M. V. Petrychuk

Separation of hot-electron and self-heating effects in two-dimensional AlGaN/GaN-based conducting channels

We address experimental and theoretical study of a two-dimensional electron gas transport at low and moderate electric fields. The devices under study are group-III nitride-based (AlGaN/GaN) gateless heterostructures grown on sapphire. The transmission line model patterns of different channel lengths, L, and of the same channel width are used. A strong dependence of the device I–V characteristics on the channel length has been found. We have developed a simple theoretical model to adequately describe the observed peculiarities in the I–V characteristics measured in steady-state and pulsed (10−6 s) regimes. The effect of the Joule heating of a heterostructure is clearly distinguished. The thermal impedance and the channel temperature rise caused by the Joule self-heating have been extracted for the devices of different L at different values of dissipated power. The current reduction due to both self-heating and hot-electron effects is determined quantitatively as a function of the electric field.

Transport properties of single-walled carbon nanotube transistors after gamma radiation treatment

Single-walled carbon nanotube field-effect transistors (CNT-FETs) were characterized before and after gamma radiation treatment using noise spectroscopy. The results obtained demonstrate that in long channel CNT-FETs with a length of 10 μm the contribution of contact regions can be neglected. Moreover, radiation treatment with doses of 1×106 and 2×106 rad allows a considerable decrease parallel to the nanotube parasitic conductivity and even the shift region with maximal conductivity to the voltage range of nearly zero gate voltage that improves the working point of the FETs. The Hooge parameters obtained before and after gamma radiation treatment with a dose of 1×106 rad are found to be about 5×10−3. The parameters are comparable with typical values for conventional semiconductors.

Liquid and Back Gate Coupling Effect: Toward Biosensing with Lowest Detection Limit

We employ noise spectroscopy and transconductance measurements to establish the optimal regimes of operation for our fabricated silicon nanowire field-effect transistors (Si NW FETs) sensors. A strong coupling between the liquid gate and back gate (the substrate) has been revealed and used for optimization of signal-to-noise ratio in subthreshold as well as above-threshold regimes. Increasing the sensitivity of Si NW FET sensors above the detection limit has been predicted and proven by direct experimental measurements.

Mechanisms of current formation in resonant tunneling AlN∕GaN heterostructures

This paper presents an analysis of transport and noise properties of double-barrier resonant tunneling diodes formed on the basis of AlN∕GaN heterostructures. Two stable states are registered in the I-V characteristics of the diodes. The temperature dependences of current and noise behavior are analyzed to understand the contribution of different mechanisms responsible for current formation in the structures. The evolution of the spectral density of the noise current with temperature reveals several recombination-generation components. The mechanisms responsible for the formation of current in AlN∕GaN∕AlN diodes are discussed taking into account the Poole-Frenkel effect.

Excess low-frequency noise in AlGaN'GaN-based high-electron-mobility transistors

The low-frequency 1/f noise characteristics of AlGaN/GaN high-electron-mobility transistors with gate length scaled down to 150 nm grown on sapphire by metalorganic chemical vapor deposition have been studied. Certain features of the 1/f noise have been revealed in these short-gate transistors. The low-frequency noise spectra show drastically different behavior depending on the gate voltage VG in the range of low (VGt⩽VG⩽0) and high (VG<VGt) biases. The noise spectra-gate bias dependences allow one to distinguish a spatial redistribution of effective noise sources in the transistor channel. The Hooge parameter has been deduced separately for the ungated region, αHp≃10−3, and for the gated region, αHa≃2×10−4, of the transistor channel. These values are as low as those previously observed in nitride heterostructures grown on silicon carbide substrates.

