Du Xiang

Surface transfer doping induced effective modulation on ambipolar characteristics of few-layer black phosphorus

Black phosphorus, a fast emerging two-dimensional material, has been configured as field effect transistors, showing a hole-transport-dominated ambipolar characteristic. Here we report an effective modulation on ambipolar characteristics of few-layer black phosphorus transistors through in situ surface functionalization with caesium carbonate (Cs2CO3) and molybdenum trioxide (MoO3), respectively. Cs2CO3 is found to strongly electron dope black phosphorus. The electron mobility of black phosphorus is significantly enhanced to ~27 cm(2) V(-1) s(-1) after 10 nm Cs2CO3 modification, indicating a greatly improved electron-transport behaviour. In contrast, MoO3 decoration demonstrates a giant hole-doping effect. In situ photoelectron spectroscopy characterization reveals significant surface charge transfer occurring at the dopants/black phosphorus interfaces. Moreover, the surface-doped black phosphorus devices exhibit a largely enhanced photodetection behaviour. Our findings coupled with the tunable nature of the surface transfer doping scheme ensure black phosphorus as a promising candidate for further complementary logic electronics.

Electron-Doping-Enhanced Trion Formation in Monolayer Molybdenum Disulfide Functionalized with Cesium Carbonate

We report effective and stable electron doping of monolayer molybdenum disulfide (MoS2) by cesium carbonate (Cs2CO3) surface functionalization. The electron charge carrier concentration in exfoliated monolayer MoS2 can be increased by about 9 times after Cs2CO3 functionalization. The n-type doping effect was evaluated by in situ transport measurements of MoS2 field-effect transistors (FETs) and further corroborated by in situ ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering measurements. The electron doping enhances the formation of negative trions (i.e., a quasiparticle comprising two electrons and one hole) in monolayer MoS2 under light irradiation and significantly reduces the charge recombination of photoexcited electron-hole pairs. This results in large photoluminescence suppression and an obvious photocurrent enhancement in monolayer MoS2 FETs.

Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus

Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity ∼3 × 10(13) Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to ∼9 × 10(4) A W(-1) by applying a source-drain bias (VSD) of 3 V, which is the highest ever measured in any 2D material and 10(7) times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature.

Gap States Assisted MoO3 Nanobelt Photodetector with Wide Spectrum Response

Molybdenum oxides have been widely investigated for their broad applications ranging from electronics to energy storage. Photodetectors based on molybdenum trioxide (MoO3), however, were seldom reported owing to their low conductivity and weak photoresponse. Herein we report a photodetector based on single MoO3 nanobelt with wide visible spectrum response by introducing substantial gap states via H2 annealing. The pristine MoO3 nanobelt possessed low electrical conductance and no photoresponse for nearly all visible lights. The H2 annealing can significantly improve the conductance of MoO3 nanobelt, and result in a good photodetector with wide visible spectrum response. Under illumination of 680 nm light, the photodetector exhibited high responsivity of ~56 A/W and external quantum efficiency of ~10200%. As corroborated by in situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy investigations, such strong wide spectrum photoresponse arises from the largely enriched gap states in the MoO3 nanobelt after H2 annealing.

Surface Transfer Doping-Induced, High-Performance Graphene/Silicon Schottky Junction-Based, Self-Powered Photodetector

restricted due to the local perturbations within the device depletion regions. [ 8,9 ] Self-powered photodetectors based on photovoltaic effect are able to be operated without external bias. [ 3,10–12 ] Attributed to the large existing built-in electrical potential in self-powered photodetectors, the photogenerated electron–hole pairs can be separated at zero bias and thus contribute to the photoconduction. [ 3 ]

Water‐Catalyzed Oxidation of Few‐Layer Black Phosphorous in a Dark Environment

Black phosphorus (BP) shows great potential in electronic and optoelectronic devices owing to its semiconducting properties, such as thickness-dependent direct bandgap and ambipolar transport characteristics. However, the poor stability of BP in air seriously limits its practical applications. To develop effective schemes to protect BP, it is crucial to reveal the degradation mechanism under various environments. To date, it is generally accepted that BP degrades in air via light-induced oxidation. Herein, we report a new degradation channel via water-catalyzed oxidation of BP in the dark. When oxygen co-adsorbs with highly polarized water molecules on BP surface, the polarization effect of water can significantly lower the energy levels of oxygen (i.e. enhanced electron affinity), thereby facilitating the electron transfer from BP to oxygen to trigger the BP oxidation even in the dark environment. This new degradation mechanism lays important foundation for the development of proper protecting schemes in black phosphorus-based devices.

Improving chemical vapor deposition graphene conductivity using molybdenum trioxide: An in-situ field effect transistor study

By using in situ field effect transistor characterization integrated with molecular beam epitaxy technique, we demonstrate the strong surface transfer p-type doping effect of single layer chemical vapor deposition (CVD) graphene, through the surface functionalization of molybdenum trioxide (MoO3) layer. After doping, both the hole and electron mobility of CVD graphene are nearly retained, resulting in significant enhancement of graphene conductivity. With coating of 10 nm MoO3, the conductivity of CVD graphene can be increased by about 7 times, showing promising application for graphene based electronics and transparent, conducting, and flexible electrodes.

Surface Functionalization of Black Phosphorus via Potassium toward High-Performance Complementary Devices

Two-dimensional black phosphorus configured field-effect transistor devices generally show a hole-dominated ambipolar transport characteristic, thereby limiting its applications in complementary electronics. Herein, we demonstrate an effective surface functionalization scheme on few-layer black phosphorus, through in situ surface modification with potassium, with a view toward high performance complementary device applications. Potassium induces a giant electron doping effect on black phosphorus along with a clear bandgap reduction, which is further corroborated by in situ photoelectron spectroscopy characterizations. The electron mobility of black phosphorus is significantly enhanced to 262 (377) cm2 V-1 s-1 by over 1 order of magnitude after potassium modification for two-terminal (four-terminal) measurements. Using lithography technique, a spatially controlled potassium doping technique is developed to establish high-performance complementary devices on a single black phosphorus nanosheet, for example, the p-n homojunction-based diode achieves a near-unity ideality factor of 1.007 with an on/off ratio of ∼104. Our findings coupled with the tunable nature of in situ modification scheme enable black phosphorus as a promising candidate for further complementary electronics.

Electron transport and visible light absorption in a plasmonic photocatalyst based on strontium niobate

Semiconductor compounds are widely used for water splitting applications, where photo-generated electron-hole pairs are exploited to induce catalysis. Recently, powders of a metallic oxide (Sr

Tuning the electronic properties of ZnO nanowire field effect transistors via surface functionalization

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