1T and 2H heterophase MoS 2 for enhanced sensitivity of GaN transistor-based mercury ions sensor.

We report significantly enhanced sensitivity of AlGaN/GaN-based high electron mobility transistor (HEMT) sensor by the targeted synthesis of IT and 2H coexisting phase MoS 2 and applying the gate bias voltage. The HEMT structures on Si (111) substrates were used for the detection of Hg 2+ ions. The optimum sensitive regime in terms of V GS and V DS of the sensor was investigated by keeping the drain source voltage V DS constant at 2 V and by only varying the gate bias voltage V GS from 0 to 3 V. The strongest sensing response obtained from the device was around 0.547 mA ppb -1 at V GS  = 3 V, which is 63.7% higher in comparison to the response achieved at 0 V which shows a sensing response of around 0.334 mA ppb -1 . The current response depicts that the fabricated device is very sensitive and selective towards Hg 2+ ions. Moreover, the detection limit of our sensor at 3 V was calculated around 6.21 ppt, which attributes to the strong field created between the gate electrode and the HEMT channel due to the presence of 1T metallic phase in synthesized MoS 2 , indicating that the lower detection limits are achievable in adequate strong fields.