Extrinsic Region Research Articles

Semiconducting properties of Cu2In3VO9 ceramic material

Cu2In3VO9 has been characterized by UV–vis–NIR and dielectric spectroscopy and measurements of its electrical conductivity and thermoelectric power to be a semiconductor with the activation energy Ea1=0.61eV and Ea2=0.03eV in the intrinsic and extrinsic region, respectively, the direct allowed energy gap Eg =1.09eV, the change of sign of the thermoelectric power from p to n at Tn-p=400K, the strongly temperature-dependent and frequency both dielectric constant (εr) and loss tangent (tanδ) above 160K. Moreover, the I-V characteristics and conductance provided the evidence of symmetrical and non-linear behaviour typical of strong emission of charge carriers induced by temperature and voltage. These results are interpreted in the framework of vacancy acceptor and donor levels in the honeycomb lattice structure forming a two-dimensional frustrated system assuming the relaxation process like with Maxwell-Wagner or Jonscher.

Light-Controlled ZrO2 Surface Hydrophilicity.

In recent years many works are aimed at finding a method of controllable switching between hydrophilicity and hydrophobicity of a surface. The hydrophilic surface state is generally determined by its energy. Change in the surface energy can be realized in several different ways. Here we report the ability to control the surface wettability of zirconium dioxide nano-coatings by changing the composition of actinic light. Such unique photoinduced hydrophilic behavior of ZrO2 surface is ascribed to the formation of different active surface states under photoexcitation in intrinsic and extrinsic ZrO2 absorption regions. The sequential effect of different actinic lights on the surface hydrophilicity of zirconia is found to be repeatable and reversibly switchable from a highly hydrophilic state to a more hydrophobic state. The observed light-controllable reversible and reproducible switching of hydrophilicity opens new possible ways for the application of ZrO2 based materials.

Impact of Lateral Scaling on Silicon Germanium High Breakdown Power Amplifier Device Performance

Silicon Germanium (SiGe) Heterojunction Bipolar Transistors (HBTs) in Bipolar Complementary Metal Oxide Semiconductor (BiCMOS) technologies have in recent years, emerged as a viable alternative to Gallium Arsenide (GaAs) [1] for commercial development of linear power amplifier (PA) modules for wireless communications. The explosion in WLAN applications at 2.4GHz has provided ample opportunity for SiGe BiCMOS to substantially penetrate the PA market [2]. SiGe HBTs offer several benefits compared to it’s GaAs HBT counterparts including the ability to provide high integration at a reduced cost [3]. The higher thermal conductivity associated with the silicon substrate enables reduced chip areas, smaller packages and provides improvements in chip robustness. Additionally, SiGe BiCMOS integration facilitates improved power densities, on-chip matching and bias chokes, temperature compensated power detector and a CMOS compatible interface [2]. SiGe HBT PA device design limits have traditionally been constrained by the performance tradeoff described by the Johnson limit, which states that the product of the current gain, fT and the DC open-base breakdown voltage, BVceo, should be relatively constant[3]. However, it is now generally accepted that DC emitter-open breakdown voltage, BVcbo is a more useful indicator of device ruggedness for PA applications. This arises since SiGe HBT operation in PA applications have been demonstrated at voltages significantly higher than BVceo, [1,4]. Furthermore, power-gain cut-off frequency, fMAX , has also been cited as relevant a device metric for PAs as fT , [1,3] and several authors have suggested that improvements in fMAX will enhance PA device performance. Typically, improvements in device fMAX are achieved by lateral scaling to accomplish a reduction in the base resistance and collector-base capacitance. Since SiGe HBT device physics do not demand rigid tradeoff between BVcbo and fMAX, , several potential device optimization opportunities exist for PA applications. Technology computer-aided design (TCAD) has been used to optimize the PA design performance relative to the base technology. The TCAD methodology was based on a detailed strategy which entailed developing a process and device model calibration for an existing 0.35um SiGe HBT device that features non-self-aligned emitter-base integration, with a carbon doped SiGe base layer and an implanted extrinsic base region [2]. The model calibration featured a close match of both process and electrical characteristics to the measured data. An important element to matching the electrical characteristics of the device, was simulating key artifacts of the process related to epitaxial growth of the SiGe base layer, which defined the final device topology. The calibration served as the baseline simulation for the optimization study and provided insight into the device performance limitations. The simulations demonstrated the device breakdown, BVcbo, occurs along the extrinsic region of the collector and the base, and is correspondingly set by the thickness of the collector n-epitaxial layer and the vertical diffusion of the extrinsic base into the collector. Several lateral scaling strategies were therefore investigated, which addressed optimization of collector-base capacitance, Ccb and base resistance, Rb for improvements in fMAX and BVcbo. Scaling the lateral dimension of the device resulted in improvements in the performance metrics peak fT , peak Ic and fMAX . Improvements in fT and Ic are explained by the reduced surface field effect, whereby a more uniform field distribution delays base push out effect in the transistor[5]. The AC and DC characteristcs will be reviewed.

