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Pradeep D.,Indian Institute of Technology Madras | Rawal D.S.,Solid State Physics Laboratory | Karmalkar S.,Indian Institute of Technology Madras
IEEE Transactions on Electron Devices | Year: 2017

The channel mobility, μ0, parasitic source/ drain resistances, RS/RD, and virtual gate length, due to surface traps, at low drain-source bias, VDS, are important parameters of high-electron mobility transistors (HEMT's). DC methods are available to extract these parameters from drain-current, ID, versus gate-source voltage, VGS, measurements. We report a comparative study of two such methods based on the linear ID -VGS approximation, from the viewpoint of device modeling, process monitoring, and physical understanding.Onemethod yields constant values of μ0 and RS + RD averaged over the VGS range, while the other yields variations of μ0, RS, RD, and with VGS. The study reveals some new details of these methods, and discusses their results on a range of GaAs andGaN HEMTs.

Saxena A.,Center for Fire Explosive and Environment Safety | Srivastava A.K.,Canadian Department of National Defence | Singh B.,Canadian Department of National Defence | Goyal A.,Solid State Physics Laboratory
Journal of Hazardous Materials | Year: 2012

Silica nanoparticles of diameter, 24-75nm and surface area, 875m 2/g were synthesized using aero-gel route. Thereafter, nanoparticles were impregnated with reactive chemicals, and used as reactive adsorbent to study the removal of toxic nerve and blister chemical warfare agents and their simulants from solutions. Trichloroisocyanuric acid impregnated silica nanoparticles showed the best performance and indicated physisorption followed by chemisorption/degradation of toxicants. This indicated their suitability as universal decontaminant for nerve and blister agents. This system showed a decrease in t 1/2 from 1210 to 2.8min for the removal of king of chemical warfare agents, i.e., sulphur mustard. Hydrolysis, dehydrohalogenation and oxidation reactions were found to be the route of degradation of toxicants over impregnated silica nanoparticles. © 2011 Elsevier B.V..

Goyal N.,Norwegian University of Science and Technology | Saxena R.S.,Solid State Physics Laboratory
IEEE Electron Device Letters | Year: 2013

We propose a new laterally diffused metal-oxide-semiconductor field-effect transistor (LDMOSFET) with a tunneling junction at the drain side to reduce its on-state resistance and improve the peak transconductance significantly, as compared with the conventional LDMOSFET device. Using 2-D numerical simulations in an ATLAS device simulator, we have shown that the proposed tunneling junction at the drain side results in 25% reduction in RON and 20% improvement in peak transconductance in an ∼ 40-V device without any significant degradation in other performance parameters. © 2012 IEEE.

Pahuja P.,University of Delhi | Prakash C.,Solid State Physics Laboratory | Tandon R.P.,University of Delhi
Ceramics International | Year: 2014

In this paper, effect of addition of Ni0.8Co 0.2Fe2O4 (NCF), prepared by three different methods namely solid state reaction method, sol-gel and co-precipitation, has been studied on microstructural, magnetic, dielectric, ferroelectric and magnetoelectric properties of multiferroic composite system 0.95 Ba 0.95Sr0.05TiO3-0.05 Ni0.8Co 0.2Fe2O4. Ba0.95Sr 0.05TiO3 (BST) has been prepared by solid state reaction method. Titular representation of NCF samples prepared by sol-gel, co-precipitation, solid state reaction method is N-SG, N-CP, N-SS respectively and that of corresponding magnetoelectric composite is C-SG, C-CP, C-SS. X-ray diffraction analysis of the composite samples (C-SG, C-SS, C-CP) indicated the presence of both NCF and BST phases. Rietveld analysis of XRD pattern further confirmed the proper phase formation in the composite samples. Sol-gel and co-precipitation processes result in finer NCF particles as confirmed by Transmission electron microscopy (TEM). Sample N-SG possesses uniform particle size and shape. Magnetization versus magnetic field (M-H) loops of samples C-SS and C-CP possess respectively highest value of remanant magnetization and magnetic coercive field. Dielectric properties of BST, NCF and composite samples have been measured in the frequency range of 20 Hz-1 MHz and temperature range of 50-170 C. The composite sample C-CP results in highest value of dielectric constant in comparison to samples C-SS and C-SG. Polarization versus electric field (P - E) measurements pointed that composite sample C-SG possesses highest value of remanant and saturation polarization and C-SS possesses lowest value of coercive electric field. The composite sample C-SS possesses highest value of magnetoelectric coefficient. © 2013 Elsevier Ltd and Techna Group S.r.l.

Saxena R.S.,Solid State Physics Laboratory | Kumar M.J.,Indian Institute of Technology Delhi
IEEE Transactions on Electron Devices | Year: 2012

We propose a new trench gate power MOSFET with poly-Si spacers formed in the trench to work as gate material. This approach reduces the total gate charge and gate-to-drain capacitive coupling without affecting any other device performance parameter. Using 2-D numerical simulation on a ∼ 25-V trench gate MOSFET, we have shown that using a 50-nm-wide spacer gate in a 1 μm × 1 μm trench may give >40% reduction in the gate-to-drain charge compared with the conventional device. The proposed technique has been shown to be better than the other techniques proposed earlier for reducing gate charge as it does not affect the gate control of the accumulation region charge or any other performance parameter, e.g., breakdown voltage, and can be implemented along with any of the existing techniques. © 2011 IEEE.

