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Using a MoS2 field effect transistor as an Ozone Sensor

We study the electrical properties of a MoS2 thin-film transistor (TFT), which is used as an ozone gas sensor. By using mechanical exfoliation method, we placed a MoS2 thin film on a Si substrate with a 300 nm SiO2 insulating layer. The thickness of the MoS2 thin film was identified by using Raman spectroscopy, atomic force microscope and image analysis method through the software Image J. The electrodes of the MoS2 TFT were defined by e-beam lithography. The channel length and width are both 4 um. The mobility of the MoS2 TFT in vacuum and in the environment with the ozone concentration of 30 ppb are 1.72 cm V s and 0.94 cm V s, respectively. Under different luminous intensity of blue light provided by light emitting diodes (LEDs), the variation of the drain-source current (IDS) of the MoS2 device in the ambient of different ozone concentration with a transient time of 200 s was investigated by both the DC current measurement and lock-in technique. We found that IDS is varied by 100±5 nA in the DC measurement and 50±3 nA in the lock-in measurement as the ozone concentration increases 100 ppb when the luminous intensity of blue LEDs is 20mW/cm. As the luminous intensity of excitation blue LEDs was 12 mW/cm, the change of IDS is 80±5 nA in the DC measurement and 50±3 nA in the lock-in measurement as the ozone concentration increases 100 ppb. It indicates that the MoS2 TFT is a potential ozone sensor with a sensitivity down to 100 ppb of ozone concentration.