Opto-electronic Properties of Mid-Wavelength: n Type II InAs/InAs1−x Sb x and Hg1−x Cd x Te

There is significant interest in mid-wavelength type II strained layer superlattices (SLSs) and HgCdTe material systems for background limited performance, operating at significantly higher temperature, T ≥ 150 K, than InSb, T ≈ 80–90 K. A precise knowledge of the electronic and optical properties of these materials is desirable since they determine detector performance and are needed for input parameters in self-consistent physics-based predictive models. Recently, data on the optical absorption coefficient, and the hole minority carrier lifetime has become available, suggesting that in the extrinsic region the limiting recombination processes in mid-wavelength type II Ga-free SLSs are radiative and Shockley–Read–Hall (SRH). These findings provide the opportunity for comparisons with mid-wavelength HgCdTe. The comparisons show that the radiative recombination coefficients are similar; however, the SRH lifetime limited to 9 μs for the SLS implies that the dark current density is expected to be limited by bulk generation–recombination (G–R) SRH processes for temperatures below 160 K; hence requiring heterojunction designs to suppress the G–R dark currents and be diffusion limited. Mid-wavelength infrared HgCdTe photodiodes are shallow p+n photovoltaic devices and because of the very long SRH hole lifetime are diffusion radiatively limited photodiodes down to 80 K.

Electrical properties of as-grown and proton-irradiated high purity silicon

The complex permittivity of as-grown and proton-irradiated samples of high purity silicon obtained by the floating zone method was measured as a function of temperature at a few frequencies in microwave spectrum by employing the quasi TE011 and whispering gallery modes excited in the samples under test. The resistivity of the samples was determined from the measured imaginary part of the permittivity. The resistivity was additionally measured at RF frequencies employing capacitive spectroscopy as well as in a standard direct current experiment. The sample of as-grown material had the resistivity of ∼85kΩcm at room temperature. The sample irradiated with 23-MeV protons had the resistivity of ∼500kΩcm at 295K and its behavior was typical of the intrinsic material at room and at elevated temperatures. For the irradiated sample, the extrinsic conductivity region is missing and at temperatures below 250K hopping conductivity occurs. Thermal cycle hysteresis of the resistivity for the sample of as-grown material is observed. After heating and subsequent cooling of the sample, its resistivity decreases and then slowly (∼50h) returns to the initial value.

ELECTRICAL CONDUCTIVITY OF THE KAOLIN CLAY MINERAL DEPENDING ON THE TEMPERATURE

The aim is to study temperature dependence of the electrical conductivity of the kaolin mineral on crystalchemical factors and thermal transformations. Methods. We have applied the method of investigation of geo-electric properties of high-resistivity materials. Results. We gained the results of the study of the temperature dependence of electrical conductivity in the range of 100-1000 °C of the kaolin clay mineral, which is of great scientific and practical importance. We have proved the existence of the general laws of the nature of the change in the electrical conductivity within the temperature range for all the samples studied, due to the existence of associated complexes of elementary defects in the crystal lattice of the mineral, which play an essential role in the kinetic nature in the geosphere of the Earth. Availability of the spectrum values of the activation energy in the extrinsic region characterizes the stepped nature of dehydroxylation and delocalization of protons of hydroxyl groups of non-equivalent positions of power in the crystal lattice of the mineral, which characterizes the formation of fluid regime of sedimentary strata in dehydration. Conclusions. It was found that the behavior of the electrical conductivity is interconnected with the processes caused by the existence of elementary defects associated in complexes in the crystal lattice of the mineral. The range of values of the activation energy of conductivity reflects the process of dehydroxylation and delocalization of protons and hydroxyl groups.

