Abstract
An emerging electronic material as one of transition metal dichalcogenides (TMDCs), tungsten disulfide (WS2) can be exfoliated as an atomically thin layer and can compensate for the drawback of graphene originating from a gapless band structure. A direct bandgap, which is obtainable in single-layer WS2, is an attractive characteristic for developing optoelectronic devices, as well as field-effect transistors. However, its relatively low mobility and electrical characteristics susceptible to environments remain obstacles for the use of device materials. Here, we demonstrate remarkable improvement in the electrical characteristics of single-layer WS2 field-effect transistor (SL-WS2 FET) using chemical vapor deposition (CVD)-grown hexagonal BN (h-BN). SL-WS2 FET sandwiched between CVD-grown h-BN films shows unprecedented high mobility of 214 cm2/Vs at room temperature. The mobility of a SL-WS2 FET has been found to be 486 cm2/Vs at 5 K. The ON/OFF ratio of output current is ~107 at room temperature. Apart from an ideal substrate for WS2 FET, CVD-grown h-BN film also provides a protection layer against unwanted influence by gas environments. The h-BN/SL-WS2/h-BN sandwich structure offers a way to develop high-quality durable single-layer TMDCs electronic devices.
Highlights
We found that another SL-WS2 field-effect transistors (FETs) sandwiched between chemical vapor deposition (CVD)-grown hexagonal BN (h-BN) films showed the mobility of 214 cm2/Vs at room temperature
The CVD-grown h-BN film was transferred on Si substrate with 300 nm thick SiO2 top layer, and a SL-WS2 film was placed on top of the h-BN film by micromechanical cleavage method
To verify the role of our CVD-grown h-BN films, we investigated the existence of hysteresis in the transfer characteristics of SL-WS2 FETs by sweeping Vbg[18]
Summary
Characterization of single-layer WS2 by optical and atomic force microscopy. Figure 1a shows the schematic of a WS2 FET device sandwiched between CVD-grown h-BN films. Temperature-dependent electrical transport properties of SL-WS2 FETs. We have investigated the temperature-dependent electronic transport properties of SL-WS2 FETs. Figure 4d shows the transfer characteristics (Ids–Vbg) of the SL-WS2 FET sandwiched between CVD-grown h-BN films at Vds = 0.5 V at different temperatures. (d) Transfer characteristics (Ids–Vbg) of the mechanically exfoliated SL-WS2 FET enclosed by h-BN films at different temperatures. Larger standard deviation of intensity ratio of I2LA(M)/IA1g was found for SL-WS2 on the SiO2 substrate, whereas smaller standard deviation was found for h-BN/SL-WS2/h-BN This finding indicates that a higher uniformity of SL-WS2 quality can be achieved by enclosing the SL-WS2 with h-BN films
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