Kumar A.,Indian Institute of Technology Delhi | Vinayak S.,Solid State Physics Laboratory | Singh R.,Indian Institute of Technology Delhi
Current Applied Physics | Year: 2013

Micro-structural investigation of Ni/GaN Schottky barrier diodes has been carried out using high-resolution transmission electron microscopy and electron diffraction spectrum in order to emphasize the role of Ni/GaN interface in controlling the Schottky diode behavior. Variable temperature Hall effect measurement of GaN samples along with the current-voltage (I-V) characteristics of Ni/n-GaN Schottky barrier diodes have been measured in 100-380 K temperature range. Results are analyzed in terms of thermionic emission theory by incorporating the concept of barrier inhomogeneity at the metal/semiconductor interface. The observed anomaly of temperature dependence of Schottky barrier height and ideality factor are explained by invoking two sets of Gaussian distribution of SBH in the temperature ranges of 100-180 K and 220-380 K, respectively. The value of A** (effective Richardson constant) as determined from the modified Richardson plot is 29.2 A/(cm2 K 2), which shows an excellent agreement with the theoretical value (26.4 A/(cm2 K2)) in the temperature range of 220-380 K. © 2013 Elsevier B.V. All rights reserved.

Rachna S.,Raja Ramanna Center for Advanced Technology | Bhattacharyya S.,Solid State Physics Laboratory | Gupta S.M.,Raja Ramanna Center for Advanced Technology
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2010

A correlated study involving structure analysis, temperature dependence of dielectric functions and the complex impedance spectroscopy analysis was carried out in lanthanum modified bismuth titanate (BT, Bi 4-xLa xTi 3O 12; x = 0, 0.75) ceramics. A series addition of three RQ circuits has been shown to remarkably fit the complex impedance data for both x = 0 and 0.75 samples, which were attributed to crystalline layer, plate boundary and grain boundary microelements. Temperature dependence DC-conductance of these microelements has revealed that lanthanum-ion substitution is mainly taking place in the perovskite blocks, which also led to decrease in orthorhombic splitting. This site preferred substitution was also consistent with shift in the oxygen ion-jump relaxation peak in the temperature dependence of the dissipation factor study. © 2010 Elsevier B.V.

Laishram R.,Solid State Physics Laboratory | Thakur O.P.,Solid State Physics Laboratory | Bhattacharya D.K.,Solid State Physics Laboratory
Materials Letters | Year: 2011

Highly dense, good quality microwave dielectrics based on Mn4+ doped ZST have been prepared with ZST nanopowder without using any sintering aid. Single phase orthorhombic crystalline structure has been confirmed by XRD pattern. The room temperature dielectric constant remains almost unchanged in the low and microwave frequency regions (1 MHz to 9.3 GHz). A significant change in the microwave dielectric properties of ZST ceramics was observed with increasing Mn4+. There was almost four times increase in quality factor with Mn4+ doping in ZST ceramics. © 2011 Elsevier B.V.

The structural and electrical properties of chemical-solution-deposited Bi1 - xSmxFeO3 (x = 0, 0.025, 0.05, 0.075, 0.1) thin films on Pt/Ti/SiOx/Si (100) substrates were investigated. Films up to 5 at.% Sm exhibited a single perovskite phase with rhombohedral structure, whereas films with 7.5 and 10 at.% Sm exhibited a distorted orthorhombic crystal structure. Atomic force microscopy of the films showed homogeneous and smooth surface. Films with 7.5 at.% Sm exhibited significant reduction in leakage current in the high electric field region and improved breakdown characteristic. The polarization vs. electric field (P-E) hysteresis loops were recorded in a 100 nm thick film with 3 V coercive voltages. Moreover, well saturated P-E hysteresis loops with high polarization (80 μC/cm 2) and low coercive field (300 kV/cm) were also recorded in 100 nm thick films with low coercive voltage (5 V). The Sm-substitution in BiFeO 3 improved the fatigue endurance with no significant degradation in polarization even after 108 fatigue cycles. These results demonstrate that Sm-substituted BifeO3 films have potential for application in low voltage operational device. © 2012 Elsevier B.V.

Nenavathu B.P.,Indian Institute of Technology Roorkee | Krishna Rao A.V.R.,Indian Institute of Technology Roorkee | Goyal A.,Solid State Physics Laboratory | Kapoor A.,Solid State Physics Laboratory | Dutta R.K.,Indian Institute of Technology Roorkee
Applied Catalysis A: General | Year: 2013

Se doped ZnO nanoparticles (NPs) were successfully synthesized by thermo-mechanical method whose band gap increased with concentration of Se doping. Transmission electron microscopy of 5 wt% Se doped ZnO NPs revealed spherical nanoparticles of average size of 9.5 nm. X-ray photoelectron spectroscopy (XPS) revealed Se 3d binding energy at 59.5 eV, confirmed SeO 2 in the doped ZnO NPs. Fluorescence emission spectroscopy of Se doped ZnO NPs revealed oxygen vacancies which increased with the concentration of Se doping. The photodegradation efficiency of trypan blue (TB) using 30 W UV lamp was higher for Se doped ZnO NPs than pristine ZnO NPs, depended on Se doping concentrations, UV illumination, concentrations of photocatalyst and pH of the dye solution. The batch of 0.6 mg of 5 wt% Se doped in ZnO NPs per mL of TB dye maintained at pH 5 exhibited maximum photodegradation efficiency (89.2 ± 3.1%). Higher photocatalytic degradation efficiency for Se doped ZnO NPs was correlated with incorporation of oxygen vacancies due to Se doping, which were likely intermediate levels for transiting photoexcited charge carriers for generation of hydroxyl radicals and consequently facilitated photodegradation. Terephthalic acid assay confirmed formation of hydroxyl radicals in dye solution treated with photocatalyst. © 2013 Elsevier B.V. All rights reserved.

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