Electrical characterization and ammonia sensing properties of MoS2/Si p-n junction

Molybdenum disulfide (MoS2) thin films are grown on p-type Si substrates by dc magnetron sputtering technique and MoS2/Si p-n junctions are fabricated. The typical oscillating modes of E12g and A1g are shown in the Raman spectrum of the MoS2 film. Atomic force microscopy illustrates that the surface of the deposited MoS2 film is composed of dense nano-level grains. The electrical characteristics of the junction are investigated. The current-voltage curves of the p-n junction show good rectifying characteristics and change dramatically with temperature. The fabricated junction exhibits obvious sensing properties to ammonia gas (NH3) at room temperature. Especially, the sensing behaviors can be tuned by external electrical fields. In the forward voltage range, the currents increase significantly after the junction is exposed to NH3 and the response increases with increasing voltage. The sensing performance is featured by a high sensitivity (∼769.2% toward 9000 ppm and ∼19.1% toward 200 ppm), and fast response and recovery (∼5.0 s). The response in reverse voltage range is contrary to that in forward voltage range and decreases with increasing the reverse voltage. We also study the dependence of the sensing response on NH3 concentration. An almost linear correlation is obtained in the measured range of NH3 concentration. The sensing mechanisms of the MoS2/Si p-n junction are proposed.