Wafer-scale synthesis of monolayer WS2 for high-performance flexible photodetectors by enhanced chemical vapor deposition

Two-dimensional （2D） nanomaterials have recently attracted considerable attention due to their promising applications in next-generation electronics and optoelectronics. In particular, the large-scale synthesis of high-quality 2D materials is an essential requirement for their practical applications. Herein, we demonstrate the wafer-scale synthesis of highly crystalline and homogeneous monolayer WS2 by an enhanced chemical vapor deposition （CVD） approach, in which precise control of the precursor vapor pressure can be effectively achieved in a multi-temperature zone horizontal furnace. In contrast to conventional synthesis methods, the obtained monolayer WS2 has excellent uniformity both in terms of crystallinity and morphology across the entire substrate wafer grown （e.g., 2 inches in diameter）, as corroborated by the detailed characterization. When incorporated in typical rigid photodetectors, the monolayer WS2 leads to a respectable photodetection performance, with a responsivity of 0.52 mA/W, a detectivity of 4.9 × 10^9 Jones, and a fast response speed （〈 560μs）. Moreover, once fabricated as flexible photodetectors on polyimide, the monolayer WS2 leads to a responsivity of up to 5 mA/W. Importantly, the photocurrent maintains 89% of its initial value even after 3,000 bending cycles. These results highlight the versatility of the present technique, which allows its applications in larger substrates, as well as the excellent mechanical flexibility and robustness of the CVD-grown, homogenous WS2 monolayers, which can promote the development of advanced flexible optoelectronic devices.

Crystalline InGaZnO quaternary nanowires with superlattice structure for high-performance thin-film transistors

Amorphous indium-gallium-zinc oxide (a-IGZO) materials have been widely explored for various thin-film transistor (TFT) applications;however, their device performance is still restricted by the intrinsic material issues especially due to their non-crystalline nature. In this study, highly crystalline superlattice-structured IGZO nanowires (NWs) with different Ga concentration are successfully fabricated by enhanced ambient-pressure chemical vapor deposition (CVD). The unique superlattice structure together with the optimal Ga concentration (i.e., 31 at.%) are found to effectively modulate the carrier concentration as well as efficiently suppress the oxygen vacancy formation for the superior NW device performance. In specific, the In1.8Ga1.8Zn2.4O7 NW field-effect transistor exhibit impressive device characteristics with the average electron mobility of ~ 110 cm^2-V^-1·s^-1 and on/off current ratio of ~ 10^6. Importantly, these NWs can also be integrated into NW parallel arrays for the construction of high-performance TFT devices, in which their performance is comparable to many state-of-the-art IGZO TFTs. All these results can evidently indicate the promising potential of these crystalline superlattice-structured IGZO NWs for the practical utilization in next-generation metal-oxide TFT device technologies.

High-performance enhancement-mode thin-film transistors based on Mg-doped In2O3 nanofiber networks

Although In2O3 nanofibers （NFs） are well-known candidates as active materials for next-generation, low-cost electronics, these NF based devices still suffer from high leakage current, insufficient on-off current ratios （Ion/Ioff）, and large, negative threshold voltages （VTH）, leading to poor device performance, parasitic energy consumption, and rather complicated circuit design. Here, instead of the conventional surface modification of In2O3 NFs, we present a one-step electrospinning process （i.e., without hot-press） to obtain controllable Mg-doped In2O3 NF networks to achieve high-performance enhancement-mode thin-film transistors （TFTs）. By simply adjusting the Mg doping concentration, the device performance can be manipulated precisely. For the optimal doping concentration of 2 mol%, the devices exhibit a small VTH （3.2 V）, high saturation current （1.1 × 10^-4 A）, large on/off current ratio （〉 10^8）, and respectable peak carrier mobility （2.04 cm2/（V.s））, corresponding to one of the best device performances among all 1D metal-oxide NFs based devices reported so far. When high-K HfOx thin films are employed as the gate dielectric, their electron mobility and VTH can be further improved to 5.30 cm^2/（V.s） and 0.9 V, respectivel）, which demonstrates the promising prospect of these Mg-doped In2O3 NF networks for high- performance, large-scale, and low-power electronics.