Enhanced Photoresponse of WS₂ Photodetectors through Interfacial Defect Engineering Using a TiO₂ Interlayer

To develop a stable and reliable two-dimensional (2D) tungsten disulfide (WS₂)-based photodetector (PD), it is essential to address the issue of interfacial defects that are unavoidably formed at the interface between WS₂ and metal contact as such defects can markedly deteriorate photoresponse characteristics. In this work, this drawback is mitigated by adopting a facile technique for passivating a WS₂ surface with an ultrathin TiO₂ film. The TiO₂ interlayer is deposited on the 2D WS₂ surface via 20 cycles of atomic layer deposition prior to proceeding with photolithography and contact metal deposition. Advanced characterizations reveal that TiO₂/WS₂ PDs exhibit enhanced photoresponse compared to bare WS₂. Much higher photoresponsivity (∼10 times higher at 1 mW/cm²) and faster recovery (∼124 times faster at 0.1 V) are obtained from TiO₂/WS₂ PDs relative to bare WS₂ PDs. The mechanism underlying the enhanced PD performance is demonstrated. The computational density functional theory using the Heyd–Scuseria–Ernzerhof approach demonstrates the significant role of the TiO₂/WS₂ interface in facilitating the charge transfer and improving the PD performance compared to the bare WS₂ device. This approach paves the way for developing reliable and high-performance 2D WS₂-based optoelectronic devices.