Atomically Thin MoS₂ Layers Selectively Grown on Mo Patterned Substrates for Field-Effect-Controlled Photosensors

Selective growth of 2D MoS 2 layers on patterned substrates is highly desired for easy fabrication of devices. Selectively grown 2D MoS 2 on Mo patterned substrates for the formation of intimate metallic contact was obtained by a Mo-CVD method in which MoO 2 from an oxidized Mo pattern and S powder are the growth precursors. Mo films were deposited by magnetron sputtering on SiO 2 (300 nm)/c-Si substrates and patterned by photolithography techniques for obtaining Mo strips and finger contact structures, with the gap between the strips and finger varied from 5 to 20 μm. The filling of the gap by selectively grown atomically thin MoS 2 plates of 1–2 monolayers (MLs) was demonstrated by scanning electron microscopy and atomic force microscopy imaging. Field effect devices for the characterization of the photosensitivity of selectively grown MoS 2 have been fabricated from finger contact structures. The dark current is drastically reduced from 10 –9 to 10 –13 –10 –14 A by varying the gate voltage from +7 to −7 V, showing the n-type semiconductor behavior of the selectively grown 2D MoS 2 . High photosensitivity of 10 5 (%) was obtained for 4.5 × 10 –4 mW/cm 2 at 650 nm wavelength illumination. The spectral responsivity reaches values of 15–25 A/W at 600 nm wavelength and shows an energy onset of 1.72–1.77 eV corresponding to about 2 ML MoS 2 . The carrier-trapping effect responsible for the slow part of the device response can be caused by structural defects and also by adsorbed molecules like in gas sensors.