Visual motion imagery neurofeedback based on the hMT+/V5 complex: evidence for a feedback-specific neural circuit involving neocortical and cerebellar regions

Objective. Current approaches in neurofeedback/brain–computer interface research often focus on identifying, on a subject-by-subject basis, the neural regions that are best suited for self-driven modulation. It is known that the hMT+/V5 complex, an early visual cortical region, is recruited during explicit and implicit motion imagery, in addition to real motion perception. This study tests the feasibility of training healthy volunteers to regulate the level of activation in their hMT+/V5 complex using real-time fMRI neurofeedback and visual motion imagery strategies. Approach. We functionally localized the hMT+/V5 complex to further use as a target region for neurofeedback. An uniform strategy based on motion imagery was used to guide subjects to neuromodulate hMT+/V5. Main results. We found that 15/20 participants achieved successful neurofeedback. This modulation led to the recruitment of a specific network as further assessed by psychophysiological interaction analysis. This specific circuit, including hMT+/V5, putative V6 and medial cerebellum was activated for successful neurofeedback runs. The putamen and anterior insula were recruited for both successful and non-successful runs. Significance. Our findings indicate that hMT+/V5 is a region that can be modulated by focused imagery and that a specific cortico-cerebellar circuit is recruited during visual motion imagery leading to successful neurofeedback. These findings contribute to the debate on the relative potential of extrinsic (sensory) versus intrinsic (default-mode) brain regions in the clinical application of neurofeedback paradigms. This novel circuit might be a good target for future neurofeedback approaches that aim, for example, the training of focused attention in disorders such as ADHD.

An Improved Virtual-Source-Based Transport Model for Quasi-Ballistic Transistors—Part I: Capturing Effects of Carrier Degeneracy, Drain-Bias Dependence of Gate Capacitance, and Nonlinear Channel-Access Resistance

In this paper, an improved physics-based virtual-source (VS) model to describe transport in quasi-ballistic transistors is discussed. The model is based on the Landauer scattering theory, and incorporates the effects of: 1) degeneracy on thermal velocity and mean free path of carriers in the channel; 2) drain-bias dependence of gate capacitance and VS charge, including the effects of band nonparabolicity; and 3) nonlinear resistance of the extrinsic device region on $g_{m}$ -degradation at high drain currents in the channel. The improved charge model captures the phenomenon of reduction in VS charge under nonequilibrium transport conditions in a quasi-ballistic transistor.

An Improved Virtual-Source-Based Transport Model for Quasi-Ballistic Transistors—Part II: Experimental Verification

In the first part of this two-part paper, a revised MIT virtual-source (MVS)-based transport model, called MVS-2, is presented. The MVS-2 model captures the essential physics of quasi-ballistic nanotransistors by accounting for the effects of: 1) degeneracy on the thermal velocity and the mean free path of the carriers in the channel; 2) nonequilibrium transport conditions on the gate–channel capacitance; and 3) the conduction band nonparabolicity on the effective mass of the carriers. The formulation of the extrinsic device regions as nonlinear current-dependent resistances allows MVS-2 to describe the degradation in the device transconductance under high drain currents as measured experimentally in InGaAs quantum well HEMT devices. In this paper, we test the accuracy of the MVS-2 model by comparing the model results with the measured $I$ – $V$ data of the InGaAs HEMT devices with gate lengths from 30 to 130 nm and Si extremely thin silicon on insulator devices with gate lengths from 30 to 50 nm. We also discuss why at the expense of some physical rigor the basic MVS model can fit more simply the experimental data (except for the degradation in transconductance under high drain currents).

