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Interplay of charge transfer and disorder in optoelectronic response in Graphene/hBN/MoS<sub>2</sub> van der Waals heterostructures
摘要： Strong optoelectronic response in the binary van der Waals heterostructures of graphene and transition metal dichalcogenides (TMDCs) is an emerging route towards high-sensitivity light sensing. While the high sensitivity is an effect of photogating of graphene due to inter-layer transfer of photo-excited carriers, the impact of intrinisic defects, such as traps and mid-gap states in the chalcogen layer remain largely unexplored. Here we employ graphene/hBN (hexagonal boron nitride)/MoS2 (molybdenum disulphide) trilayer heterostructures to explore the photogating mechanism, where the hBN layer acts as interfacial barrier to tune the charge transfer timescale. We find two new features in the photoresponse: First, an unexpected positive component in photoconductance upon illumination at short times that preceeds the conventional negative photoconductance due to charge transfer, and second, a strong negative photoresponse at infrared wavelengths (up to 1720 nm) well-below the band gap of single layer MoS2. Detailed time and gate voltage-dependence of the photoconductance indicates optically-driven charging of trap states as possible origin of these observations. The responsivity of the trilayer structure in the infrared regime was found to be extremely large (> 108 A/W at 1550 nm using 20 mV source drain bias at 180 K temperature and ≈ ?30 V back gate voltage). Our experiment demonstrates that interface engineering in the optically sensitive van der Waals heterostructures may cast crucial insight onto both inter- and intra-layer charge reorganization processes in graphene/TMDC heterostructures.
关键词： defects and disorders in TMDCs,monolayer MoS2,phototransistor,graphene,infrared photodetection,Van der Waals heterostructures
更新于2025-09-23 15:19:57
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Nanoscale Interfaces of Janus Monolayers of Transition Metal Dichalcogenides for 2D Photovoltaic and Piezoelectric Applications
摘要： Using first-principles calculations, we demonstrate a combination of two emergent fields, type-II van der Waal heterostructures and Janus structures, for the purpose of optimizing the harvesting of solar and nanoelectromechanical energy. The most stable stacking order in these nanoscale heterobilayers comprising of Janus monolayers of transition metal dichalcogenides has been ascertained based on the interlayer binding energies. The binding energies in WSeTe/WSTe and MoSeTe/WSTe heterobilayers are found to be -27.93 and -25.67 meV/?2 at an equilibrium interlayer layer distance of 3.25 ? and 3.32 ? respectively, indicating the exothermicity in the process of heterobilayer formation and hence, its experimental feasibility. The mechanical and dynamical stabilities have also been confirmed for these heterobilayers using the Born Huang stability criteria and phonon dispersion calculations. Our results unveil the mechanism underlying the electronic, piezoelectric, photocatalytic properties and carrier mobility in these Janus heterobilayers. Power conversion efficiency in the 2D ultrathin excitonic solar cells constituted by some of the heterobilayers studied in this work, has been found to lie in the range of 15-20%. Moreover, a very high carrier mobility (>200 cm2/V.s) together with a large visible light absorption coefficient (α ~ 105 cm-1) has been observed in these hetero-bilayers. The piezoelectric coefficients in these ultrathin heterobilayers (d33 = 13.91 pm/V) is found to reach close to the values obtained in multilayer/bulk structures built from Janus monolayers of Mo-based dichalcogenides. Our findings highlight the promising applications of these heterobilayers in ultrathin excitonic solar cells, nanoelectronics and nanopiezotronics.
关键词： van der Waals heterostructures,transition metal dichalcogenides,photovoltaic applications,Janus monolayers,piezoelectricity,carrier mobility
更新于2025-09-23 15:19:57
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Monolithic Contact Engineering to Boost Optoelectronic Performances of 2D Semiconductor Photovoltaic Heterojunctions
摘要： In optoelectronic devices based on two-dimensional (2D) semiconductor heterojunctions, the efficient charge transport of photogenerated carriers across the interface is a critical factor to determine the device performances. Here, we report an unexplored approach to boost the optoelectronic device performances of the WSe2-MoS2 p-n heterojunctions via the monolithic-oxidation-induced doping and resultant modulation of the interface band alignment. In the proposed device, the atomically thin WOx layer, which is directly formed by layer-by-layer oxidation of WSe2, is used as a charge transport layer for promoting hole extraction. The use of the ultrathin oxide layer significantly enhanced the photoresponsivity of the WSe2-MoS2 p-n junction devices, and the power conversion efficiency increased from 0.7 to 5.0%, maintaining the response time. The enhanced characteristics can be understood by the formation of the low Schottky barrier and favorable interface band alignment, as confirmed by band alignment analyses and first-principle calculations. Our work suggests a new route to achieve interface contact engineering in the heterostructures toward realizing high-performance 2D optoelectronics.
