Enhancing Optoelectronic Performance of MoTe₂/MoS₂ van der Waals Heterostructure Photodiode by Air Annealing

Two-dimensional van der Waals heterostructures of transition-metal dichalcogenides (TMDCs) are of significant interest for nano- and optoelectronic applications including photodetection. While MoTe2/MoS2 heterojunction photodetectors have been demonstrated, their performance─particularly responsivity and response time─remains limited. To address this, we fabricated a semivertical MoTe2/MoS2 heterostructure photodiode. Air annealing at 200 °C induces p-type doping in MoTe2 via oxidation, converting the junction from the n-n to p-n type and enhancing the built-in electric field for efficient carrier separation. Concurrently, annealing reduces the metal–semiconductor Schottky barrier, lowering contact resistance. These modifications significantly improve the photoresponse across visible to near-infrared wavelengths. The optimized device exhibits exceptional characteristics: a low dark current (2.6 × 10–11 A), a high switching ratio (∼1 × 104), and fast rise/fall times (51/67 μs at 0 V; 8.20/8.21 μs at 1 V). Under 1064 nm illumination in photovoltaic mode, it achieves a specific detectivity near 2.2 × 1011 Jones, a responsivity of 0.19 A/W, and an EQE of 22%. This work systematically demonstrates air annealing as an effective strategy for enhancing MoTe2/MoS2 photodiodes, facilitating their development for large-scale integration.