Unipolar and bipolar operation of InAs/InSb nanowire heterostructure field-effect transistors

We present temperature dependent electrical measurements on n-type InAs/InSb nanowireheterostructurefield-effect transistors. The barrier height of the heterostructure junction is determined to be 220 meV, indicating a broken bandgap alignment. A clear asymmetry is observed when applying a bias to either the InAs or the InSb side of the junction. Impact ionization and band-to-band tunneling is more pronounced when the large voltage drop occurs in the narrow bandgapInSb segment. For small negative gate-voltages, the InSb segment can be tuned toward p-type conduction, which induces a strong band-to-band tunneling across the heterostructucture junction.This work was carried out within the Nanometer Structure Consortium at Lund University and was supported by the Swedish Research Council (VR), the Swedish Foundation for Strategic Research (SSF), and the Knut and Alice Wallenberg Foundation

Thin electron beam defined hydrogen silsesquioxane spacers for vertical nanowire transistors

A method to fabricate inorganic vertical spacer layers with well-controlled thickness down to 40 nm using electron beam exposure is demonstrated. These spacers are suitable in vertical nanowire transistor configuration. As spacer material, the authors use hydrogen silsesquioxane (HSQ), a material with low permittivity and high durability. They show that the resulting HSQ thickness can be controlled by electron dose used and it also depend on the initial thickness of the HSQ layer. To achieve good reproducibility, the authors found it necessary to fully submerge the nanowires beneath the HSQ layer initially and that the thickness of HSQ before exposure needs to be determined. Finally, they introduce these steps in an existing transistor process and demonstrate vertical nanowire transistors with high performance. (C) 2014 American Vacuum Society

Heterogeneous integration of InAs on W/GaAs by MOVPE

InAs has been grown on W-GaAs patterned substrates using MOVPE. The selectivity of the growth and the nucleation process has been studied as a function of the temperature and the V/III-ratio in the MOVPE reactor. It is shown that the W guides the nucleation of the InAs on the GaAs and that the islands formed may be used to embed metal features in a hybride InAs/GaAs structure in agreement with previous overgrowth studies of W-InAs and W-GaAs. The electrical properties has also been evaluated demonstrating a reduction of resistance by a factor 5 for a hybride structure with an embedded grating as compared to an InAs/GaAs reference sample

Vertical nanowire TFETs with channel diameter down to 10 nm and point S MIN of 35 mV/decade

We present experimental data from vertical InAs/InGaAsSb/GaSb nanowire tunnel field-effect transistors with channel diameter scaled down to 10 nm and ability to reach a point subthreshold swing of 35 mV/decade at VDS = 0.05 V. Furthermore, the impact of drain, channel and source diameter scaling on the subthreshold swing and currents are studied. Impact of gate-overlap is more evident for devices with highly scaled source due to strong reduction of the current. Furthermore, small channel diameter makes these devices more susceptible to Random Telegraph Signal noise

Qualitative comparison of several phase correction algorithms in single-image in-line X-ray phase contrast tomography

In recent years, phase contrast has gained importance in the field of X-ray imaging and more particular in high-resolution X-ray computed tomography or micro-CT. For phase propagation imaging, no additional hardware or specific setup is required, which makes the effect inherent to micro-CT where it is manifested as an edge-enhancement effect. As such, it can be beneficial for qualitative analysis of a 3D volume. Nevertheless, it induces unreal gray values and is thus often considered as an imaging artefact which hinders proper quantitative 3D analysis. Several methods exist to reduce this phase contrast effect or to retrieve the phase information from the mixed phase-and-amplitude images. In this presentation, a comparison will be made between 2 phase retrieval algorithms and 2 phase correction algorithms. Of these 2 latter, one can be performed on the reconstructed volume, which clearly facilitates the operation of phase correction

Electrical characterization of thin InAs films grown on patterned W/GaAs substrates

InAs has been grown on W-GaAs patterned substrates using metal organic vapor phase epitaxy. It is shown that the W pattern guides the nucleation of the InAs on the GaAs substrate and that the islands formed may be used to embed metal features in a hybrid InAs/GaAs structure. A lower resistance (factor of 2) was measured for the hybrid structures as compared to reference structures. The reduction in the resistance is attributed to an increased carrier concentration as observed from Hall measurements on devices with different tungsten densities. Cross-sectional transmission electron microscopy investigations reveal a void-free overgrowth above the metal despite the large mismatch of the InAs/GaAs system. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3222859

1/f-noise in Vertical InAs Nanowire Transistors

The material quality at high-k interfaces are a major concern for FET devices. We study the effect on two types of InAs nanowire (NW) transistors and compare their characteristics. It is found that by introducing an inner layer of Al2O3 at the high-kappa interface, the low frequency noise (LFN) performance regarding gate voltage noise spectral density, S-Vg, is improved by one order of magnitude per unit gate area

Scaling of Vertical InAs–GaSb Nanowire Tunneling Field-Effect Transistors on Si

We demonstrate improved performance due to enhanced electrostatic control achieved by diameter scaling and gate placement in vertical InAs-GaSb tunneling field-effect transistors integrated on Si substrates. The best subthreshold swing, 68 mV/decade at VDS=0.3 V, was achieved for a device with 20-nm InAs diamter. The on-current for the same device was 35 µA/µm at VGS=0.5 V and VDS=0.5 V. The fabrication technique used allows downscaling of the InAs diameter down to 11 nm with a flexible gate placement

Increased absorption in InAsSb nanowire clusters through coupled optical modes

Nanowires can act as efficient light absorbers where waveguide modes are resonant to specific wavelengths. This resonant wavelength can easily be tuned by the nanowire dimensions, but the absorption of infrared radiation requires diameters of hundreds of nm, which is difficult to achieve using epitaxial growth. Here, we demonstrate that infrared absorption in InAsSb nanowires with the diameters of only 140 nm grown on Si substrates can be enhanced resonantly by placing them closely packed in clusters of different sizes. We find that coating the nanowires with a dielectric to optically connect them results in an efficient absorption diameter far exceeding the diameter of the constituent nanowires and that the cut-off wavelength is redshifted with an increasing cluster diameter. Numerical simulations are in agreement with the experimental results and demonstrate that if nanowires are positioned in clusters, a peak absorptance of 20% is possible at 5.6 μm with only 3% surface coverage. This absorptance is 200 times higher than for wires placed in an equidistant pattern. Our findings have direct implications for the design of efficient nanowire based photodetectors and solar cells