Schottky diodes have been a fundamental component of electrical circuits for many decades, and intense research continues to this day on planar materials with increasingly exotic compounds. With the birth of nanotechnology, a paradigm shift occurred with Schottky contacts proving to be essential for enabling nanodevice inventions and increasing their performance by many orders of magnitude, particularly in the fields of piezotronics and piezoelectric energy harvesting. ZnO nanomaterials have proven to be the most popular materials in those devices as they possess high piezoelectric coefficients, high surface sensitivity, and low resistivity due to the high native n-type doping and low hole concentration. ZnO nanowires grown by vapor phase techniques with the aid of a metal catalyst provide a ready-made epitaxial Schottky contact free from interfacial layers and major defects. We show here with the most comprehensive experimental investigation to-date of Au nanocontacts to ZnO nanowires that the modulation of bulk and surface oxygen can dramatically increase the rectifying quality of these contacts when applied in the metal-semiconductor-metal (M-S-M) device configuration with potential barriers approaching the performance of planar contacts on single crystal ZnO. Before modification, the Au-ZnO nanowire contacts in a rectifying-nanowire-ohmic M-S-M device configuration typically show limited current rectification and electrical transport properties dominated by surface effects and tunneling at the contact edge. Interestingly, the oxygen modulation only has a minor effect on the resistivity as the high-resolution cathodoluminescence spectroscopy shows that the dominant donors are In, Ga, and Al with no visible band emissions often associated with detrimental point defects. The spectroscopy also revealed that carbon is incorporated into the bulk that may present interesting magnetic properties for future spintronics applications. Atomic-resolution electron microscopy confirms the Zn-polar orientation of the high-quality single crystal nanowires used for the electrical measurements. X-ray photoelectron spectroscopy shows oxygen-annealed nanowires have fewer surface oxygen defects, and when that difference is coupled with a reduction in surface oxygen vacancies via oxygen plasma treatment, the current rectification can increase by several orders of magnitude with a much lower dispersion in the effective potential barrier properties when compared to those that are not annealed. This study concludes after the electrical measurements of 66 nanowire contacts/M-S-M structures with diameters as small as 25 nm using a scanning tunneling microscopy probe that effective device potential barrier heights of 0.65 eV and on-off ratios of 3 orders of magnitude can be achieved. Interestingly, this change in contact properties is transient in nature, revealing dynamic surface effects can govern the rectifying behavior and surface passivation techniques are desirable to achieve consistent performance. This work shows the overriding effects of surface defects and adsorbates on the sloping facets near the Au contact edge and the potential for this effect to be used to control the electrical transport properties and produce molecular-scale sensors to greatly enhance the performance of many piezotronic and energy harvesting devices.

We demonstrate quasi-vertical GaN MOSFETs fabricated on SiC substrates. The GaN epitaxial layers were grown via MOCVD on 100 mm 4H-SiC wafers, with the device structure consisting of a 2.5 μm drift layer and a Mg doped p-GaN body. The fabricated transistors exhibit normally-off characteristics, with low off-state leakage behavior and an on/off ratio of over . The specific on-resistance was measured to be which compares favorably to devices fabricated on other foreign substrates. Our results demonstrate an alternative substrate for realizing vertical GaN devices, which potentially offers better material quality and thermal properties compared with other foreign substrate choices.

High‐quality, alumina thin films are extensively used as dielectrics, passivation layers, and barrier layers in electronics and many other applications. However, to achieve optimum stoichiometry and thus performance, the layers are often grown at elevated temperatures (>200 °C) using techniques such as atomic layer deposition (ALD). This is problematic for substrates or structures with low thermal budgets. Herein, alumina thin films are grown on 200 mm silicon substrates employing a versatile deposition method known as MVD at low deposition temperatures (35–150 °C). The chemical composition of the resulting films is investigated postdeposition using X‐ray photoelectron spectroscopy (XPS) and variable angle spectroscopic ellipsometry, with fully stoichiometric Al 2 O 3 achieved at deposition temperatures as low as 100 °C. Dielectric measurements confirm outstanding dielectric properties compared to typical thermal ALD layers deposited at much higher temperatures. This low‐temperature deposition performance by considering the MVD reactor design and the “pump‐type” regime of precursor delivery versus the “flow‐type” regime of ALD is rationalized and understood. The results clearly demonstrate that alumina thin films grown with MVD are highly versatile for electronic applications and are of particular relevance and interest for the high‐volume processing of dielectric, passivation, and barrier layers at low temperatures.

