We report intrinsic photoconductivity studies on one of the least examined layered compounds,ZrS2.Few-atomic layer ZrS2 field-effect transistors were fabricated on the Si/SiO2 substrate and photoconductivity measureme...We report intrinsic photoconductivity studies on one of the least examined layered compounds,ZrS2.Few-atomic layer ZrS2 field-effect transistors were fabricated on the Si/SiO2 substrate and photoconductivity measurements were performed using both two-and four-terminal configurations under the illumination of 532 nm laser source.We measured photocurrent as a function of the incident optical power at several source-drain(bias)voltages.We observe a significantly large photoconductivity when measured in the multiterminal(four-terminal)configuration compared to that in the two-terminal configuration.For an incident optical power of 90 nW,the estimated photosensitivity and the external quantum efficiency(EQE)measured in two-terminal configuration are 0.5 A/W and 120%,respectively,under a bias voltage of 650 mV.Under the same conditions,the four-terminal measurements result in much higher values for both the photoresponsivity(R)and EQE to 6 A/W and 1400%,respectively.This significant improvement in photoresponsivity and EQE in the four-terminal configuration may have been influenced by the reduction of contact resistance at the metal-semiconductor interface,which greatly impacts the carrier mobility of low conducting materials.This suggests that photoconductivity measurements performed through the two-terminal configuration in previous studies on ZrS2 and other 2D materials have severely underestimated the true intrinsic properties of transition metal dichalcogenides and their remarkable potential for optoelectronic applications.展开更多
Conventional metasurfaces have demonstrated efficient wavefront manipulation by using thick and high-aspect-ratio nanostructures in order to eliminate interactions between adjacent phase-shifter elements.Thinner-than-...Conventional metasurfaces have demonstrated efficient wavefront manipulation by using thick and high-aspect-ratio nanostructures in order to eliminate interactions between adjacent phase-shifter elements.Thinner-than-wavelength dielectric metasurfaces are highly desirable because they can facilitate fabrication and integration with both electronics and mechanically tunable platforms.Unfortunately,because their constitutive phase-shifter elements exhibit strong electromagnetic coupling between neighbors,the design requires a global optimization methodology that considers the non-local interactions.Here,we propose a global evolutionary optimization approach to inverse design non-local metasurfaces.The optimal designs are experimentally validated,demonstrating the highest efficiencies for the thinnest transmissive metalenses reported to-date for visible light.In a departure from conventional design methods based on the search of a library of pre-determined and independent meta-atoms,we take full advantage of the strong interactions among nanoresonators to improve the focusing efficiency of metalenses and demonstrate that efficiency improvements can be obtained by lowering the metasurface filling factors.展开更多
基金N.R.P.acknowledged NSF-PREM through NSFDMR-1826886,HBCU-UP Excellence in research NSFDMR-1900692A portion of this work was performed at the National High Magnetic Field Laboratory,which is supported by the National Science Foundation Cooperative Agreement No.DMR-1644779+1 种基金the State of Florida.This work was performed,in part,at the Center for Nanoscale Materials,a U.S.Department of Energy Office of Science User Facilitysupported by the U.S.Department of Energy,Office of Science,under Contract No.DE-AC02-06CH11357.
文摘We report intrinsic photoconductivity studies on one of the least examined layered compounds,ZrS2.Few-atomic layer ZrS2 field-effect transistors were fabricated on the Si/SiO2 substrate and photoconductivity measurements were performed using both two-and four-terminal configurations under the illumination of 532 nm laser source.We measured photocurrent as a function of the incident optical power at several source-drain(bias)voltages.We observe a significantly large photoconductivity when measured in the multiterminal(four-terminal)configuration compared to that in the two-terminal configuration.For an incident optical power of 90 nW,the estimated photosensitivity and the external quantum efficiency(EQE)measured in two-terminal configuration are 0.5 A/W and 120%,respectively,under a bias voltage of 650 mV.Under the same conditions,the four-terminal measurements result in much higher values for both the photoresponsivity(R)and EQE to 6 A/W and 1400%,respectively.This significant improvement in photoresponsivity and EQE in the four-terminal configuration may have been influenced by the reduction of contact resistance at the metal-semiconductor interface,which greatly impacts the carrier mobility of low conducting materials.This suggests that photoconductivity measurements performed through the two-terminal configuration in previous studies on ZrS2 and other 2D materials have severely underestimated the true intrinsic properties of transition metal dichalcogenides and their remarkable potential for optoelectronic applications.
基金This work was performed at the Center for Nanoscale Materials,a U.S.Department of Energy Office of Science User Facility,and supported by the U.S.Department of Energy,Office of Science,under Contract No.DE-AC02-06CH11357This research used resources of the National Energy Research Scientific Computing Center,a U.S.Department of Energy Office of Science User Facility,supported by the U.S.Department of Energy,Office of Science,under Contract No.DE-AC02-05CH11231.
文摘Conventional metasurfaces have demonstrated efficient wavefront manipulation by using thick and high-aspect-ratio nanostructures in order to eliminate interactions between adjacent phase-shifter elements.Thinner-than-wavelength dielectric metasurfaces are highly desirable because they can facilitate fabrication and integration with both electronics and mechanically tunable platforms.Unfortunately,because their constitutive phase-shifter elements exhibit strong electromagnetic coupling between neighbors,the design requires a global optimization methodology that considers the non-local interactions.Here,we propose a global evolutionary optimization approach to inverse design non-local metasurfaces.The optimal designs are experimentally validated,demonstrating the highest efficiencies for the thinnest transmissive metalenses reported to-date for visible light.In a departure from conventional design methods based on the search of a library of pre-determined and independent meta-atoms,we take full advantage of the strong interactions among nanoresonators to improve the focusing efficiency of metalenses and demonstrate that efficiency improvements can be obtained by lowering the metasurface filling factors.