关键词： Contact engineering,Transition metal dichalcogenides,Heterostructures,Photovoltaics,2D semiconductors,Optoelectronics
更新于2025-09-23 15:19:57
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Gatea??Couplinga??Enabled Robust Hysteresis for Nonvolatile Memory and Programmable Rectifier in Van der Waals Ferroelectric Heterojunctions
摘要： Ferroelectric field-effect transistors (FeFETs) are one of the most interesting ferroelectric devices; however, they, usually suffer from low interface quality. The recently discovered 2D layered ferroelectric materials, combining with the advantages of van der Waals heterostructures (vdWHs), may be promising to fabricate high-quality FeFETs with atomically thin thickness. Here, dual-gated 2D ferroelectric vdWHs are constructed using MoS2, hexagonal boron nitride (h-BN), and CuInP2S6 (CIPS), which act as a high-performance nonvolatile memory and programmable rectifier. It is first noted that the insertion of h-BN and dual-gated coupling device configuration can significantly stabilize and effectively polarize ferroelectric CIPS. Through this design, the device shows a record-high performance with a large memory window, large on/off ratio (107), ultralow programming state current (10?13 A), and long-time endurance (104 s) as nonvolatile memory. As for programmable rectifier, a wide range of gate-tunable rectification behavior is observed. Moreover, the device exhibits a large rectification ratio (3 × 105) with stable retention under the programming state. This demonstrates the promising potential of ferroelectric vdWHs for new multifunctional ferroelectric devices.
关键词： nonvolatile memory,programmable rectifiers,ferroelectrics,dual-gated coupling,van der Waals heterostructures,2D
更新于2025-09-23 15:19:57
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Facet-energy inspired metal oxide extended hexapod decorated with graphene quantum dots: Sensitive detection of bisphenol A in live cells
摘要： The development of crystal-facet metal oxide heterostructures has been of great interest owing to their rational design and multi-functioning properties at the nanoscale level. Herein, we report a facile solution-based method for the synthesis of single-crystal Cu2O nanostructures (i.e. Cu2O-CuO) as a core. The graphene quantum dots (GQDs) with varying concentrations are harvested on the surface of Cu2O extended hexapods (EHPs) in ethanol solution at room temperature via self-assembly, where copper acts as a sacrificial model and stabilizer as well. The Cu2O crystals displayed a good sensing activity toward BPA oxidation owing to high energy facets, dangling bonds and great proportion of surface copper atoms. The structural, morphological, chemical and vibrational investigations were attained in detail, presenting high crystallinity of the hybrid nanocomposite and Cu2O-CuO heterojunction positions along with the growth of GQDs on the core of Cu2O-CuO crystal. The electrochemical sensing performance of as-fabricated Cu2O-CuO@GQDs EHPs has been monitored for the determination of bisphenol A (BPA) as an early diagnostic marker and environmental contaminant. The synergy effect of boosted surface area, exposed Cu {111} crystallographic planes and mixed copper valences enhance redox reaction kinetics by increasing the electron shuttling rate at the electrode-analyte junction. Benefitted from the improved electrocatalytic activity for BPA oxidation, the electrochemical sensor displayed the lowest limit of detection (≤1 nM), good chemical stability and broad linear range (2 nM - 11 mM), and high sensitivity (636 μA mM-1 cm-2). The Cu2O-CuO@GQDs EHPs based sensing platform has been applied for BPA detection in water and human serum samples. We have also constructed up a pioneering electrochemical sensing podium for BPA detection in live cells which might be used as a marker in early disease diagnosis.
关键词： electrochemical sensor,bisphenol A,live cells,graphene quantum dots,crystal-facet metal oxide heterostructures
更新于2025-09-23 15:19:57
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Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells
摘要： n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device.
关键词： quantum wells,THz spectroscopy,group IV epitaxy,intersubband transitions,silicon–germanium heterostructures
更新于2025-09-23 15:19:57
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Direct conjugation with a zero length linker of fullerene C <sub/>70</sub> to ZnO quantum dots for multicolor light-emitting diodes
摘要： Environmentally friendly metal oxide quantum dots (QDs) nanostructures has become attractive alternative materials for replacing QDs containing toxic elements of Cd and Pb. Although many attempts have been proposed for optoelectronic applications of hybrid metal oxide QDs with tailored opto-electronic properties, the fabrication of heterogeneous QD-fullerene hybrids as an emissive material has been little studied for optoelectronic devices. Herein, we report the preparation of ZnO-fullerene C70 (ZnO-C70) QDs by facile chemical reaction with zero length linker and demonstrate whitish light-emitting diodes by fullerene induced multicolor emission from ZnO-C70 QDs heterostructure. The electroluminescence (EL) is attributed to three new emission features in the visible region that originates from the electron transitions from three split lowest unoccupied molecular orbital levels of C70 molecules to the valence band of ZnO QDs. Compared with photoluminescence, the EL emissions were red-shifted by 50 - 130 meV due to the interaction between ZnO-C70 QDs in solid state. Energy levels of C70 were also suitably aligned to those of ZnO QDs with lower electron transfer barrier of 0.22 eV, which offers an advantageous route for electron transport. Consequently, the environmentally friendly ZnO-C70 QDs with extraordinary properties promise great potential for use as novel encapsulating materials in the field of opto-electronic applications adopting QDs.
