Browsing by Author "Pradhan, N.R."

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    Hall and field-effect mobilities in few layeredﾠp-WSe2ﾠfield-effect transistors
    (Macmillan Publishers Limited, 2015) Pradhan, N.R.; Rhodes, D.; Memaran, S.; Poumirol, J.M.; Smirnov, D.; Talapatra, S.; Feng, S.; Perea-Lopez, N.; Elias, A.L.; Terrones, M.; Ajayan, P.M.; Balicas, L.
    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 cm(2)/Vs at T = 300 K. The hole Hall mobility reaches a maximum value of 650 cm(2)/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.
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    Intrinsic carrier mobility of multi-layered MoS2 field-effect transistors on SiO2
    (American Institute of Physics, 2013) Pradhan, N.R.; Rhodes, D.; Zhang, Q.; Talapatra, S.; Terrones, M.; Ajayan, P.M.; Balicas, L.
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    Universal ac conduction in large area atomic layers of CVD-grown MoS2
    (American Physical Society, 2014) Ghosh, S.; Najmaei, S.; Kar, S.; Vajtai, R.; Lou, J.; Pradhan, N.R.; Balicas, L.; Ajayan, P.M.; Talapatra, S.
    Here, we report on the ac conductivity [σ’(ω); 10 mHz < ω < 0.1 MHz] measurements performed on atomically thin, two-dimensional layers of MoS2 grown by chemical vapor deposition (CVD). Σ’(ω) is observed to display a “universal” power law, i.e., σ’(ω) ∼ ωs measured within a broad range of temperatures, 10 K< T <340 K. The temperature dependence of ‘‘s” indicates that the dominant ac transport conduction mechanism in CVD-grown MoS2 is due to electron hopping through a quantum mechanical tunneling process. The ac conductivity also displays scaling behavior, which leads to the collapse of the ac conductivity curves obtained at various temperatures into a single master curve. These findings establish a basis for our understanding of the transport mechanism in atomically thin, CVD-grown MoS2 layers.