Synthesis and field emission properties of topological insulator Bi₂Se₃ nanoflake arrays

High-Performance InSe Transistors with Ohmic Contact Enabled by Nonrectifying Barrier-Type Indium Electrodes

The electrical contact to two-dimensional (2D) semiconductor materials is decisive to the electronic performance of 2D semiconductor field-effect devices (FEDs). The presence of a Schottky barrier often leads to a large contact resistance, which seriously limits the channel conductance and carrier mobility measured in a two-terminal geometry. In contrast, Ohmic contact is desirable and can be achieved by the presence of a nonrectifying or tunneling barrier. Here, we demonstrate that a nonrectifying barrier can be realized by contacting indium (In), a low work function metal, with layered InSe because of a favorable band alignment at the In-InSe interface. The nonrectifying barrier is manifested by Ohmic contact behavior at T = 2 K and a low barrier height, Φ_B = 50 meV. This Ohmic contact enables demonstration of an on-current as large as 410 μA/μm, which is among the highest values achieved in FEDs based on layered semiconductors. A high electron mobility of 3700 and 1000 cm²/V·s is achieved with the two-terminal In-InSe FEDs at T = 2 K and room temperature, respectively, which can be attributed to enhanced quality of both conduction channel and the contacts. The improvement in the contact quality is further proven by an X-ray photoelectron spectroscopy study, which suggests that a reduction effect occurs at the In-InSe interface. The demonstration of high-performance In-InSe FEDs indicates a viable interface engineering method for next-generation, 2D semiconductor-based electronics.

Enhancement of field electron emission in topological insulator Bi2Se3 by Ni doping

Nanostructures of bismuth selenide (Bi₂Se₃), a 3D topological insulator material, and nickel (Ni) doped Bi₂Se₃ samples were prepared by a hydrothermal method to explore the field emission properties.

Enhancement of carrier transport characteristic in the Sb2Se2Te topological insulators by N2 adsorption

The carrier transport characteristics of Sb₂Se₂Te topological insulators were investigated, after exposure to different levels of nitrogen gas. The magnetoresistance (MR) slope for the Sb₂Se₂Te crystal increased by approximately 100% at 10 K after 2-days of exposure. The Shubnikov-de Haas (SdH) oscillation amplitude increased by 30% while oscillation frequencies remained the same. MR slopes and the mobilities had the same dependency on temperature over a wide temperature range. All measured data conformed to a linear correlation between MR slope and mobility, supporting our hypothesis that the MR increase and the SdH oscillation enhancement might be caused by mobility enhancement induced by adsorbed N₂ molecular.

rGO-Wrapped flowerlike Bi2Se3 nanocomposite: synthesis, experimental and simulation-based investigation on cold cathode applications

Bi₂Se₃ nanoflowers (NFs) – reduced graphene oxide (rGO) nanocomposite (BG) synthesized via cost-effective, ecofriendly and easy hydrothermal route: smart cold cathode for future display device.

High mobility, large linear magnetoresistance, and quantum transport phenomena in Bi2Te3 films grown by metallo-organic chemical vapor deposition (MOCVD)

We investigated the magnetotransport properties of Bi2Te3 films grown on GaAs (001) substrate by a cost-effective metallo-organic chemical vapor deposition (MOCVD). We observed the remarkably high carrier mobility and the giant linear magnetoresistance (carrier mobility ∼ 22 000 cm(2) V(-1) s(-1), magnetoresistance ∼ 750% at 1.8 K and 9 T for a 100 nm thick film) that depends on the film thickness. In addition, the Shubnikov-de Haas oscillation was observed, from which the effective mass was calculated to be consistent with the known value. From the thickness dependence of the Shubnikov-de Haas oscillation, it was found that a two dimensional electron gas with the conventional electron nature coexists with the topological Dirac fermion states and dominates the carrier transport in the Bi2Te3 film with thickness higher than 300 nm. These results are attributed to the intrinsic nature of Bi2Te3 in the high-mobility transport regime obtained by a deliberate choice of the substrate and the growth conditions.

Field electron emission of layered Bi₂Se₃ nanosheets with atom-thick sharp edges

Field electron emission properties of solution processed few-layer Bi₂Se₃ nanosheets are studied for the first time, which exhibit a low turn-on field of 2.3 V μm(-1), a high field enhancement factor of up to 6860 and good field emission stability. This performance is better than that of the as reported layered MoS₂f sheets and is comparable to that of single layer graphene films. The efficient field emission behaviours are found to be not only attributed to their lower work function but also related to their numerous sharp edges or protrusion decorated structure based on our simulation results. Besides, the contribution of possible two-dimensional electron gas surface states of atom-thick layered Bi₂Se₃ nanosheets is discussed in this paper. We anticipate that these solution processed layered Bi₂Se₃ nanosheets have great potential as robust high-performance vertical structure electron emitters for future light weight and highly flexible vacuum micro/nano-electronic device applications.

Identification of helicity-dependent photocurrents from topological surface states in Bi2Se3 gated by ionic liquid

Dirac-like surface states on surfaces of topological insulators have a chiral spin structure with spin locked to momentum, which is interesting in physics and may also have important applications in spintronics. In this work, by measuring the tunable helicity-dependent photocurrent (HDP), we present an identification of the HDP from the Dirac-like surface states at room temperature. It turns out that the total HDP has two components, one from the Dirac-like surface states, and the other from the surface accumulation layer. These two components have opposite directions. The clear gate tuning of the electron density as well as the HDP signal indicates that the surface band bending and resulted surface accumulation are successfully modulated by the applied ionic liquid gate, which provides a promising way to the study of the Dirac-like surface states and also potential applications in spintronic devices.

Facile fabrication of graphene-topological insulator Bi2Se3 hybrid Dirac materials via chemical vapor deposition in Se-rich conditions

Direct deposition of a uniform and high-quality Bi₂Se₃ thin film on a graphene film (layer controlled) is performed using a catalyst-free vapor deposition system in a Se-rich environment.