In this paper, a vertical device structure and its process flow are proposed for fabrication of Gallium Nitride Trench Field Effect Transistors (GaNTT). A TCAD model is developed to capture effect of bulk and interface traps on the electrical performance of fully vertical Gallium Nitride devices on a Silicon Carbide substrate (GaN-on-SiC). The simulation results show a promising specific on-resistance of Rsp,on = 1.4 mΩ . cm2 and a blocking voltage of BV = 540V at VGS=0V for a GaN drift thickness of 4 μm.

Affinity biosensors based on graphene field-effect transistor (GFET) or resistor designs require the utilization of graphene's exceptional electrical properties. Therefore, it is critical when designing these sensors, that the electrical properties of graphene are maintained throughout the functionalization process. To that end, non-covalent functionalization may be preferred over covalent modification. Drop-cast 1,5-diaminonaphthalene (DAN) was investigated as a quick and simple method for the non-covalent amine functionalization of carbon-based surfaces such as graphene, for use in biosensor development. In this work, multiple graphene surfaces were functionalized with DAN via a drop-cast method, leading to amine moieties, available for subsequent attachment to receptor molecules. Successful modification of graphene with DAN via a drop-cast method was confirmed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and real-time resistance measurements. Successful attachment of receptor molecules also confirmed using the aforementioned techniques. Furthermore, an investigation into the effect of sequential wash steps which are required in biosensor manufacture, on the presence of the DAN layer, confirmed that the functional layer was not removed, even after multiple solvent exposures. Drop-cast DAN is thus, a viable fast and robust method for the amine functionalization of graphene surfaces for use in biosensor development.

Herein, we present an experimental/computational approach for probing the interaction between metal contacts and carbon nanotubes (CNTs) with regard to creating the most efficient, low resistance junction. Tungsten probes have been coated with copper or chromium and the efficiency of nanocontact transport into multiwalled carbon nanotubes (MWCNTs) has been investigated experimentally, using scanning tunneling spectroscopy and nanoscale two-point probe I-V measurements, and in silico, employing DFT calculations. Experimental I-V measurements suggest the relative conductivity of the metal-CNT interaction to be Cu > W > Cr. It has been found that copper when in contact with MWCNTs results in a high density of states at the Fermi level, which contributes states to the conduction band. It was observed that the density of states also increased when chromium and tungsten probes were in contact with CNTs; however, in these cases the density of states increase would only occur under high voltage/high temperature situations. This is demonstrated by an increase in the experimental electrical resistance when compared to the copper probe. These results suggest that in future copper tips should be used when carrying out all intrinsic conduction measurements on CNTs, and they also provide a rationale for the ultraconductivity of Cu-CNT and Cu-graphene composites.

Semiconductor CMOS nano-electronics is intensively seeking solutions for future digital applications. One of the most promising solutions to deliver a technological breakthrough is exploring electron spin in metals and semiconductors with applications from spin transistors to quantum sensors, and quantum computing. Spintronic applications rely on magnetic semiconductor materials with suitable properties. In particular, dilute magnetic semiconductors (DMS), such as Mn doped GaN, show the great promise of a high Curie temperature (220K–370K), exceeding room temperature, and a large concentration of holes. These are all the essential pre-requisites for operation of spin transistors in circuits. In this work, we dope an AlGaN/GaN heterostructure consisting of a GaN (2 nm) cap layer, an Al0.25Ga0.75N (25 nm) barrier, and a GaN (2 μm) substrate grown on a 6” Si wafer with Mn by sputtering deposition and thermal annealing to create a dilute magnetic semiconductor material following the process flow. While initial attempts resulted in the formation of a MnO surface layer, the SEM/XDS and XPS data suggest a diffusion of Mn into the GaN layer using thermal annealing at 900◦C for 7h with a concentration of 4.5% which is very close to the desired concentration of 5% needed for a DMS. The annealing temperature has to be below 1000◦ C since temperatures around 1000◦C result in significant damage to the 2DEG and diffusion of Al from the AlGaN layer.