Low-Frequency Noise in Field-Effect Devices Functionalized With Dendrimer/Carbon- Nanotube Multilayers

Low-frequency noise in an electrolyte-insulator-semiconductor (EIS) structure functionalized with multilayers of polyamidoamine (PAMAM) dendrimer and single-walled carbon nanotubes (SWNT) is studied. The noise spectral density exhibits dependence with the power factor of and for the bare and functionalized EIS sensor, respectively. The gate-voltage noise spectral density is practically independent of the pH value of the solution and increases with increasing gate voltage or gate-leakage current. It has been revealed that functionalization of an EIS structure with a PAMAM/SWNTs multilayer leads to an essential reduction of the noise. To interpret the noise behavior in bare and functionalized EIS devices, a gate-current noise model for capacitive EIS structures based on an equivalent flatband-voltage fluctuation concept has been developed.

Modulation phenomena in Si nanowire field-effect transistors characterized using noise spectroscopy and gamma radiation technique

High-quality silicon nanowire (NW) field-effect transistors (FETs) were designed and fabricated. Features of transport and modulation phenomena of the structures were studied using a number of techniques, including noise spectroscopy. Using the 1/f noise component level, the values of the volume trap densities in gate dielectric are estimated to be around 1 × 1017 cm−3 eV−1. This result proves high quality of the investigated structures. Analysis of Lorentzian noise components of NW samples is used to characterize single trap and its parameters. A strong modulation of carrier concentration in the conducting channel under influence of even single carrier capture event has been revealed. Possibility of fine tuning of the transport properties of the sample with low-dose gamma irradiation has been shown. The gamma radiation treatment of the NW samples was applied as an effective technique to confirm the strong influence of trap charges on conductivity behavior in the channel of NW FETs. The results demonstrat...

Molecular dynamics study of the primary ferrofluid aggregate formation

Abstract Investigations of the phase transitions and self-organization in the magnetic aggregates are of the fundamental and applied interest. The long-range ordering structures described in the Tomaneks systematization (M. Yoon, and D. Tomanek, 2010 [1] ) are not yet obtained in the direct molecular dynamics simulations. The resulted structures usually are the linear chains or circles, or, else, amorphous (liquid) formations. In the present work, it was shown, that the thermodynamically equilibrium primary ferrofluid aggregate has either the long-range ordered or liquid phase. Due to the unknown steric layer force and other model idealizations, the clear experimental verification of the real equilibrium phase is still required. The predicted long-range ordered (crystallized) phase produces the faceting shape of the primary ferrofluid aggregate, which can be recognized experimentally. The medical (antiviral) application of the crystallized aggregates has been suggested. Dynamic formation of all observed ferrofluid nanostructures conforms to the Tomaneks systematization.

Single trap dynamics in electrolyte-gated Si-nanowire field effect transistors

Liquid-gated silicon nanowire (NW) field effect transistors (FETs) are fabricated and their transport and dynamic properties are investigated experimentally and theoretically. Random telegraph signal (RTS) fluctuations were registered in the nanolength channel FETs and used for the experimental and theoretical analysis of transport properties. The drain current and the carrier interaction processes with a single trap are analyzed using a quantum-mechanical evaluation of carrier distribution in the channel and also a classical evaluation. Both approaches are applied to treat the experimental data and to define an appropriate solution for describing the drain current behavior influenced by single trap resulting in RTS fluctuations in the Si NW FETs. It is shown that quantization and tunneling effects explain the behavior of the electron capture time on the single trap. Based on the experimental data, parameters of the single trap were determined. The trap is located at a distance of about 2 nm from the inte...

Power and temperature dependence of low frequency noise in AlGaN∕GaN transmission line model structures

The low-frequency noise in AlGaN∕GaN transmission line model structures has been investigated for a wide range of ambient temperatures and dissipated powers. A deviation of low-frequency noise from a 1∕f dependence has been observed upon increasing the applied voltage. The effect correlates with the nonlinearity of current-voltage characteristics (CVC). The concept of nonequilibrium 1∕f noise has been introduced to explain 1∕f noise enhancement. A qualitative model connecting non-equilibrium noise with nonlinearity of the CVC via a common origin—nonuniform overheating of the structures—has been suggested. Furthermore, deviations of equilibrium noise from the 1∕f law at low temperatures have been observed and studied.