Emerging avalanche field-effect transistors based on two-dimensional semiconductor materials and their sensory applications

Two-dimensional (2D) layered semiconductors offer unique electronic and optoelectronic properties (high carrier mobility, tunable band gaps, atomic thickness) that are advantageous for avalanche field-effect transistors (FETs) and sensors. This review surveys avalanche phenomena (impact ionization, breakdown field, carrier multiplication) in 2D-material FETs and photodetectors, highlights device architectures (e.g., MoS2, WSe2, heterostructures such as WSe2/MoS2, WSe2/WS2), and summarizes figures of merit (responsivity, detectivity, EQE, gain) relevant to photo-, bio- and gas-sensing. We discuss thickness/channel-length effects, contact barriers, temperature dependence, and approaches to reduce breakdown voltage, as well as opportunities and challenges toward practical, low-bias, high-gain avalanche devices for sensing and imaging applications.