Growth and humidity-dependent electrical properties of bulk-like MoS2 thin films on Si

Bulk-like molybdenum disulfide (MoS2) thin films were deposited on Si substrates using a dc magnetron sputtering technique and n-MoS2/p-Si junctions were fabricated at room temperature (RT) and 400 °C, respectively. The typical oscillating modes of E12g and A1g were shown in the Raman spectra of the as-grown MoS2 films. Atomic force microscopy illustrated that the surfaces of the films were composed of dense nanoscale grains and scanning electron microscopy revealed the existence of large quantities of pores in the surface. The current–voltage curves of the junctions showed obvious rectifying characteristics due to the energy-band bending near the interface of MoS2/Si. The fabricated junctions exhibited humidity-dependent electrical properties. Compared with the one with the MoS2 film deposited at RT, the junction fabricated at 400 °C showed much more obvious sensing properties to humid gas. In particular, the sensitivity of the device could be tuned by external electrical fields. In the forward voltage range, the currents increased significantly after the junction was exposed to humid conditions. The response increased with increasing voltage and reached a saturated value after V = 1.9 V. The sensing performance featured high sensitivity, fast response and recovery. The junction current in the reverse voltage range decreased under the humid condition. This was contrary to that in the forward voltage range. We also studied the dependence of the sensing response on humidity levels. An almost linear correlation was obtained in the measured range of humidity levels. The sensing mechanisms of the MoS2/Si heterojunction were proposed.