For the first time, we report on the superior performance of the dual-drain gallium nitride (GaN) magnetic field-effect transistor (MagFET) at elevated temperatures. The IV characteristics of the devices reported here were collected under dc conditions and tested at elevated temperatures, 300, 323, 373, and 448 K using a custom-made heating stage, with a thermal feedback loop to accurately control the temperature. Light exposure experiments were conducted during raised temperature levels using an LED light source of wavelength 470 nm. The relative sensitivity of the GaN dual-drain MagFET was calculated and demonstrated a degradation from 9.78% T-1 at 300 K to 8.36% T-1 at 323 K, 6.10% T-1 at 373 K, and 3.79% T-1 at 448 K. This is equal to a small sensitivity decrease of 0.04% T-1/K. It is proposed that the observed reduction in sensitivity reported herein is due to increased phonon scattering in the 2-D electron gas channel. Despite this reduced sensitivity at elevated temperatures, the lowest sensitivity measured at 448 K surpasses those reported for silicon competitors.

This letter presents first-ever fabricated GaN split-current magnetic sensor device. Device operation and key manufacturing steps are also presented. The measured relative current sensitivity is constant at 14 % T-1 for wide mT range of the magnetic field. Constant sensitivity of a fabricated sensor can be attributed to device's 2DEG nature, i.e., its high electron concentration and mobility, and very small layer thickness.

ZnO nanosheets are polycrystalline nanostructures that are used in devices including solar cells and gas sensors. However, for efficient and reproducible device operation and contact behaviour the conductivity characteristics must be controlled and surface contaminants removed. Here we use low doses of argon bombardment to remove surface contamination and make reproducible lower resistance contacts. Higher doses strip the surface of the nanosheets altering the contact type from near-ohmic to rectifying by removing the donor-type defects, which photoluminescence shows to be concentrated in the near-surface. Controlled doses of argon treatments allow nanosheets to be customised for device formation.

The three-dimensional simulations, calibration, measured currents and calculated relative sensitivities of the first-ever fabricated double-drain gallium nitride (GaN) magnetic field effect transistor (MagFET) are given in this work. The MagFETs are GaN high electron mobility transistors (HEMTs) capable of operating under harsh environments. Geometrical and operational analysis are carried out on MagFETs using commercial simulation software Silvaco. The analysis shows promising relative sensitivities of 6.84%T-1 and 5.04%T-1 at ambient temperatures of 400 K and 500 K, respectively. In addition, the relative sensitivity of fabricated device is improved from 12%T-1 to 24%T-1 at 300 K by optimising device geometrical parameters.

Near-term commercialization of nanowire-based devices is possible through an integrative approach with existing semiconductor platforms. Research-based single nanowire devices suffer from issues related to size dependence and variability; hence, the use of a large number of nanowires in parallel is a prerequisite for real-world devices to scale output and provide statistical averaging of properties. Parallel integration is most directly achieved through electrical contacting of nanowire arrays in the as-grown vertical configuration. Here, we demonstrate a one-step process that overcomes several technological barriers simultaneously, allowing the seamless electrical integration of ZnO nanowire arrays with industry standard silicon substrates. Our seamless integration process is based on the deposition of a metal contact layer on silicon and subsequent CVD nanowire growth. Combined SEM, XRD, and TEM measurements show compositional and structural changes to each metal contact layer candidate during the high-temperature growth process, directly influencing the ZnO base growth and controlling the properties and dimensions of the resulting nanowire arrays. Findings were correlated to nanoscale multiprobe electrical measurements of individual nanowires in the vertical device configuration to demonstrate the effects of each metal layer on conduction through the nanowires and the metal semiconductor interface. The refractory metal molybdenum gave highly aligned, dense nanowire growth and formed a low-resistance ohmic contact to the base of these arrays offering a simple and scalable process-ready solution for integrating nanowires with the industry standard silicon platform.

