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Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) such as tungsten diselenide (WSe₂) have potential for next-generation CMOS and optoelectronic devices due to their atomically thin structure and tunable electrical properties. Key challenges in 2D TMD CMOS include achieving high-performance p-type field effect transistors (FETs), as well as seamless integration of balanced n- and p-type devices for scalable logic circuits. Surface oxidation induces p-type doping in WSe₂ through a self-limiting tungsten oxide (WOₓ) layer, enabling efficient hole injection in WSe₂ p-FETs via surface charge transfer. We show how selective contact adjacent doping leads to strongly enhanced and exceptionally stable p-type behavior, with negligible electrical hysteresis. Additionally, by selectively removing WOₓ, we fabricate close-proximity n- and p-FETs on a single WSe₂ flake, achieving low power inverter operation. Photodiode measurements demonstrate stable on-off switching under low-power laser excitation with fast response times, low dark current, gate-controllable responsivity, and self-powered operation at zero bias. We further investigate the oxide quality and electrical properties through surface microscopy techniques. The capacitance variation reveals a distinct pn junction, with a work function difference of ~120 meV between the oxidized and pristine regions. Such oxidation treatment enables single-material pn junctions, potentially simplifying material synthesis and streamlining fabrication, attractive for scalable 2D CMOS technologies.