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Among other new device concepts, nickel silicide (NiSix)-based Schottky barrier nanowire transistors are projected to supplement down-scaling of the complementary metal-oxide-semiconductor (CMOS) technology as its physical limits are reached. Control over the NiSix phase and its intrusions into the nanowire are essential for superior performance and down-scaling of these devices. Several works have shown control over the phase, but control over the intrusion lengths has remained a challenge. To overcome this, we report a novel millisecond-range flash-lamp-annealing (FLA)-based silicidation process. Nanowires are fabricated on silicon-on-insulator substrates using a top-down approach. Subsequently, Ni silicidation experiments are carried out using FLA. It is demonstrated that this silicidation process gives unprecedented control over the silicide intrusions. Scanning electron microscopy and high-resolution transmission electron microscopy are performed for structural characterization of the silicide. FLA temperatures are estimated with the help of simulations.

Here, we report the observation of negative photoconductance (NPC) effect in highly arsenic-doped germanium nanowires (Ge NWs) for the infrared light. NPC was studied by light-assisted Kelvin probe force microscopy, which shows the depletion of carriers in n-Ge NWs in the presence of infrared light. The trapping of photocarriers leads to high recombination of carriers in the presence of light, which is dominant in the n-type devices. Furthermore, a carrier trapping model was used to investigate the trapping and detrapping phenomena and it was observed that the NPC in n-Ge occurred, because of the fast trapping of mobile charge carriers by interfacial states. The performance of n-type devices was compared with p-type NW detectors, which shows the conventional positive photoconductive behavior with high gain of 104. The observed results can be used to study the application of Ge NWs for various optoelectronic applications involving light tunable memory device applications.

This paper describes molecular layer doping of Ge nanowires. Molecules containing dopant atoms are chemically bound to a germanium surface. Subsequent annealing enables the dopant atoms from the surface bound molecules to diffuse into the underlying substrate. Electrical and material characterization was carried out, including an assessment of the Ge surface, carrier concentrations and crystal quality. Significantly, the intrinsic resistance of Ge nanowires with widths down to 30 nm, doped using MLD, was found to decrease by several orders of magnitude.

A laboratory measurement of the α -decay half-life of 190 Pt has been performed using a low background Frisch grid ionisation chamber. A total amount of 216.60(17) mg of natural platinum has been measured for 75.9 days. The resulting half-life is ( 4.97 ± 0.16 ) × 10 11 years , with a total uncertainty of 3.2%. This number is in good agreement with the half-life obtained using the geological comparison method.

This article presents a review of various methods for extracting the key parameters of junctionless (JL) MOSFETs, namely, the threshold voltage, flat-band voltage, doping concentration, carrier mobility, and parasitic series resistance. The applicability and limitations of different methods are analyzed using numerical simulations and experimental data for planar and tri-gate nanowire JL transistors with various nanowire widths.

The transport properties of novel device architectures depend strongly on the morphology and the quality of the interface between contact and channel materials. In silicon nanowires with nickel silicide contacts, NiSi 2–Si interfaces are particularly important as NiSi 2 is often found as the phase adjacent to the silicide–silicon interface during and after the silicidation. The interface orientation of these NiSi 2–Si interfaces as well as the ability to create abrupt and flat interfaces, ultimately with atomic sharpness, is essential for the properties of diverse emerging device concepts. We present a combined experimental and theoretical study on NiSi 2–Si interfaces. Interfaces in silicon nanowires were fabricated using silicidation and characterized by high-resolution (scanning) transmission electron microscopy. It is found that {111} interfaces occur in ⟨110⟩ nanowires. A tilted interface and an arrow-shaped interface are observed, which depends on the nanowire diameter. We have further modeled NiSi 2–Si interfaces by density functional theory. Different crystallographic orientations and interface variations, e.g., due to interface reconstruction, are compared with respect to interface energy densities. The {111} interface is energetically most favorable, which explains the experimental observations. Possible ways to control the interface type are discussed.

