Xingqiang Liu

High‐Responsivity Graphene/InAs Nanowire Heterojunction Near‐Infrared Photodetectors with Distinct Photocurrent On/Off Ratios

Graphene is a promising candidate material for high-speed and ultra-broadband photodetectors. However, graphene-based photodetectors suffer from low photoreponsivity and I(light)/I(dark) ratios due to their negligible-gap nature and small optical absorption. Here, a new type of graphene/InAs nanowire (NW) vertically stacked heterojunction infrared photodetector is reported, with a large photoresponsivity of 0.5 AW(-1) and I(light)/I(dark) ratio of 5 × 10(2), while the photoresponsivity and I(light)/I(dark) ratio of graphene infrared photodetectors are 0.1 mAW(-1) and 1, respectively. The Fermi level (E(F)) of graphene can be widely tuned by the gate voltage owing to its 2D nature. As a result, the back-gated bias can modulate the Schottky barrier (SB) height at the interface between graphene and InAs NWs. Simulations further demonstrate the rectification behavior of graphene/InAs NW heterojunctions and the tunable SB controls charge transport across the vertically stacked heterostructure. The results address key challenges for graphene-based infrared detectors, and are promising for the development of graphene electronic and optoelectronic applications.

Rational design of amorphous indium zinc oxide/carbon nanotube hybrid film for unique performance transistors.

Here we report unique performance transistors based on sol-gel processed indium zinc oxide/single-walled carbon nanotube (SWNT) composite thin films. In the composite, SWNTs provide fast tracks for carrier transport to significantly improve the apparent field effect mobility. Specifically, the composite thin film transistors with SWNT weight concentrations in the range of 0-2 wt % have been investigated with the field effect mobility reaching as high as 140 cm(2)/V·s at 1 wt % SWNTs while maintaining a high on/off ratio ∼10(7). Furthermore, the introduction SWNTs into the composite thin film render excellent mechanical flexibility for flexible electronics. The dynamic loading test presents evidently superior mechanical stability with only 17% variation at a bending radius as small as 700 μm, and the repeated bending test shows only 8% normalized resistance variation after 300 cycles of folding and unfolding, demonstrating enormous improvement over the basic amorphous indium zinc oxide thin film. The results provide an important advance toward high-performance flexible electronics applications.

Transparent, High‐Performance Thin‐Film Transistors with an InGaZnO/Aligned‐SnO2‐Nanowire Composite and their Application in Photodetectors

A high mobility of 109.0 cm(2) V(-1) s(-1) is obtained by thin-film transistors (TFTs) comprising a composite made by aligning SnO2 nanowires (NWs) in amorphous InGaZnO (a-IGZO) thin films. This composite TFT reaches an on-current density of 61.4 μA μm(-1) with a 10 μm channel length. Its performance surpasses that of single-crystalline InGaZnO and is comparable with that of polycrystalline silicon.

Controllable Electrical Properties of Metal-Doped In2O3 Nanowires for High-Performance Enhancement-Mode Transistors

In recent years, In(2)O(3) nanowires (NWs) have been widely explored in many technological areas due to their excellent electrical and optical properties; however, most of these devices are based on In(2)O(3) NW field-effect transistors (FETs) operating in the depletion mode, which induces relatively higher power consumption and fancier circuit integration design. Here, n-type enhancement-mode In(2)O(3) NW FETs are successfully fabricated by doping different metal elements (Mg, Al, and Ga) in the NW channels. Importantly, the resulting threshold voltage can be effectively modulated through varying the metal (Mg, Ga, and Al) content in the NWs. A series of scaling effects in the mobility, transconductance, threshold voltage, and source-drain current with respect to the device channel length are also observed. Specifically, a small gate delay time (0.01 ns) and high on-current density (0.9 mA/μm) are obtained at 300 nm channel length. Furthermore, Mg-doped In(2)O(3) NWs are then employed to fabricate NW parallel array FETs with a high saturation current (0.5 mA), on/off ratio (>10(9)), and field-effect mobility (110 cm(2)/V·s), while the subthreshold slope and threshold voltage do not show any significant changes. All of these results indicate the great potency for metal-doped In(2)O(3) NWs used in the low-power, high-performance thin-film transistors.

Scalable Integration of Indium Zinc Oxide/Photosensitive‐Nanowire Composite Thin‐Film Transistors for Transparent Multicolor Photodetectors Array

By incorporating crystalline photosensitive nanowires (NWs), an amorphous InZnO (a-IZO) thin film is designed to be sensitive to the primary colors of light via a facile sol-gel approach. The mobility is also improved. The composite devices leverage the advantages of the transparency of a-IZO with the photosensitivity of CdS NWs.

Enhancing Photoresponsivity of Self-Aligned MoS2 Field-Effect Transistors by Piezo-Phototronic Effect from GaN Nanowires

We report high-performance self-aligned MoS2 field-effect transistors (FETs) with enhanced photoresponsivity by the piezo-phototronic effect. The FETs are fabricated based on monolayer MoS2 with a piezoelectric GaN nanowire (NW) as the local gate, and a self-aligned process is employed to define the source/drain electrodes. The fabrication method allows the preservation of the intrinsic property of MoS2 and suppresses the scattering center density in the MoS2/GaN interface, which results in high electrical and photoelectric performances. MoS2 FETs with channel lengths of ∼200 nm have been fabricated with a small subthreshold slope of 64 mV/dec. The photoresponsivity is 443.3 A·W(-1), with a fast response and recovery time of ∼5 ms under 550 nm light illumination. When strain is introduced into the GaN NW, the photoresponsivity is further enhanced to 734.5 A·W(-1) and maintains consistent response and recovery time, which is comparable with that of the mechanical exfoliation of MoS2 transistors. The approach presented here opens an avenue to high-performance top-gated piezo-enhanced MoS2 photodetectors.

