Single Nanowire Field Effect Transistors Research Articles

High-Transconductance and Low-Leakage Current Single Aluminum Nitride Nanowire Field Effect Transistor

This study presents electrical transport properties of a catalyst-free grown single aluminum nitride nanowire field effect transistor (AlNNW-FET) exhibiting a very high transconductance of 26.9 pS, high on/off current ratio of 795.9, high conductivity of 9.8 x 10-4 Ω-1.cm-1, and a very low leakage current of 10 pA. The conductivity of AlN nanowire is two orders of magnitude higher than the reported studies. The AlNNW-FET reveals a dominant p-type conductivity. The p-type conductivity can be attributed to aluminum vacancies and complexes composed of Al vacancies and oxygen impurities. In consequence, the fabricated AlNNW-FET with high-performance, cost-effectiveness, and high-power efficiency is very well suited for use in low power and high temperature nanoelectronic and piezoelectric sensor applications, as well as integrated electro-optical devices including optomechanical devices and pyroelectric photodetectors.

Growth of PbTe nanowires by molecular beam epitaxy

Advances in quantum technology may come from the discovery of new materials systems that improve the performance or allow for new functionality in electronic devices. Lead telluride (PbTe) is a member of the group IV–VI materials family that has significant untapped potential for exploration. Due to its high electron mobility, strong spin–orbit coupling and ultrahigh dielectric constant it can host few-electron quantum dots and ballistic quantum wires with opportunities for control of electron spins and other quantum degrees of freedom. Here, we report the fabrication of PbTe nanowires by molecular beam epitaxy. We achieve defect-free single crystalline PbTe with large aspect ratios up to 50 suitable for quantum devices. Furthermore, by fabricating a single nanowire field effect transistor, we attain bipolar transport, extract the bandgap and observe Fabry–Pérot oscillations of conductance, a signature of quasiballistic transmission.

Electrical properties of a single Ni-contact SnO2 nanowire field-effect transistors

Single crystalline SnO2 nanowires were grown using chemical vapor deposition (CVD) method and fabricated into a single-nanowire field-effect transistor (FET) with Ni contact electrodes by photolithography. Investigations show good field-effect electrical performance was achieved using the Ni-contact single-SnO2 nanowire device. Field effect mobility, on/off ratio and carrier species were 73.3 ± 4.17 cm2/V-s (for 10 devices), ~106, and electrons, respectively. Furthermore, a low barrier height of 45.6 meV between the Ni contact and as-grown SnO2 nanowire was achieved based on temperature dependent current-voltage measurement. It is thought this low barrier height improved field-effect transistor performance making SnO2 nanomaterial devices practicable.

Transport Characteristics of Gallium Nitride Nanowire Field-Effect Transistor (GaN-NWFET) for High Temperature Electronics

This paper presents a systematic investigation of high-temperature transport characteristics of a single nanowire Gallium Nitride nanowire field-effect transistor (GaN-NWFET) ranging from room temperature to as high as [Formula: see text]C for the first time. The GaN-NWFET demonstrated a very good on/off current ratio ([Formula: see text] of [Formula: see text] for the p-side and [Formula: see text] for the n-side at room temperature and considerably well at high temperatures. In fact, the device exhibited an on/off current ratio of [Formula: see text] and a transconductance value of [Formula: see text]S for the p-side at [Formula: see text]C indicating a good gating effect even at high temperatures. Additionally, the device exhibited very high mobilities with the hole mobility of [Formula: see text][Formula: see text]cm2/V. s and electron mobility of [Formula: see text] cm2/V. s at room temperature. Furthermore, the device showed very high transconductance values of [Formula: see text]S and [Formula: see text]S at the temperatures of [Formula: see text]C and [Formula: see text]C, respectively. As a consequence, the GaN-NWFET devices could find much use not only in high-power, but also in low-power transistor applications beyond the ambient temperature [Formula: see text]C) of silicon and silicon-on-insulator technologies for electronic and photonic circuits.

Fabrication of Vertically Stacked Nanosheet Junctionless Field-Effect Transistors and Applications for the CMOS and CFET Inverters

In this study, conventional CMOS and complementary field-effect transistor (CFET) inverters based on a vertically stacked-nanosheet (NS) structure were fabricated. The NS below 8-nm channel layer thickness ( ${T}_{{\text {Si}}}$ ) was obtained by dry etching and wet etching processes. The channel thickness is controlled by dry etching, and the channel width was shrunk down by wet etching. Compared to single nanowire field-effect transistors (NSFETs), stacked NSFETs exhibit higher ON-current performance. For the CMOS inverter, the voltage transfer characteristics (VTCs) could be matched much better by adjusting the channel widths and layers for N-channel MOSFET (NFET) and P-channel MOSFET (PFET), respectively. For the CFET inverter, layout areas could be reduced and requires less number of lithographic and ion implantation steps contrary to the CMOS inverter. However, we observe that the VTCs of the CFET inverters still show asymmetric behavior due to the difficulties of adjustment in NS layers and systematic behavior of threshold voltages for NFETs/PFETs. This work experimentally demonstrates the CMOS and CFET inverters on the vertically stacked NS structure, which is promising for system-on-panel (SoP) and 3-D-ICs applications.

