Accurate change of carrier types within ultrathin MoTe2 field-effect transistors with the time exposed to ambient air

Doping of MoTe2 via Surface Charge Transfer in Air

“…Another aspect in which this work complements the literature is that we present a direct assessment of the charge transfer at the MoTe 2 surface, both experimentally (via work function measurements) and theoretically (via DFT calculations). Most literature reports use more “downstream” measurements such as transport measurements (or I / V characteristics) − or photoelectric characterizations. ,,, As such, our results provide an important piece of the puzzle in that it is a direct evidence of SCTD process and its tunability via oxygen concentration on the surface. Furthermore, we also illustrate local control of the surface charge doping by contact electrification using the probe of an electrostatic force microscope as a floating gate.…”

“…42 Due to air adsorption, a gradual change in conductivity (from ambipolar to p-type) was also observed over a period of 100 days on MoTe 2 field-effect transistors exposed to air. 43 Similarly, the ambient exposure for a prolonged period was found to be responsible for the surface charge accumulation in MoS 2 flakes due to a slow oxidation of the outer layers; 44,45 in this last case, the surface charge accumulation was in terms of electrons, making the MoS 2 surface highly n-doped and promoting a surface-dominant 2D current transport. In previous works, the effect of SCTD on TMDCs was inferred mostly from transport measurements [37][38][39]41 and photoelectric characterizations, e.g., Raman, photoluminescence, and XPS measurements, 35,36,43,44 which predominantly show the bulk response of materials.…”

“…SCTD is also relevant for tuning the electrical and optical properties from the perspective of fabricating complementary integrated circuits, sensors, optoelectronic, photovoltaic, and other devices. − In terms of materials, SCTD doping was reported for MoS 2 , , MoTe 2 , − and black phosphorus . Due to air adsorption, a gradual change in conductivity (from ambipolar to p -type) was also observed over a period of 100 days on MoTe 2 field-effect transistors exposed to air . Similarly, the ambient exposure for a prolonged period was found to be responsible for the surface charge accumulation in MoS 2 flakes due to a slow oxidation of the outer layers; , in this last case, the surface charge accumulation was in terms of electrons, making the MoS 2 surface highly n -doped and promoting a surface-dominant 2D current transport.…”

“…In previous works, the effect of SCTD on TMDCs was inferred mostly from transport measurements − , and photoelectric characterizations, e.g., Raman, photoluminescence, and XPS measurements, ,,, which predominantly show the bulk response of materials. As device miniaturization continues, the surface contribution to the electrical response of low-dimensional materials becomes comparable or even surpasses the bulk contribution.…”

Suspended MoTe2 field effect transistors with ionic liquid gate

“…This observation is consistent with previous studies on the oxygen interaction with MoTe2 FETs. 19,40 In Fig. 3(b), the transfer curves of a IL-gated device recorded over 27 days are shown.…”