Extrapolation of Transport Properties and Figure of Merit of a Thermoelectric Material

The accurate determination of the thermoelectric properties of a material becomes increasingly difficult as the temperature rises. However, it is the properties at elevated temperatures that are important if thermoelectric generator efficiency is to be improved. It is shown that the dimensionless figure of merit, ZT, might be expected to rise with temperature for a given material provided that minority carrier conduction can be avoided. It is, of course, also necessary that the material should remain stable over the whole operating range. We show that the prediction of high temperature properties in the extrinsic region is possible if the temperature dependence of carrier mobility and lattice thermal conductivity are known. Also, we show how the undesirable effects arising from mixed or intrinsic conduction can be calculated from the energy gap and the relative mobilities of the electrons and the positive holes. The processes involved are discussed in general terms and are illustrated for different systems. These comprise the bismuth telluride alloys, silicon-germanium alloys, magnesium-silicon-tin and higher manganese silicide.

Impedance Spectroscopy in Ni<sub>0.3</sub>Zn<sub>0.7</sub>Fe<sub>2</sub>O<sub>4</sub>

Abstract. Impedance spectroscopies were used to investigate the electrical properties of spinel Ni0.3Zn0.7Fe2O4 (NZF) ceramics. Measurement was done using NOVO Dielectric Spectrometer from frequency 0.01 Hz to 3 x 106 Hz at temperature 30°C to 200°C. Resistivity response phenomena had been observed in sample sintered at 1100°C and carriers involved are mainly due to electron hopping mechanism between n-type and p-type carriers. The high and low response of grain and grain boundary regions were determined by plotting imaginary part versus real part of resistivity. An equivalent RC circuit of the experimental result had been constructed using a model that had been proposed by Hill and Pickup (1985). The model consists of parallel combination of 2 Havriliak-Negami (1966) model, resistivity and dielectric constant where ρ = 5.79 x 106 Ωm and ε = 4.45. It is found that 0.40 ± 0.01 eV, 0.14 ± 0.01 eV and 0.13 ± 0.01 eV and 0.38 ± 0.01 eV (extrinsic region) and 0.50 ± 0.01 eV (intrinsic region) for ac and dc activation energy respectively by using Arrhenius plot.

Low temperature magneto-dielectric measurements on BiFeO3 lightly substituted by cobalt

Dielectric and magnetodielectric measurements are done on BiFe1−xCoxO3: x = 0, 0.01, and 0.02 in the temperature range 70–300 K and up to magnetic field 1.3 T. The dielectric data are well described by Haverliak–Negami expression plus an additional term for the Maxwell Wagner (MW) type relaxations, whose contribution is dominant near room temperature. The parameters obtained from the fitting of data using the above mentioned expression, suggest slowing down of relaxation and approach towards ideal Debye type relaxations, as the temperature is lowered. The dielectric relaxations obey polaronic variable range hopping model with distinct activation energies (Ea) in the extrinsic (6.67T3/4 meV) and intrinsic (2.88T3/4 meV) regions for the parent sample (x = 0), and thus a distinct transition from extrinsic to intrinsic behavior is seen at 215 K while lowering the temperature. This distinct transition is missing for Co substituted samples probably due to the extrinsic region values of Ea (3.42T3/4 meV and 2.42T3/4 meV for x = 0.01 and 0.02, respectively) comparable to that of the intrinsic region (see x = 0). The magnetodielectric measurement shows positive magnetodielectricity (MD) in the intrinsic region (T < 215 K for x = 0) and negative MD in the extrinsic region (T > 215 K for x = 0). The extrinsic region is found to be dominated by MW and magnetoresistance effects, whereas MD in intrinsic regions is due to the spin reorientation transitions. The Co substitution is found to increase the extrinsic and non-Debye contributions to dielectricity, which becomes so large that no spin reorientation transitions are seen in x = 0.02 sample. The pyroelectric active region in x = 0 is found to be dominated by the diffusive behavior having contribution of the form ω−0.5.