Enhanced conductivity of anatase TiO 2 nanowires by La and Co co‐doping

In this work, the conductivity of anatase titanium dioxide (TiO2) nanowires was enhanced by lanthanum (La) and cobalt (Co) co-doping method. The nanowires were synthesised via a facile solvothermal process. The diameter of as-synthesised nanowires is about 300 nm and length more than 20 μm. The electrical properties were studied based on single nanowire field-effect transistor; the anatase TiO2 nanowires exhibit n-type conductivity with mobility of 2.18 cm2 V−1 S−1 and carrier concentration of 1.95 × 1018 cm−3. Doping of rare earth element La and transition element Co can not only reduce bandgap, but also reduce electron–hole recombination and improve carrier concentration. The distinct electrical properties of doped nanowires will open new opportunities for the application of anatase TiO2 semiconductor materials in nanoelectronics devices.

Fingerprinting Electronic Structure in Nanomaterials: A Methodology Illustrated by ZnSe Nanowires.

Characterizing point defects that produce deep states in nanostructures is imperative when designing next-generation electronic and optoelectronic devices. Light emission and carrier transport properties are strongly influenced by the energy position and concentration of such states. The primary objective of this work is to fingerprint the electronic structure by characterizing the deep levels using a combined optical and electronic characterization, considering ZnSe nanowires as an example. Specifically, we use low temperature photoluminescence spectroscopy to identify the dominant recombination mechanisms and determine the total defect concentration. The carrier concentration and mobility are then calculated from electron transport measurements using single nanowire field effect transistors, and the measured experimental data were used to construct a model describing the types, energies, and ionized fraction of defects and calculate the deviation from stoichiometry. This metrology is hence demonstrated to provide an unambiguous means to determine a material's electronic structure.

Field effect transistors and phototransistors based upon p-type solution-processed PbS nanowires

We demonstrate the fabrication of solution processed highly crystalline p-type PbS nanowires via the oriented attachment of nanoparticles. The analysis of single nanowire field effect transistor (FET) devices revealed a hole conduction behaviour with average mobilities greater than 30 cm2 V−1 s−1, which is an order of magnitude higher than that reported to date for p-type PbS colloidal nanowires. We have investigated the response of the FETs to near-infrared light excitation and show herein that the nanowires exhibited gate-dependent photo-conductivities, enabling us to tune the device performances. The responsivity was found to be greater than 104 A W−1 together with a detectivity of 1013 Jones, which benefits from a photogating effect occurring at negative gate voltages. These encouraging detection parameters are accompanied by relatively short switching times of 15 ms at positive gate voltages, resulting from a combination of the standard photoconduction and the high crystallinity of the nanowires. Collectively, these results indicate that solution-processed PbS nanowires are promising nanomaterials for infrared photodetectors as well as p-type nanowire FETs.

A facile hydrothermal approach for the density tunable growth of ZnO nanowires and their electrical characterizations

Controlling properties of one-dimensional (1D) semiconducting nanostructures is essential for the advancement of electronic devices. In this work, we present a low-temperature hydrothermal growth process enabling density control of aligned high aspect ratio ZnO nanowires (NWs) on seedless Au surface. A two order of magnitude change in ZnO NW density is demonstrated via careful control of the ammonium hydroxide concentration (NH4OH) in the solution. Based on the experimental observations, we further, hypothesized the growth mechanism leading to the density controlled growth of ZnO NWs. Moreover, the effect of NH4OH on the electrical properties of ZnO NWs, such as doping and field-effect mobility, is thoroughly investigated by fabricating single nanowire field-effect transistors. The electrical study shows the increase of free charge density while decrease of mobility in ZnO NWs with the increase of NH4OH concentration in the growth solution. These findings show that NH4OH can be used for simultaneous tuning of the NW density and electrical properties of the ZnO NWs grown by hydrothermal approach. The present work will guide the engineers and researchers to produce low-temperature density controlled aligned 1D ZnO NWs over wide range of substrates, including plastics, with tunable electrical properties.

