Abstract
Here, we present a temperature (T) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe2 exfoliated onto SiO2. Without dielectric engineering and beyond a T-dependent threshold gate-voltage, we observe maximum hole mobilities approaching 350 cm2/Vs at T = 300 K. The hole Hall mobility reaches a maximum value of 650 cm2/Vs as T is lowered below ~150 K, indicating that insofar WSe2-based field-effect transistors (FETs) display the largest Hall mobilities among the transition metal dichalcogenides. The gate capacitance, as extracted from the Hall-effect, reveals the presence of spurious charges in the channel, while the two-terminal sheet resistivity displays two-dimensional variable-range hopping behavior, indicating carrier localization induced by disorder at the interface between WSe2 and SiO2. We argue that improvements in the fabrication protocols as, for example, the use of a substrate free of dangling bonds are likely to produce WSe2-based FETs displaying higher room temperature mobilities, i.e. approaching those of p-doped Si, which would make it a suitable candidate for high performance opto-electronics.
Highlights
We present a temperature (T) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe2 exfoliated onto SiO2
Inset: atomic force microscopy image collected from a lateral edge of the WSe2 crystal in (a). (c) Side view sketch of our field-effect transistor(s), indicating that the Ti/Au pads contact all atomic layers, and of the experimental configuration of measurements. (d) Room temperature field-effect mobility mFE as a function of crystal thickness extracted from several field-effect transistors (FETs) based on WSe2 exfoliated onto SiO2
In summary field-effect transistors based on multi-layered p-doped WSe2 can display peak hole Hall-mobilities in excess of 200 cm2/Vs at room temperature
Summary
We present a temperature (T) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe2 exfoliated onto SiO2. The hole Hall mobility reaches a maximum value of 650 cm2/Vs as T is lowered below ,150 K, indicating that insofar WSe2-based field-effect transistors (FETs) display the largest Hall mobilities among the transition metal dichalcogenides. Studies[7] on field-effect transistors (FETs) based on bulk WSe2 single-crystals using parylene as the gate dielectric, revealed room temperature field-effect mobilities approaching those of p-Si8 but with a small current ON/OFF ratio. It was recently argued that remote phonons from dielectric layers such as HfO2, can limit carrier mobility and would require the use of an interfacial layer to absorb most of the vibrational energy[14] These observations already led to the development of integrated circuits based on single15- and on bi-layered[16] MoS2. Marked discrepancies were reported between the measured field-effect and the Hall mobilities[17], which at the light of Refs. 11–13 could be attributed to underestimated values for the gate capacitances
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