Self-Powered High-Performance WS₂ Photodetector via a Monolithic p–i–n Homojunction

Lateral homojunction photodetectors (PDs) offer high responsivity and fast response, yet challenges in tailoring carrier concentrations in two-dimensional transition-metal dichalcogenides (TMDs) have limited their implementation. Here, we demonstrate a high-performance self-powered monolithic lateral p–i–n homojunction PD using multilayer WS2. To our knowledge, this study is the first report of achieving tunable, multilevel compensation doping via WOX formation using only time-controlled and region-selective ultraviolet (UV)/ozone oxidation. The oxidation process transforms WS2 through distinct phases: initial WOX (2 < X < 3) formation with thickness growth (0–90 min), increased WO3 ratio without thickness change (90–120 min), and self-limited saturation (>120 min). Photocurrent mapping confirms the formation of a lateral p–i–n homojunction, achieving a responsivity of 471 mA/W at 530 nm, a rejection ratio of 200, and response times of ∼4.5 ms under photovoltaic-mode operation. This study enables precise control of free carrier concentrations in TMDs, paving the way to versatile monolithic homojunction optoelectronic devices.