Fabrication of single Ga-doped ZnS nanowires as high-gain photosensors by focused ion beam deposition

ZnS nanowires were synthesized via a vapor–liquid–solid mechanism and then fabricated into a single-nanowire field-effect transistor by focused ion beam (FIB) deposition. The field-effect electrical properties of the FIB-fabricated ZnS nanowire device, namely conductivity, mobility and hole concentration, were 9.13 Ω−1 cm−1, 13.14 cm2 V−1 s−1and 4.27 × 1018 cm−3, respectively. The photoresponse properties of the ZnS nanowires were studied and the current responsivity, current gain, response time and recovery time were 4.97 × 106 A W−1, 2.43 × 107, 9 s and 24 s, respectively. Temperature-dependent I–V measurements were used to analyze the interfacial barrier height between ZnS and the FIB-deposited Pt electrode. The results show that the interfacial barrier height is as low as 40 meV. The energy-dispersive spectrometer elemental line scan shows the influence of Ga ions on the ZnS nanowire surface on the FIB-deposited Pt contact electrodes. The results of temperature-dependent I–V measurements and the elemental line scan indicate that Ga ions were doped into the ZnS nanowire, reducing the barrier height between the FIB-deposited Pt electrodes and the single ZnS nanowire. The small barrier height results in the FIB-fabricated ZnS nanowire device acting as a high-gain photosensor.

Controllable gas selectivity at room temperature based on Ph5T2-modified CuPc nanowire field-effect transistors

A dinaphtho[3,4-d:3′,4′-d′]benzo[1,2-b:4,5-b′]dithiophene (Ph5T2)-modified copper phthalocyanine (CuPc) single crystal nanowire field-effect transistor (FET) with gas dielectric was fabricated as an organic gas sensor. This device exhibits the high response and the excellent controllable selectivity at room temperature. Its detection limit for NO2, NO, and H2S is down to sub-ppm level. Prior to surface modification, the CuPc nanowire FET shows the response as high as 1088% to 10 ppm H2S, but only 97.5% to 10 ppm NO2. After Ph5T2 modification, the response to 10 ppm H2S is decreased by one order of magnitude, but is dramatically improved up to 460% to 10 ppm NO2. The responses towards H2S and NO2 respectively for pristine and the modified sensor are higher than those of most reported organic sensors. The gas-sensing results reveal that Ph5T2 modification can transform the selectivity of the sensor from H2S to NO2. The controllable modulation of gas selectivity is related to the formed organic heterojunctions between CuPc and Ph5T2, where the hole carriers of CuPc nanowire are modulated by these heterojunctions, resulting in the changed adsorption behavior towards different gases.

Manipulation of Optoelectronic Properties and Band Structure Engineering of Ultrathin Te Nanowires by Chemical Adsorption.

Band structure engineering is a powerful technique both for the design of new semiconductor materials and for imparting new functionalities to existing ones. In this article, we present a novel and versatile technique to achieve this by surface adsorption on low dimensional systems. As a specific example, we demonstrate, through detailed experiments and ab initio simulations, the controlled modification of band structure in ultrathin Te nanowires due to NO2 adsorption. Measurements of the temperature dependence of resistivity of single ultrathin Te nanowire field-effect transistor (FET) devices exposed to increasing amounts of NO2 reveal a gradual transition from a semiconducting to a metallic state. Gradual quenching of vibrational Raman modes of Te with increasing concentration of NO2 supports the appearance of a metallic state in NO2 adsorbed Te. Ab initio simulations attribute these observations to the appearance of midgap states in NO2 adsorbed Te nanowires. Our results provide fundamental insights into the effects of ambient on the electronic structures of low-dimensional materials and can be exploited for designing novel chemical sensors.

Gate-controlled heat generation in ZnO nanowire FETs.

Nanoscale heating production using nanowires has been shown to be particularly attractive for a number of applications including nanostructure growth, localized doping, transparent heating and sensing. However, all proof-of-concept devices proposed so far relied on the use of highly conductive nanomaterials, typically metals or highly doped semiconductors. In this article, we demonstrate a novel nanoheater architecture based on a single semiconductor nanowire field-effect transistor (NW-FET). Nominally undoped ZnO nanowires were incorporated into three-terminal devices whereby control of the nanowire temperature at a given source-drain bias was achieved by additional charge carriers capacitatively induced via the third gate electrode. Joule-heating selective ablation of poly(methyl methacrylate) deposited on ZnO nanowires was shown, demonstrating the ability of the proposed NW-FET configuration to enhance by more than one order of magnitude the temperature of a ZnO nanowire, compared to traditional two-terminal configurations. These findings demonstrate the potential of field-effect architectures to improve Joule heating power in nanowires, thus vastly expanding the range of suitable materials and applications for nanowire-based nanoheaters.

Fabrication of field-effect transistors and functional nanogenerators using hydrothermally grown ZnO nanowires

We demonstrate single crystalline ZnO nanowire (NW) production using hydrothermal process. Single NW field-effect transistors (FETs) and functional piezoelectric nanogenerators (NGs) are demonstrated by thermal annealing of the NWs in air at ~450 °C.

