Anomalous Sub‐Band Gap Emission at Room Temperature in Mixed‐Dimensional WS 2 /Cu 2 O Heterostructures

ABSTRACT Practical implementation of two‐dimensional (2D) transition‐metal dichalcogenides (TMDCs) in novel optoelectronics requires a fundamental understanding of carrier dynamics and interfacial states at 2D/3D heterostructures. Herein, a mixed‐dimensional p‐n junction based on monolayer tungsten disulfide () and cuprous oxide () is investigated. An anomalous emission (AE) at 1.66 eV is identified at room temperature, which is in the same spectral range as oxygen‐related defect luminescence, but is enhanced at the heterointerface under 457 nm excitation. While this sub‐bandgap feature resembles the spectral signature of an interlayer exciton (ILX), its combined excitation‐wavelength, power, temperature, and bias dependence suggests that the emission is predominantly defect‐mediated and modified by the / interface. External modulation of the AE intensity is demonstrated via vertical bias, yielding an approximately 45% maximum‐to‐minimum modulation of the normalized AE/ PL area ratio over the applied bias range from V to V at 93 K. This modulation is asymmetric, showing a correlation between AE quenching and photocurrent generation under reverse bias. The spectral response peaks near the open‐circuit condition, marking a regime of efficient carrier accumulation and interfacial trapping. These findings identify / as a model hybrid interface for probing electrically tunable defect‐mediated recombination in mixed‐dimensional heterostructures.