Films of self assembled diblock copolymers (BCPs) have attracted significant attention for generating semiconductor nanoarrays of sizes below 100 nm through a simple low cost approach for device fabrication. A challenging abstract is controlling microdomain orientation and ordering dictated by complex interplay of surface energies, polymer–solvent interactions and domain spacing. In context, microphase separated poly (styrene-b-ethylene oxide) (PS-b-PEO) thin films is illustrated to fabricate nanopatterns on silicon and germanium materials trenches. The trenched templates was produced by simple electron beam lithography using hydrogen silsesquioxane (HSQ) resist. The orientation of PEO, minority cylinder forming block, was controlled by controlling trench width and varying solvent annealing parameters viz. temperature, time etc. A noticeable difference in microdomain orientation was observed for Si and Ge trenches processed under same conditions. The Ge trenches promoted horizontal orientations compared to Si due to difference in surface properties without any prior surface treatments. This methodology allows to create Ge nanopatterns for device fabrication since native oxides on Ge often induce patterning challenges. Subsequently, a selective metal inclusion method was used to form hardmask nanoarrays to pattern transfer into those substrates through dry etching. The hardmask allows to create good fidelity, low line edge roughness (LER) materials nanopatterns.

The semiconductor industry has already entered the sub-10 nm region, which has led to the development of cutting-edge fabrication tools. However, there are other factors that hinder the best outcome of these tools, such as the substrate and resist materials, pre- and postfabrication processes, etc. Among the lithography techniques, electron beam lithography (EBL) is the prime choice when a job requires dimensions lower than 10–20 nm, since it can easily achieve such critical dimensions in reasonable time and effort. When obtaining pattern features in single nanometer regime, the resist material properties play an important role in determining the size. With this agenda in mind, many resists have been developed over the years suitable for attaining required resolution in lesser EBL writing time. This review article addresses the recent advancements made in EBL resists technology. It first describes the different lithography processes briefly and then progresses on to the parameters affecting the EBL fabrications processes. EBL resists are then bifurcated into their “family types” depending on their chemical composition. Each family describes one or two examples of the new resists, and their chemical formulation, contrast-sensitivity values, and highest resolution are described. The review finally gives an account of various alternate next-generation lithography techniques, promising dimensions in the nanometer range.

The complex physics of the interaction between short-pulse ultrahigh-intensity lasers and solids is so far difficult to access experimentally, and the development of compact laser-based next-generation secondary radiation sources, e.g., for tumor therapy, laboratory astrophysics, and fusion, is hindered by the lack of diagnostic capabilities to probe the complex electron dynamics and competing instabilities. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small-angle x-ray scattering of femtosecond x-ray free-electron laser pulses facilitates new capabilities for direct in situ characterization of intense short-pulse laser-plasma interactions at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short-pulse high-intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the preinscribed grating, due to plasma expansion. The density maxima are interleaved, forming a double frequency grating in x-ray free-electron laser projection for a short time, which is a hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets.

Ge-on-Si and Ge-on-insulator (GeOI) are the most promising materials for the next-generation nanoelectronics that can be fully integrated with silicon technology. To this day, the fabrication of Ge-based transistors with a n-type channel doping above 5 × 1019 cm−3 remains challenging. Here, we report on n-type doping of Ge beyond the equilibrium solubility limit (ne ≈ 6 × 1020 cm−3) together with a nanoscale technique to inspect the dopant distribution in n++-p junctions in GeOI. The n++ layer in Ge is realized by P+ ion implantation followed by millisecond-flashlamp annealing. The electron concentration is found to be three times higher than the equilibrium solid solubility limit of P in Ge determined at 800 °C. The millisecond-flashlamp annealing process is used for the electrical activation of the implanted P dopant and to fully suppress its diffusion. The study of the P activation and distribution in implanted GeOI relies on the combination of Raman spectroscopy, conductive atomic force microscopy, and secondary ion mass spectrometry. The linear dependence between the Fano asymmetry parameter q and the active carrier concentration makes Raman spectroscopy a powerful tool to study the electrical properties of semiconductors. We also demonstrate the high electrical activation efficiency together with the formation of ohmic contacts through Ni germanidation via a single-step flashlamp annealing process.Ge-on-Si and Ge-on-insulator (GeOI) are the most promising materials for the next-generation nanoelectronics that can be fully integrated with silicon technology. To this day, the fabrication of Ge-based transistors with a n-type channel doping above 5 × 1019 cm−3 remains challenging. Here, we report on n-type doping of Ge beyond the equilibrium solubility limit (ne ≈ 6 × 1020 cm−3) together with a nanoscale technique to inspect the dopant distribution in n++-p junctions in GeOI. The n++ layer in Ge is realized by P+ ion implantation followed by millisecond-flashlamp annealing. The electron concentration is found to be three times higher than the equilibrium solid solubility limit of P in Ge determined at 800 °C. The millisecond-flashlamp annealing process is used for the electrical activation of the implanted P dopant and to fully suppress its diffusion. The study of the P activation and distribution in implanted GeOI relies on the combination of Raman spectroscopy, conductive atomic force microscopy, an...

