Dielectric-Free Molybdenum Disulfide Transistors with In-Plane Gates.

In this work, we realize bilayer molybdenum disulfide (MoS) transistors with in-plane gates on sapphire substrates. Through sequential transferring of MoS, e-beam lithography, and metal lift-off, a device with channel width/length of 500:400 nm is fabricated. With a 250 nm separation between the in-plane gate and MoS channel, a drain current as high as 37 μA with a clear saturation region is observed. The device shows a high ON/OFF current ratio over 10, small gate bias required for current modulation, and high responsivity about 230 A/W when operated in the phototransistor mode. The gain of the phototransistor reaches 432. A quick calculation from the transfer curve using the formula of conventional transistors gives a field-effect mobility of 6365.9 cm·V·s, which, although overestimated, still suggests good performance of the device. With an additional MoS layer to isolate the MoS channel from the influence of the substrate, this dielectric-free in-plane gate transistor has exhibited potential in electronics. The high responsivity of the device under relatively low applied voltages is also promising for weak-light detection.