Dynamic redistribution of the electric field of the channel in AlGaN/GaN high electron mobility transistor with nanometer-scale gate length

Transport peculiarities and the physical origin of noise properties in AlGaN/GaN-based high electron mobility transistors (HEMTs) with a large ratio of channel length to gate length were investigated. Dependence of deviations of low-frequency noise spectra from the 1/f law on applied gate voltages was studied in an extended range of frequencies. The behavior is explained in terms of a model based on the dynamic redistribution of the electric field along the two-dimensional channel of the HEMT. The results show that the main contribution to the noise originates from the region under the gate and adjacent to the gate channel regions. (C) 2005 American Institute of Physics

Carrier relaxation in GaAs v-groove quantum wires and the effects of localization

Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove quantum wires (QWRs) with a large subband separation (46 meV). Signatures of inhibited carrier relaxation mechanisms are seen in temperature-dependent photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we observe strong emission from the first excited state of the QWR below ~50 K. This is attributed to reduced inter-subband relaxation via phonon scattering between localized states. Theoretical calculations and experimental results indicate that the pinch-off regions, which provide additional two-dimensional confinement for the QWR structure, have a blocking effect on relaxation mechanisms for certain structures within the v-groove. Time-resolved PL measurements show that efficient carrier relaxation from excited QWR states into the ground state, occurs only at temperatures > 30 K. Values for the low temperature radiative lifetimes of the ground- and first excited-state excitons have been obtained (340 ps and 160 ps respectively), and their corresponding localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct corrupt figure

The State of Strain in Single GaN Nanocolumns As Derived from Micro-Photoluminescence Measurements

In the present paper, studies on the state of strain in single and ensembles of nanocolumns investigated by photoluminescence spectroscopy will be presented. The GaN nanocolumns were either grown in a bottom-up approach or prepared in a top-down approach by etching compact GaN layers grown on Si(111) and sapphire (0001) substrates. Experimental evidence for strain relaxation of the nanocolumns was found. The difference and development of the strain value for different nanocolumns could be verified by spatially resolved micro-photoluminescence on single nanocolumns separated from their substrate. A common D0X spectral position at 3.473 eV was found for all separated single GaN nanocolumns independent of the substrate or processing technique used, as expected for a relaxed system

Resonant electron transfer between quantum dots

An interaction of electromagnetic field with a nanostructure composed of two quantum dots is studied theoretically. An effect of a resonant electron transfer between the localized low-lying states of quantum dots is predicted. A necessary condition for such an effect is the existence of an excited bound state whose energy lies close to the top of the barrier separating the quantum dots. This effect may be used to realize the reversible quantum logic gate NOT if the superposition of electron states in different quantum dots is viewed as the superposition of bits 0 and 1.Comment: 8 pages, 1 EPS-figure, submitted to Phys. Rev.

Net Charge on a Noble Gas Atom Adsorbed on a Metallic Surface

Adsorbed noble gas atoms donate (on the average) a fraction of an electronic charge to the substrate metal. The effect has been experimentally observed as an adsorptive change in the electronic work function. The connection between the effective net atomic charge and the binding energy of the atom to the metal is theoretically explored.Comment: ReVvTeX 3.1 format, Two Figures, Three Table

Consumers' Willingness to Pay for Quality and Safety in Clams

The aim of the research is to estimate the potential demand for certified clams in Italy and to investigate the determinants of maximum amount that respondents are willing to pay for this product. Quantitative analysis was used based on 1,067 face-to-face interviews collected in 3 Italian regions in the north bordering the Adriatic Sea (Friuli-Venezia Giulia, Veneto, and Emilia-Romagna) carried out during 2008. The consumers' willingness to pay (WTP) is measured using a contingent valuation method. In order to estimate separately the determinants of the probability that respondents are willing to pay and the maximum that they are willing to pay, a generalization of Tobit model was adopted. The results indicate that consumers are willing to pay a premium price mainly to purchase better quality products. The research provides some initial insight into consumers' WTP that can be useful for certified fish farming. © 2014 Taylor & Francis Group, LLC

Electrodeposition of Bi thin films on n-GaAs(111)B. I. Correlation between the overpotential and the nucleation process