Electrical conduction mechanisms and dielectric constants of nanostructured methyl violet 2B thin films

The uniform thin films of methyl violet 2B, MV2B, with thicknesses ranged from 96 to 300 nm, have been successfully prepared by spin coating technique. X-ray diffraction showed that the powder and pristine thin film of MV2B have amorphous structure. The amorphous pristine films become polymorphous nanocrystallites after annealing at 433 K. The electrical properties of MV2B thin films have been studied. There are a number of operational environments where the performance of MV2B thin films is likely to be affected significantly on their electrical properties and dielectric constants such as the differences of film thicknesses, temperatures and frequencies. It was found that the DC conductivity of MV2B films increases with increasing temperature. The extrinsic conduction mechanism is operating in temperature range of 288–360 K with activation energy of 0.16 eV, and the conduction in extrinsic region is explained via applying Mott model for variable range hopping. The intrinsic conduction mechanism is operating in temperatures >360 K with activation energy of 0.91 eV. The conduction in intrinsic region is explained by applying band to band transitions theory. The AC electrical conductivity and dielectric relaxation of MV2B thin films in the temperature range 365–473 K and in frequency range 0.1–100 kHz has been also studied. It has been shown that theoretical curves generated from correlated barrier hopping, CBH, model gives the best fitting with experimental results. Analysis of these results proved that conduction occurs by phonon-assisted hopping between localized states and it is performed by bipolaron hopping mechanism. The temperature and frequency dependence of both the real and imaginary parts of dielectric constant have been investigated.

Magnetic and dielectric studies of Fe substituted sillenite phase bismuth cobaltite nanoparticles

(Bi13Co12)CoO40 (BCO) and (Bi13Co5.5Fe6.5)CoO40 (BCFO) nanoparticles are prepared by sol–gel auto combustion method. The X-ray diffraction study (XRD) reveals cubic crystal structure with space group I23. Surface scanning via atomic force microscopy shows the particle size decreases from 100nm to 75nm on partially substituting Fe at Co site. At room temperature, BCO is paramagnetic and shows signature of magnetic ordering at 30K, which seems to be competing paramagnetic and antiferromagnetic behavior. No sign of magnetic disorder is seen, though indication of magnetic frustration is seen. Interestingly, the Fe substituted BCFO shows large magnetic disorder (even at room temperature) with strengthening ferromagnetic ordering as the temperature is lowered. The low temperature dielectric and magnetodielectric measurement shows dominance of extrinsic contributions, through-out the temperature range for BCO. For BCFO, the behavior may be divided under two regions viz., intrinsic (<260K) and extrinsic (>260K). Relaxation in both the regions is described by Arrhenius behavior with activation energies 0.25eV and 0.04eV in the extrinsic and intrinsic regions respectively. Most interestingly, the dielectric loss decreases by one order for Fe substituted sample. The Haverliak–Negami equation is found to better describe the observed relaxation data.

Electrical and Dielectrical Properties of 0.19Ba(NO3)2 - 0.81KNO3:CeO2 Solid Electrolyte System

The characterization, dc and ac ionic conductivity studies of 0.19Ba(NO3)2 - 0.81KNO3: CeO2 nano dispersed sysyem, σx, has been measured from room temperature to nearly their melting points. At any temperature the maximum enhancement in conductivity occurs at 10.8m/o 0.19Ba(NO3)2 - 0.81KNO3:CeO2. The activation energies are calculated in the extrinsic region of temperature. XRD and DSC indicate that no new structure is formed in the dispersoid material and the melting point is not affected. The gradual increase in conductivity (0.19Ba(NO3)2 - 0.81KNO3:CeO2) is due to the presence of nano CeO2, which interacts with cations, thereby reducing ion pairing and increases the number of charge carriers. The incorporation of nano dispersoid particles not only reduces the interfacial resistance but also provides better enhancement in conductivity.