Ferroelectric memory based on nanostructures

In the past decades, ferroelectric materials have attracted wide attention due to their applications in nonvolatile memory devices (NVMDs) rendered by the electrically switchable spontaneous polarizations. Furthermore, the combination of ferroelectric and nanomaterials opens a new route to fabricating a nanoscale memory device with ultrahigh memory integration, which greatly eases the ever increasing scaling and economic challenges encountered in the traditional semiconductor industry. In this review, we summarize the recent development of the nonvolatile ferroelectric field effect transistor (FeFET) memory devices based on nanostructures. The operating principles of FeFET are introduced first, followed by the discussion of the real FeFET memory nanodevices based on oxide nanowires, nanoparticles, semiconductor nanotetrapods, carbon nanotubes, and graphene. Finally, we present the opportunities and challenges in nanomemory devices and our views on the future prospects of NVMDs.

High-Mobility Solution-Processed Amorphous Indium Zinc

High-performance thin-film transistors with amorphous indium zinc oxide (IZO) films was deposited by embedding indium oxide nanocrystals (In₂O₃ NCs) into IZO films based on a sol-gel process. Excellent electrical properties have been demonstrated, including a field-effect mobility value of 32.6 cm²·V^-1·s^-1 and an on-off ratio of 10⁷ , which were obtained at 1 mol% In₂O₃ NCs in amorphous IZO films. Our findings demonstrate the feasibility of low-temperature sol-gel-based oxide semiconductor transistors, which is more cost-effective compared with conventional fabrication techniques but with comparable performance.

\hbox{Oxide/In}_{2}\hbox{O}_{3}

Two-dimensional layered materials have attracted significant interest for their potential applications in electronic and optoelectronics devices. Among them, transition metal dichalcogenides (TMDs), especially molybdenum disulfide (MoS2), is extensively studied because of its unique properties. Monolayer MoS2 so far can be obtained by mechanical exfoliation or chemical vapor deposition (CVD). However, controllable synthesis of large area monolayer MoS2 with high quality needs to be improved and their growth mechanism requires more studies. Here we report a systematical study on controlled synthesis of high-quality monolayer MoS2 single crystals using low pressure CVD. Large-size monolayer MoS2 triangles with an edge length up to 405 μm were successfully synthesized. The Raman and photoluminescence spectroscopy studies indicate high homogenous optical characteristic of the synthesized monolayer MoS2 triangles. The transmission electron microscopy results demonstrate that monolayer MoS2 triangles are single crystals. The back-gated field effect transistors (FETs) fabricated using the as-grown monolayer MoS2 show typical n-type semiconductor behaviors with carrier mobility up to 21.8 cm2 V−1 s−1, indicating excellent electronic property comparing with previously reported CVD grown MoS2 monolayer. The MoS2 FETs also show a high photoresponsivity of 7 A W−1, as well as a fast photo-response time of 20 ms. The improved synthesis method recommended here, which makes material preparation much easier, may strongly promote further research and potential applications.摘要二维层状材料由于其在光电器件方面的潜在应用引起了广泛关注, 二硫化钼(MoS2)是其中研究最多的材料之一. 单层二硫化钼可通过机械剥离或者化学气相合成的方法制备, 但是与石墨烯相比, 大面积且高质量的单层二硫化钼单晶的可控合成仍然有待提高. 本文报道了一种可控合成大面积高质量单层MoS2单晶的方法, 合成出了边长达405 μm的单层二硫化钼三角形. 对产物进行了光谱表征, 结果表明其光学性质十分均匀, 透射电镜表征结果表明产物是单晶结构. 基于单层MoS2的场效应晶体管(FET)表现出良好的电学性能, 其载流子迁移率高达21.8 cm2 V−1 s−1,光响应度为7 A W−1, 响应时间仅为20 ms. 此合成方法使单层MoS2的制备更加简易可靠, 可促进其进一步研究及应用.

Nanocrystal Hybrid Thin-Film Transistor

Here we report the fabrication and characterization of high mobility amorphous ZnMgO/single-walled carbon nanotube composite thin film transistors (TFTs) with a tunable threshold voltage. By controlling the ratio of MgO, ZnO and carbon nanotubes, high performance composite TFTs can be obtained with a field-effect mobility of up to 135 cm(2) V(-1) s(-1), a low threshold voltage of 1 V and a subthreshold swing as small as 200 mV per decade, making it a promising new solution-processed material for high performance functional circuits. A low voltage inverter is demonstrated with a functional frequency exceeding 5 kHz, which is only limited by parasitic capacitance rather than the intrinsic material speed. The overall device performance of the composite TFTs greatly surpasses not only that of the solution-processed TFTs, but also that of the conventional amorphous or polycrystalline silicon TFTs. It therefore has the potential to open up a new avenue to high-performance, solution-processed flexible electronics which could significantly impact the existing applications, and enable a whole new generation of flexible, wearable, or disposable electronics.