关键词： Fullerene C70,Light emitting diodes,ZnO-fullerene C70 heterostructure,C60,Quantum dots,0D-0D heterostructures
更新于2025-09-23 15:19:57
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Organic-inorganic hybrid heterostructures towards long-wavelength photodetectors based on InGaZnO-Polymer
摘要： Organic-inorganic hybrid heterostructures have attracted considerable attentions due to their wide application in electronics and optoelectronics. In this study, a high-performance red light photodetector based on organic-inorganic heterostructure was successfully fabricated after a systematical optimization in material and device constitution. The conjugated polymer (P(PDI-BDT-O)) with narrow band gap used as light absorber was combined with a layer of indium gallium zinc oxide (IGZO) to construct a bi-layered phototransistor achieving a high mobility as well as high photoresponsivity. Benefiting from both the high absorption coefficient of the polymer over a wide range of wavelength and the perfect matching of band level between polymer and IGZO, the device exhibits an ultrahigh photoresponsivity (212 A/W) and specfic detectivity (2 ? 1012 Jones) for red light at the wavelength of 633 nm. These results demonstrate the great potential of organic-inorganic heterostructures in the application of long-wavelength photodetectors.
关键词： Conjugated polymer,Oxide semiconductor,Organic-inorganic heterostructures,Red light photodetector
更新于2025-09-23 15:19:57
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Modifying the Electronic Properties of Se/n‐Si Heterostructure Using Electrolysis
摘要： Heterostructures of dissimilar crystalline materials are key in the development of photoelectronic devices. Such structures rely on matching lattice constants for efficient transport. Nevertheless, an amorphous material, amorphous Se is becoming important in high-energy photoelectronics. Thus there is a need to understand the heterostructures it forms with conventional crystalline materials. Since the transport properties of such heterostructures will be limited by lattice mismatches, methods to improve transport are necessary. We investigated the effect of electrolysis on the electronic properties of Se based multilayer films deposited on n-type silicon (Se/n-Si) and showed that conduction and photoresponse can be changed by electrolysis processing. The Se surface of the Se/n-Si samples was used as an anode in the electrolysis of NaCl solution. Afterwards, the samples were measured using current–voltage and capacitance–voltage variations in dark conditions and under illumination. Electrolysis processed samples showed higher conduction current and photocurrent, compared to samples not used in electrolysis. This is due to the introduction of Cl into the Se, which affects carrier lifetimes: increasing hole lifetime and reducing electron lifetime. We therefore suggest that electrolysis can be applied to modify the electronic properties of Se/n-Si heterostructures.
关键词： chalcogenide semiconductor,amorphous selenium,heterostructures,electrochemical
更新于2025-09-23 15:19:57
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High‐Performance Photoinduced Memory with Ultrafast Charge Transfer Based on MoS <sub/>2</sub> /SWCNTs Network Van Der Waals Heterostructure
摘要： Photoinduced memory devices with fast program/erase operations are crucial for modern communication technology, especially for high-throughput data storage and transfer. Although some photoinduced memories based on 2D materials have already demonstrated desirable performance, the program/erase speed is still limited to hundreds of micro-seconds. A high-speed photoinduced memory based on MoS2/single-walled carbon nanotubes (SWCNTs) network mixed-dimensional van der Waals heterostructure is demonstrated here. An intrinsic ultrafast charge transfer occurs at the heterostructure interface between MoS2 and SWCNTs (below 50 fs), therefore enabling a record program/erase speed of ≈32/0.4 ms, which is faster than that of the previous reports. Furthermore, benefiting from the unique device structure and material properties, while achieving high-speed program/erase operation, the device can simultaneously obtain high program/erase ratio (≈106), appropriate storage time (≈103 s), record-breaking detectivity (≈1016 Jones) and multibit storage capacity with a simple program/erase operation. It even has a potential application as a flexible optoelectronic device. Therefore, the designed concept here opens an avenue for high-throughput fast data communications.
关键词： van der Waals heterostructures,program/erase performance,photoinduced memory,ultrafast charge transfer
更新于2025-09-23 15:19:57