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Register a new userPhotoconductivity of few-layered p-WSe2 phototransistors via multi-terminal measurements
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Recently, two-dimensional materials and in particular transition metal dichalcogenides (TMDs) were extensively studied because of their strong light-matter interaction and the remarkable optoelectronic response of their field-effect transistors (FETs). Here, we report a photoconductivity study from FETs built from few-layers of p-WSe2 measured in a multi-terminal configuration under illumination by a 532 nm laser source. The photogenerated current was measured as a function of the incident optical power, of the drain-to-source bias and of the gate voltage. We observe a considerably larger photoconductivity when the phototransistors were measured via a four-terminal configuration when compared to a two-terminal one. For an incident laser power of 248 nW, we extract 18 A/W and ~4000% for the two-terminal responsivity (R) and the concomitant external quantum efficiency (EQE) respectively, when a bias voltage Vds = 1 V and a gate voltage Vbg = 10 V are applied to the sample. R and EQE are observed to increase by 370% to ~85 A/W and ~20000% respectively, when using a four-terminal configuration. Thus, we conclude that previous reports have severely underestimated the optoelectronic response of transition metal dichalcogenides, which in fact reveals a remarkable potential for photosensing applications.
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We study electrical transport properties in exfoliated molybdenum disulfide (MoS2) back-gated field effect transistors at low drain bias and under different illumination intensities. It is found that photoconductive and photogating effect as well as space charge limited conduction can simultaneously occur. We point out that the photoconductivity increases logarithmically with the light intensity and can persist with a decay time longer than 10^4 s, due to photo-charge trapping at the MoS2/SiO2 interface and in MoS2 defects. The transfer characteristics present hysteresis that is enhanced by illumination. At low drain bias, the devices feature low contact resistance of 1.4 k{Omega}/{mu}m, ON current as high as 1.25 nA/{mu}m, 10^5 ON-OFF ratio, mobility of 1 cm^2/Vs and photoresponsivity R=1 A/W.
We report high performance p-type field-effect transistors based on single layered (thickness, ~0.7 nm) WSe2 as the active channel with chemically doped source/drain contacts and high-{kappa} gate dielectrics. The top-gated monolayer transistors exhibit a high effective hole mobility of ~250 cm2/Vs, perfect subthreshold swing of ~60 mV/dec, and ION/IOFF of >10^6 at room temperature. Special attention is given to lowering the contact resistance for hole injection by using high work function Pd contacts along with degenerate surface doping of the contacts by patterned NO2 chemisorption on WSe2. The results here present a promising material system and device architecture for p-type monolayer transistors with excellent characteristics.
Conducting nanowires possess remarkable physical properties unattainable in bulk materials. However our understanding of their transport properties is limited by the difficulty of connecting them electrically. In this Letter we investigate phototransport in both bulk silicon and silicon nanowires using a superconducting multimode resonator operating at frequencies between 0.3 and 3 GHz. We find that whereas the bulk Si response is mainly dissipative, the nanowires exhibit a large dielectric polarizability. This technique is contactless and can be applied to many other semiconducting nanowires and molecules. Our approach also allows to investigate the coupling of electron transport to surface acoustic waves in bulk Si and to electro-mechanical resonances in the nanowires.
We fabricate high-mobility p-type few-layer WSe2 field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level (LL) crossing effects at ultra-low coincident angles, revealing that the Zeeman energy is about three times as large as the cyclotron energy near the valence band top at {Gamma} valley. This result implies the significant roles played by the exchange interactions in p-type few-layer WSe2, in which itinerant or QH ferromagnetism likely occurs. Evidently, the {Gamma} valley of few-layer WSe2 offers a unique platform with unusually heavy hole-carriers and a substantially enhanced g-factor for exploring strongly correlated phenomena.
We present a theoretical study of the phase-coherent DC conductivity of few-layered antimonene in the presence of surface disorder. It is well known that while a single layer is a trivial semiconductor, multiple layers (typically a minimum of $approx$ 7) turn into a semi-metal with a nontrivial topological invariant featuring protected and decoupled surface states. We employ the finite-size Kubo formalism based on density functional theory calculations to show that the conductivity is amply dominated by the topological surface states even without bulk disorder. More importantly, the conductivity of the surface states does not show traces of a metal-insulator transition while the bulk ones can be driven towards an insulating phase in presence of only surface disorder. These results suggest that few-layered antimonene, despite not being insulating in the bulk, can present many of the advantages attributed to topological insulators under very general experimental conditions.
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