as co-corresponding authors. The research involved collaboration with Yonsei University, the Beijing Computational Science Research Center, the Korea Institute of Science and Technology (KIST), Hanyang University, the Ulsan National Institute of Science and Technology (UNIST), and Samsung Electronics.