The application of electrical nanoprobes to measure and characterize nanomaterials has become widely spread. However, the formation of quality electrical contacts using metallic probes on nanostructures has not been directly assessed. We investigate here the electrical behaviour of non-lithographically formed contacts to ZnO nanowires (NWs) and develop a method to reproducibly form Ohmic contacts for accurate electrical measurement of the nanostructures. The contacting method used in this work relies on an electrical feedback mechanism to determine the point of contact to the individual NWs, ensuring minimal compressive strain at the contact. This developed method is compared with the standard tip deflection contacting technique and shows a significant improvement in reproducibility. The effect of excessive compressive strain at the contact was investigated, with a change from rectifying to ohmic I-V behaviour observed as compressive strain at the contact was increased, leading to irreversible changes to the electrical properties of the NW. This work provides an ideal method for forming reproducible nonlithographic nanocontacts to a multitude of nanomaterials.

•Arrays of catalyst-free ZnO NWs have been grown by CVD without seed layers on Si.•Si surface topography was altered by substrate etching, resulting in NW growth.•XPS analysis shows growth is related to topography and not surface contamination.•Using e-beam lithography with etching, selective nanowire growth is demonstrated.•Electrical measurements on the arrays show improved conduction through the Si.

The application of electrical nanoprobes to measure and characterise nanomaterials has become widely spread. However, the formation of quality electrical contacts using metallic probes on nanostructures has not been directly assessed. We investigate here the contact electrical behaviour of non-lithographically formed contacts to ZnO nanowires and develop a method to reproducibly form contacts. The contacting method NWs relies on an electrical feedback to determine the point of contact, ensuring minimal compressive strain at the contact. This developed method is compared with the standard tip deflection contacting technique and shows a significant improvement to reproducibility. The effect of excessive compressive strain at the contact was investigated, with a change from rectifying to ohmic I-V behaviour observed as compressive strain at the contact is increased, leading to irreversible changes to the electrical properties of the NW. The potential effect of current annealing the nanowire and contacts was considered and shown not to be a major contributing factor to the change in I-V behaviour. This work provides an ideal method for forming reproducible non-lithographic nanocontacts to a multitude of nanomaterials. This is the accepted version of the following article: Semiconductor Science and Technology , 30, 065011 (2015) doi:10.1088/0268-1242/30/6/065011 which has been published in final form at http://iopscience.iop.org/article/10.1088/02681242/30/6/065011/meta;jsessionid=39FECBC6EB9D553C63A6AF2DAE8C4BB 1.c1 for which the copyright is held by the Institute of Physics

If the silicon industry is to successfully integrate ZnO nanowires (NWs) into existing devices to fully utilise the piezoelectric or optical properties of ZnO NWs, then a detailed understanding of the effect of metal interconnects on the morphology of the NWs during growth needs to be obtained. In this study, ZnO NWs were hydrothermally grown at 90 °C on Au, Ni and a Si substrate control to mimic the typical surfaces of a MetalMUMPs MEMS chip. The growth rate was significantly affected by the metal film below the ZnO seed layer, which was mainly attributed to changes in the roughness and grain size of the seed layer deposited, with the growth rate decreasing with increasing roughness. The growth rate on Si and Au surfaces also increased when isolated from the Ni samples, suggesting that Ni cations released in the solution could also inhibit growth by electrostatically attaching to the NWs surface and acting as a barrier to the incorporation of zinc ions. Furthermore, photoluminescence studies show the addition of metal layers to the substrate reduces the optical quality of the produced ZnO NWs.