A method for cross-sectional doping of individual Si/SiO2 core/shell nanowires (NWs) is presented. P and B atoms are laterally implanted at different depths in the Si core. The healing of the implantation-related damage together with the electrical activation of the dopants takes place via solid phase epitaxy driven by millisecond-range flash lamp annealing. Electrical measurements through a bevel formed along the NW enabled us to demonstrate the concurrent formation of n- and p-type regions in individual Si/SiO2 core/shell NWs. These results might pave the way for ion beam doping of nanostructured semiconductors produced by using either top-down or bottom-up approaches.

Hyperdoping consists of the intentional introduction of deep-level dopants into a semiconductor in excess of equilibrium concentrations. This causes a broadening of dopant energy levels into an intermediate band between the valence and conduction bands.[1,2] Recently, bulk Si hyperdoped with chalcogens or transition metals has been demonstrated to be an appropriate intermediate-band material for Si-based short-wavelength infrared photodetectors.[3-5] Intermediate-band nanowires could potentially be used instead of bulk materials to overcome the Shockley-Queisser limit and to improve efficiency in solar cells,[6-9] but fundamental scientific questions in hyperdoping Si nanowires require experimental verification. The development of a method for obtaining controlled hyperdoping levels at the nanoscale concomitant with the electrical activation of dopants is, therefore, vital to understanding these issues. Here, we show a CMOS-compatible technique based on non-equilibrium processing for the controlled doping of Si at the nanoscale with dopant concentrations several orders of magnitude greater than the equilibrium solid solubility. Through the nanoscale spatially controlled implantation of dopants, and a bottom-up template-assisted solid phase recrystallization of the nanowires with the use of millisecond-flash lamp annealing, we form Se-hyperdoped Si/SiO2 core/shell nanowires that have a room-temperature sub-band gap optoelectronic photoresponse when configured as a photoconductor device.

Top-down fabrication of sub-50nm silicon nanowire sensors with various geometries.Excellent performance as backgated junctionless nanowire transistors (JNTs).Very good sensing capabilities.Among the smallest top-down fabricated nanowire sensing devices reported to date. This article reports the fabrication of sub-50nm field effect transistor (FET)-type silicon (Si) nanowire (Si NW) chemical and biological sensing devices with a junctionless architecture, as well as on the initial characterisation of their electrical and sensing performance.The devices were fabricated using a fully complementary metal-oxide-semiconductor (CMOS)-compatible top-down process on silicon-on-insulator (SOI) wafers. The fabrication process was mainly based on high-resolution electron beam lithography (EBL) and reactive ion etching (RIE) but also included photolithography (mix-and-match lithography), thin film deposition by electron beam evaporation, lift-off, thermal annealing and wet etching.The sensing performance of a matrix of nanowire devices, i.e. containing 1, 3 and 20 NWs with lengths of 0.5, 1 and 10µm was examined. Each element of the matrix also contained five devices with different NW widths: 10, 20, 30, and 50nm and 5µm (a Si belt reference device). Electrical characterisation of the devices showed excellent performance as backgated junctionless nanowire transistors (JNTs): high on-currents in the range of 1-10µA and high ratios between the on-state and off-state currents (Ion/Ioff) of 6-7 orders of magnitude. In addition, the results of ionic strength sensing experiments demonstrate the very good sensing capabilities of these devices. To the best of our knowledge, these nanowire sensors are among the smallest top-down fabricated Si NW devices reported to date.

A 3D, vertically stacked silicon nanowire (SiNW) field effect transistor (FET) featuring a high density array (7×20) of fully depleted channels has been successfully fabricated by a CMOS compatible process on silicon on insulator (SOI) and functionalized for streptavidin detection for the first time. The channels are surrounded by conformal high-κ gate dielectrics (HfO2), and their conductivity can be uniquely tuned by three gates; a backgate (BG) and two symmetrical Pt side gates (SG) through a liquid, offering unique sensitivity tuning with high gate coupling (SS=75 mV/dec, α'=SS60mV/dec/SSmeasured=0.8, with highest sensitivity=93-99%, obtained for I=1 0pA-10nA, in weak inversion) ever published.