A Continuous Electrical Conductivity Model for Monolayer Graphene From Near Intrinsic to Far Extrinsic Region

We present a closed-form continuous model for the electrical conductivity of a single layer graphene (SLG) sheet in the presence of short-range impurities, long-range screened impurities, and acoustic phonons. The validity of the model extends from very low doping levels (chemical potential close to the Dirac cone vertex) to very high doping levels. We demonstrate complete functional relations of the chemical potential, polarization function, and conductivity with respect to both doping level and temperature (\(T\) ), which were otherwise developed for SLG sheet only in the very low and very high doping levels. The advantage of the continuous conductivity model reported in this paper lies in its simple form which depends only on three adjustable parameters: the short-range impurity density, the long-range screened impurity density, and temperature \(T\) . The proposed theoretical model was successfully used to correlate various experiments in the midtemperature and moderate density regimes.

Polaron activation energy of nano porphyrin nickel(II) thin films

5,10,15,20-Tetraphenyl-21H, 23H-porphyrin nickel(II), NiTPP films were prepared by thermal evaporation method of mother powder material. Electrical as well as thermo-electric properties were investigated for the as-deposited and annealed NiTPP films. The effect of NiTPP film thickness (160–460 nm) and isochronal annealing in temperature range (300–348 K) on DC electrical properties were studied. Both bulk resistivity and the mean free path were determined; their values are 1.38 × 105 Ω cm and 0.433 nm, respectively. The electrical conductivity exhibits intrinsic and extrinsic conduction. The values of activation energy in extrinsic and intrinsic regions are 0.204 and 1.12 eV, respectively. Mott’s parameters were determined at low temperature. Seebeck coefficient indicates p-type conduction of NiTPP films. Carrier density, mobility and holes concentration were determined. Seebeck coefficient decreases with the increasing of temperature, while the conductivity increases with the increasing of temperature. The difference between the conductivity and the thermoelectric power activation energies was attributed to the potential barrier grain boundaries.

Conductance in Nb6VSb3O25—a new ceramic compound

The electrical measurements performed on Nb6VSb3O25-ceramics showed a sharp increase of the n-type electrical conduction at 330K from the extrinsic region with the activation energy of Ea=0.01eV to the intrinsic one with the activation energy of Ea=0.75eV. At high temperatures, i.e. above 520K, a rather well defined linear slope of diffusion thermopower was found which extrapolates to (0, 0). The I–V characteristics, measured at 300 and 400K, showed a symmetric and non-linear behaviour as well as a broad minimum of the conductance G vs. the applied voltage V, which is being shifted into the higher voltages and simultaneously its value falls with a rise in temperature. These results are interpreted in a framework of deep donor and shallow trap levels as of grain boundaries.

Effects of intrinsic and extrinsic factors on the diet of Bathyraja macloviana, a benthophagous skate

The effects of intrinsic (sex, maturity stage and body size) and extrinsic (depth and region) factors on the diet of Bathyraja macloviana, in the south-west Atlantic Ocean, were evaluated using a multiple-hypothesis modelling approach. Bathyraja macloviana fed mainly on polychaetes followed by amphipods, isopods and decapods. Effects of intrinsic and extrinsic factors on diet composition of this species were found. The consumption of polychaetes had a humped relationship with total length (L(T), and isopods and decapods increased with increasing L(T). Immature individuals preyed on amphipods more heavily than mature individuals. Furthermore, region and depth had an important effect on the consumption of isopods, decapods and amphipods. Such ontogenetic changes and spatial patterns may provide insights into understanding the regulatory mechanisms of marine communities.

Electrical Studies on PZT Ceramic

Polycrystalline sample of PZT (52/48) was prepared by solid-state reaction method. X-ray analysis indicated the formation of single-phase. Electrical and impedance-spectroscopy plots were employed to analyze the electrical behavior of the sample, as a function of frequency, in the range of 0.01 Hz to 1 M Hz at different temperatures. Spectroscopic and complex plots indicated non-Debye dielectric relaxation. Detailed electrical studies revealed that the conduction is through hoping of electrons (extrinsic region) at lowers temperature and migration of oxygen vacancies at high temperature (intrinsic region). The results are explained using Euryod’s conduction model and confirmed with pyroelectric and ferroelectric data.