Ferdinand Gasparyan

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.

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...

Theory of 1f noise in medium and far infrared photodetectors

Abstract The present report is denoted to the theory of infrared photodiode low frequency noise based on homogeneous and nondegenerate semiconductors. The results of the theoretical calculation are extended to include photodiodes made of elementary semiconductors, as well as of chalcogenides and solid solutions band structures which are described through a two-band Kane model. The kinetic equations of Boltzmann for the system of electrons and phonons are used to calculate the spectral density noise. In the calculation, only the electron-phonon interactions have been taken into consideration. For low frequency noise spectrum an expression is obtained which is well matched with the experimental formula Hooge.

Single trap in liquid gated nanowire FETs: Capture time behavior as a function of current

The basic reason for enhanced electron capture time, τc, of the oxide single trap dependence on drain current in the linear operation regime of p+-p-p+ silicon field effect transistors (FETs) was established, using a quantum-mechanical approach. A strong increase of τc slope dependence on channel current is explained using quantization and tunneling concepts in terms of strong field dependence of the oxide layer single trap effective cross-section, which can be described by an amplification factor. Physical interpretation of this parameter deals with the amplification of the electron cross-section determined by both decreasing the critical field influence as a result of the minority carrier depletion and the potential barrier growth for electron capture. For the NW channel of n+-p-n+ FETs, the experimentally observed slope of τc equals (−1). On the contrary, for the case of p+-p-p+ Si FETs in the accumulation regime, the experimentally observed slope of τc equals (−2.8). It can be achieved when the amplif...

Low-Frequency Noise Spectroscopy at Nanoscale: Carbon Nanotube Materials and Devices

This section presents brief description of peculiarities of carbon materials and advantages of noise spectsroscopy for the study of unique carbon nanotubes (CNT) materials and devices. In general, carbon is truly an extraordinary material with physical structures spanning three dimensional (3D) graphite, two-dimensional (2D) graphene and zero-dimensional (0D) buckyballs or buckminster fullerine spheres. It is not surprising that the structural characteristics of carbon thus yield band diagrams displaying a diverse array of physical properties. When a 2D graphene sheet is rolled into a cylinder, a one-dimensional (1D) or quasi-1D form of carbon results, namely CNTs, which have been one of the most extensively studied materials since their discovery. A single rolled-up sheet of graphene results in a single-walled nanotube (SWNT) with a typical diameter of 1 – 2 nm. The rolling direction is characterized by a chiral index ( , ) n m . Achiral zigzag ( ,0) n and armchair ( , ) n n CNTs are distinguished from the rest (chiral CNTs). Armchair tubes are always metallic, while zigzag tubes can be semiconducting or metallic (Reich et al., 2004). Multi-walled nanotubes (MWNTs) consist of concentric cylinders with an interlayer spacing of 0.3 – 0.4 nm, and diameters that are at least an order of magnitude larger than SWNTs, between 10 – 30 nm. CNTs have high elastic modulus, strength, show efficient conductivity of heat, exhibit high thermal and chemical stability, flexibility, low mass density, and unique electrical properties (metallic conductivity and semiconductivity) which makes them excellent candidates for nano-devices and polymer composite materials (Sanchez-Pomales et al., 2010; Service, 1998). At the same time the CNTs are extremely difficult to manage due to their low solubility in both aqueous and organic solvents, which restrict the extent of their applications. Therefore one of the main challenges is the need for the development of new functionalization chemistries that can increase the solubility of CNTs without altering their CNTs properties. Transport in the CNTs of molecular SWand MWNT-field-effect transistors (FETs) is dominated by holes and, at room temperature, it appears to be diffusive (Martel et al., 1998). Using the gate electrode, the conductance of a SWNT-FET is modulated

Temperature Chaos and the Lattice Character of the Hooge Parameter in Semiconductors

The influence of the electron–phonon interaction on formation of the low-frequency noise in semiconductors is theoretically considered. The determining role of scattering mechanisms in formation of the 1/f low frequency noise is shown. The temperature dependence of the Hooge parameter αH is revealed and explained. The lattice character of αH is proven.

MODIFIED CHARGE FLUCTUATION NOISE MODEL FOR ELECTROLYTE-INSULATOR-SEMICONDUCTOR DEVICES

A modified charge fluctuation low-frequency noise model for an electrolyte-insulator-semiconductor (EIS) structure is developed. Physical processes in the semiconductor, insulator and electrolyte medium responsible for low-frequency charge fluctuation are discussed based on an electrical equivalent scheme for the EIS structure. Noise spectral density dependence on charge concentration fluctuation related to processes on the electrolyte-insulator, insulator-semiconductor interfaces and bulk semiconductor are analyzed.

1/f ‐ type Noise in View of Phonons Interface Percolation Dynamics

The influence of long‐wave acoustic longitudinal‐phonon percolation dynamics on 1/f ‐type noise level is modeled for homogeneous, non‐degenerated and bounded semiconductors. Phonons percolation from semiconductor media to environment regions via so‐called «refraction points» of phonons’ wave vector phase space is modeled within framework of the bulk mechanism of electron lattice mobility fluctuation. On the base of this mechanism it is shown, that semiconductor surface is the source of suppression of 1/f‐noise. It is indicated that in some certain applications of the Fluctuation Theory it is physically correct to use Schonfeld model to consider 1/f noises in semiconductors.

Current carrier mobility fluctuations in homogeneous semiconductors

The two main causes of origin of the mobility fluctuation of the electrons in homogeneous, unlimited, and non-degenerated semiconductors are discussed. It is shown that the mobility fluctuation is conditioned by the symmetric component of the fluctuation of the distribution function, i.e. by the fluctuations of the conduction electrons energy. On the base of the developed quasi-classical model the spectrum of electrons lattice mobility fluctuations is calculated. In the frequency wide variation range it has 1/f form.

An IR-Radiometer with Internal Signal Modulation

An infrared (IR) radiometer electrical circuit on the basis of photoresistors and photodiodes made of silicon doped with zinc (Si) as well as the narrow bandgap semiconductor alloy Pb0.78Sn0.22Te is presented. In the circuit suggested a bridge with the photoreceiver connected to the radiometer input and immediately fed by signal generators functions as a radiation modulator. The threshold sensitivity turned out on a recorder is 2·10−13 W·Hz−1/2 (for the n+−n−n+ structures made of Si, λ=0.8−l.2μm, T=300K); 1.4·10−15W·Hz−1/2 (for p+−n−n+ S-diodes on the basis of Si, λ=0.8−1.2μm, T=300K) and 10−12W·Hz1/2 (for photodiodes on the basis of Pb0.78Sn0.22Te, λ=8−13μm, T=77K).