Donghun Lee
Two-dimensional transition metal dichalcogenides are being studied as channel materials for beyond-silicon electronics because their atomic-scale thickness enables strong electrostatic control. Among these materials, tungsten diselenide (WSe2) is particularly attractive because it exhibits ambipolar transport. Despite this advantage, practical WSe2 transistors remain constrained by Fermi-level pinning at metal contacts, contact-dominated carrier injection, and defect-induced variability, making controlled doping a central issue. This review examines doping strategies developed for WSe2, focusing on methods compatible with atomically thin van der Waals semiconductors. The discussion covers surface charge-transfer doping by molecular adsorbates, Lewis acids, and alkali metals, as well as defect-mediated chemisorption, self-limiting oxide interfacial layers, and in situ vacancy engineering during growth. Particular attention is given to the thermodynamic mechanisms of charge transfer, the distinction between contact-selective and channel-selective doping, and the trade-offs between degenerate and non-degenerate doping. The effects of doping are also discussed, including contact-resistance reduction through Schottky-barrier narrowing, threshold-voltage control, apparent mobility enhancement through impurity screening and defect passivation, and thermal and temporal stability. The review further summarizes how controlled doping has enabled complementary metal-oxide-semiconductor logic circuits and identifies the remaining challenges in air stability, selective-area patterning, scalable synthesis, and low-temperature integration for monolithic three-dimensional electronic devices.