Bismuth thin films constitute a promising nanostructure for the fabrication of spin-based devices. To achieve this goal, it is necessary to obtain high-quality Bi layers with controlled and reproducible properties. Therefore, studies focused on the understanding of the nucleation process and the correlation between the growth conditions and the film properties are of great interest. In this work, we have studied the electrodeposition of Bi thin films onto GaAs(111)B substrates at different overpotentials. In Part I, we have analyzed the nucleation of the films by means of potentiostatic curves. The current density transients have been deconvoluted into individual processes taking into account the energy band diagram of the semiconductor electrolyte interface. The deconvolution of the current density transients indicates that Bi electrodeposition follows a 3D nucleation controlled by diffusion, accompanied by concurrent processes such as both proton adsorption and reduction. The competition of these processes is controlled by the energy distribution of the surface states at the semiconductor electrolyte interface and determines the nucleation process. The correlation between the properties of the Bi films and the Bi/GaAs interface with the nucleation process, i.e., with overpotential, is discussed in detail in Part II of this work

Dispersive resonance bands within the space charge layer of metal- semiconductor junction

Based on measurements of angle resolved photoemission, we report that in the Pb/Ge(111)- \sqrt{3}x\sqrt{3} R30^\circ structure, in addition to three bands resembling Ge heavy hole (HH), light hole (LH), and split off (SO) bulk band edges, a fourth dispersive band resembling the non split off (NSO) band is found near the surface zone center. While three Ge bulk-like bands get distorted due to strong coupling between Pb and Ge, the NSO-like band gets weaker and disappears for larger thickness of Pb, which, when combined with ab initio calculations, indicates its localized nature within space charge layer. Our results are clearly important for designing electronics involved with metal-semiconductor contacts.Comment: 21 pages, 4 figures, Phys. Rev. B 81, 245406 (2010

Biosensoren auf der Basis des Insektengeruchssinns als Routine-Instrument - Eine Machbarkeitsstudie

Die Leistungsfähigkeit des kürzlich entwickelten BioFET auf der Basis des Insektengeruchssinns hängt sowohl von den Eigenschaften der Insektenantenne und denen des Feldeffekttransistors als auch von der Güte der bioelektronischen Schnittstelle zwischen Insektenantenne und Feldeffekttransistor ab. Die von Seiten der Insektenantenne notwendigen Voraussetzungen sollen durch einen Vergleich der Tauglichkeit von Insektenantennen zweier verschiedener Insektenarten, dem Kartoffelkäfer (Leptinotarsa decemlineata) und dem Stahlblauen Kiefernprachtkäfer (Phaenops cyanea) für die Messung von Pflanzenschäden in unterschiedlichen Umgebungen veranschaulicht werden. Dabei steht der Abgleich der Eigenschaften der Biokomponenten hinsichtlich ihrer sensorischen Leistungsfähigkeit durch die Anwendung im Vordergrund. Für die praktische Anwendung des Biosensor-Systems im Routineeinsatz sind oftmals noch andere Eigenschaften, wie Verfügbarkeit des Sensorköpfe, zeitliche und räumliche Auflösung der Messungen sowie der Bedarf an Energie und ausgebildeten Arbeitskräften maßgeblich. Diese Parameter können durch Anzuchtbedingungen der Insekten, Lagerbarkeit der Bio- und der Halbleiterkomponente sowie technische Optionen des Biosensor-Systems beeinflusst werden. Die Fertigung eines Biosensors auf der Basis des Insektengeruchssinns nach Kundenwunsch erfordert eine sorgfältige Beschreibung der Sensor-Anwendung, die durch eine gründliche Kenntnis des biologischen Hintergrunds der verwendeten Insekten und der technischen Limitierungen bzw. Optionen von Transducer-Komponente und Biosensor-System ergänzt werden muss. Die Möglichkeit halbautomatischer Fertigungstechniken zur Herstellung der Sensorköpfe werden diskutiert und zukünftiges Entwicklungspotential aufgezeigt. Auf dieser Basis ist die Entwicklung von routinemäßig einsetzbaren Biosensoren auf der Basis des Insektengeruchssinns für die vor-Ort-Analytik von Duftstoffen in vielfältigen Anwendungen möglich