A micro-power energy harvesting system based on core(crystalline Si)-shell(amorphous Si) nanowire solar cells together with a nanowire-modified CMOS sensing platform have been developed to be used in a dust-sized autonomous chemical sensor node. The mote (SiNAPS) is augmented by low-power electronics for power management and sensor interfacing, on a chip area of 0.25mm(2). Direct charging of the target battery (e. g., NiMH microbattery) is achieved with end-to-end efficiencies up to 90% at AM1.5 illumination and 80% under 100 times reduced intensity. This requires matching the voltages of the photovoltaic module and the battery circumventing maximum power point tracking. Single solar cells show efficiencies up to 10% under AM1.5 illumination and open circuit voltages, Voc, of 450-500mV. To match the battery's voltage the miniaturised solar cells (similar to 1mm(2) area) are connected in series via wire bonding. The chemical sensor platform (mm 2 area) is set up to detect hydrogen gas concentration in the low ppm range and over a broad temperature range using a low power sensing interface circuit. Using Telran TZ1053 radio to send one sample measurement of both temperature and H-2 concentration every 15 seconds, the average and active power consumption for the SiNAPS mote are less than 350nW and 2.1 mu W respectively. Low-power miniaturised chemical sensors of liquid analytes through microfluidic delivery to silicon nanowires are also presented. These components demonstrate the potential of further miniaturization and application of sensor nodes beyond the typical physical sensors, and are enabled by the nanowire materials platform.

Germanium is a promising high-mobility channel material for future nanoelectronic devices. Hydrogen silsesquioxane (HSQ) is a well known high-resolution electron beam lithography (EBL) resist, which is usually developed in aqueous based developers. However, this feature of HSQ causes troubles while patterning Ge surface as it is always shielded with native Ge oxides. GeO2 is a water soluble oxide, and since HSQ resist is developed in aqueous solvents, this oxide interferes with the patterning. After the EBL exposure, GeO2 is washed off during the development, lifting the patterned structures and making the high-resolution patterning impossible. To avoid this issue, it is necessary to either clean and passivate the Ge surface or use buffer layers between the native Ge oxides and the HSQ layer. In this article, a novel technique to clean the Ge surface prior to HSQ deposition, using simple “household” acids like citric acid and acetic acid, is reported. The acids are able to remove the native Ge oxides as w...

Silicon nanowire (SiNW) field effect transistors (FETs) have been widely investigated as biological sensors for their remarkable sensitivity due to their large surface to volume ratio (S/V) and high selectivity towards a myriad of analytes through functionalization. In this work, we propose a long channel (L > 500 nm) junctionless nanowire transistor (JNT) SiNW sensor based on a highly doped, ultrathin body field-effect transistor with an organic gate dielectric epsilon(r) = 1.7. The operation regime (threshold voltage V-th) and electrical characteristics of JNTs can be directly tuned by the careful design of the NW/Fin FET. JNTs are investigated through 3D Technology Computer Aided Design (TCAD) simulations performed as a function of geometrical dimensions and channel doping concentration N-d for a p-type tri-gated structure. Two different materials, namely, an oxide and an organic monolayer, with varying dielectric constants er provide surface passivation. Mildly doped N-d = 1 x 10(19) cm(-3), thin bodied structures (fin width F-w < 20 nm) with an organic dielectric (epsilon(r) = 1.7) were found to have promising electrical characteristics for FET sensor structures such as V-th similar to 0 V, high relative sensitivities in the subthreshold regime S > 95%, high transconductance values at threshold g(m),(Vfg=0V) > 10 nS, low subthreshold slopes SS similar to 60 mV/dec, high saturation currents I-d,I-max similar to 1-10 mu A and high I-on/I-off > 10(4)-10(10) ratios. Our results provide useful guidelines for the design of junctionless FET nanowire sensors that can be integrated into miniaturized, low power biosensing systems. (c) 2013 Elsevier B.V. All rights reserved.

Silicon nanowire (Si NW) sensors have attracted great attention due to their ability to provide fast, low-cost, label-free, real-time detection of chemical and biological species. Usually configured as field effect transistors (FETs), they have already demonstrated remarkable sensitivity with high selectivity (through appropriate functionalisation) towards a large number of analytes in both liquid and gas phases. Despite these excellent results, Si NW FET sensors have not yet been successfully employed to detect single molecules of either a chemical or biological target species. Here we show that sensors based on silicon junctionless nanowire transistors (JNTs), the simplest possible transistors, are capable of detecting the protein streptavidin at a concentration as low as 580 zM closely approaching the single molecule level. This ultrahigh detection sensitivity is due to the intrinsic advantages of junctionless devices over conventional FETs. Apart from their superior functionality, JNTs are much easier to fabricate by standard microelectronic processes than transistors containing p–n junctions. The ability of JNT sensors to detect ultra-low concentrations (in the zeptomolar range) of target species, and their potential for low-cost mass production, will permit their deployment in numerous environments, including life sciences, biotechnology, medicine, pharmacology, product safety, environmental monitoring and security.