Electrical transport and photoresponse properties of single-crystalline p-type Cd3As2 nanowires

Cd3As2 is an important II–V group semiconductor with excellent electrical and optoelectronic properties. In this work, we report the large scale growth of single-crystalline Cd3As2 nanowires via a simple chemical vapor deposition method. Single nanowire field-effect transistors were fabricated with the as-grown Cd3As2 nanowires, which exhibited a high I on/I off of 104 with a hole mobility of 6.02 cm2V−1s−1. Photoresponse properties of the Cd3As2 nanowires were also investigated by illuminating the nanowires with white light by varying intensities. Besides, flexible photodetectors were also fabricated on flexible PET substrate, showing excellent mechanical stablility and flexible electro-optical properties under various bending states and bending cycles. Our results indicate that Cd3As2 nanowires can be the basic material of next generation electronic and optoelectronic devices.

Gate modulation of below-band-gap photoconductivity in ZnO nanowire field-effect-transistors

We investigated the modulation of the photoconductivity under below-band gap excitation in single ZnO nanowire field effect transistors. Light excitation at 550 nm does not induce any change in the drain–source current when the gate voltage is kept at Vgs = 0 V, but results in a current increase when it is set to Vgs = −50 V. At this negative value of the gate voltage we further investigated the photo-reaction in the below-band-gap range 400–800 nm, observing a qualitative similar profile for all the photo-current curves. These results were attributed to a local effect, suggesting that the change in conductivity is due to the release of electrons from interface states located between the ZnO nanowire active channel and the gate dielectric SiO2.

ZnO nanowire field-effect transistors with Pt nanocrystals fabricated on a flexible plastic substrate for a non-volatile memory application

In this work, a single ZnO nanowire field-effect transistor (NWFET) with discrete-trap storage nodes of Pt nanocrystals (NCs) embedded within Al2O3, a high-κ tunneling/control dielectric material, was successfully fabricated on a flexible plastic substrate for a non-volatile memory application. The ZnO NWFET with embedded Pt NCs exhibits a clear hysteresis loop with a threshold voltage shift of 4.16 V under the ±15 V gate–source voltage sweep ranges, implying that the charging and discharging phenomena occur during the program/erase operations. The ZnO NWFET achieves a reasonable value of approximately 105 for the on/off current ratio for read-out of storage data. Furthermore, memory features, such as programming efficiency and on-cell current, are compared between the flat and convexly bent states in order to investigate the feasibility of flexible plastic devices as transistors.

Catalyst-Free Heteroepitaxial MOCVD Growth of InAs Nanowires on Si Substrates

We report the systematic study of catalyst-free syntheses of InAs nanowires on Si substrates with various growth parameters and surface treatments. Nanowire morphology and crystal structure were studied using scanning electron microscopy and transmission electron microscopy. High-resolution cross-sectional transmission electron microscopy studies reveal heteroepitaxy of InAs[111] nanowires on Si(111) substrate with clean and sharp interface. Single nanowire field-effect transistor measurements of InAs nanowires under optimal growth conditions indicate a typical electron concentration of 1018–1019 cm–3 and mobility of around 1000 cm2/V·s. III/V on Si devices with InAs nanowire array on p-Si show a broadband photodetection up to wavelength of 3.5 μm.

Effect of indium concentration on luminescence and electrical properties of indium doped ZnO nanowires

In this work, indium (In) doped ZnO nanowires are grown on a Si substrate by chemical vapor deposition (CVD), at a relatively low temperature of 550°C. The effects of In concentration on the morphology, microstructure, luminescence and electrical properties of ZnO nanowires are investigated. The diameters and lengths of these nanowires are in the ranges of 70–311nm and 10–15μm, respectively. These nanowires are single crystals growing in the [0001] direction. The maximum solubility of In in ZnO is estimated to be 3.47at.%. Photoluminescence (PL) spectra reveal a red shift in the ultraviolet emission and intensity enhancement in the green emission with increasing indium doping concentration. Besides, carrier concentration, mobility and resistivity of the nanowires with different doping concentrations are determined based on single-nanowire field effect transistors (FET).

Growth and large-scale assembly of InAs/InP core/shell nanowire: effect of shell thickness on electrical characteristics

InAs/InP core/shell nanowires with different shell thicknesses were grown by a two-step method, and large-scale assembly of single nanowire was realized by using dielectrophoresis alignment and patterned grooves. Thousands of single nanowire field-effect transistors were fabricated on a single chip. The effect of InP shell thickness on the electron mobility and density of InAs nanowires are experimentally investigated and discussed.