Department of Electrical Engineering

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Investigations were carried out on the ambient condition oxidation of self-assembled, fairly uniform indium nitride (InN) quantum dots (QDs) fabricated on p-Si substrates. Incorporation of oxygen in to the outer shell of the QDs was confirmed by the results of transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS). As a consequence, a weak emission at high energy (∼1.03eV) along with a free excitonic emission (0.8eV) was observed in the photoluminescence spectrum. The present results confirm the incorporation of oxygen into the lattice of the outer shell of InN QDs, affecting their emission properties. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

World University root node

Physica Status Solidi (B) Basic Research

Evidences for ambient oxidation of indium nitride quantum dots

Phase pure wurtzite GaN films were grown on Si (100) substrates by introducing a silicon nitride layer followed by low temperature GaN growth as buffer layers. GaN films grown directly on Si (100) were found to be phase mixtured, containing both cubic () and hexagonal () modifications. The x-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN films grown with silicon nitride buffer layer grown at 800 C when compared to the samples grown in the absence of silicon nitride buffer layer and with silicon nitride buffer layer grown at 600 C. Core-level photoelectron spectroscopy of SixNy layers reveals the sources for superior qualities of GaN epilayers grown with the high temperature substrate nitridation process. The discussion has been carried out on the typical inverted rectification behavior exhibited by n-GaNp-Si heterojunctions. Considerable modulation in the transport mechanism was observed with the nitridation conditions. The heterojunction fabricated with the sample of substrate nitridation at high temperature exhibited superior rectifying nature with reduced trap concentrations. Lowest ideality factors (∼1.5) were observed in the heterojunctions grown with high temperature substrate nitridation which is attributed to the recombination tunneling at the space charge region transport mechanism at lower voltages and at higher voltages space charge limited current conduction is the dominating transport mechanism. Whereas, thermally generated carrier tunneling and recombination tunneling are the dominating transport mechanisms in the heterojunctions grown without substrate nitridation and low temperature substrate nitridation, respectively. © 2011 American Institute of Physics.

Fulltext

Journal of Applied Physics

Substrate nitridation induced modulations in transport properties of wurtzite GaNp-Si (100) heterojunctions grown by molecular beam epitaxy

Non-polar a-plane GaN films were grown on an r-plane sapphire substrate by plasma assisted molecular beam epitaxy (PAMBE). The effect of growth temperature on structural, morphological and optical properties has been studied. The growth of non-polar a-plane (1 1 -2 0) orientation of the GaN epilayers were confirmed by high resolution X-ray diffraction (HRXRD) study. The X-ray rocking curve (XRC) full width at half maximum of the (1 1 -2 0) reflection shows in-plane anisotropic behavior and found to decrease with increase in growth temperature. The atomic force micrograph (AFM) shows island-like growth for the film grown at a lower temperature. Surface roughness has been decreased with increase in growth temperature. Room temperature photoluminescence shows near band edge emission at 3.4343.442 eV. The film grown at 800 °C shows emission at 2.2 eV, which is attributed to yellow luminescence along with near band edge emission. © 2010 Elsevier B.V. All rights reserved.

Journal of Crystal Growth

Growth temperature induced effects in non-polar a-plane GaN on r-plane sapphire substrate by RF-MBE

We have grown Ga deficient GaN epitaxial films on (0001) sapphire substrate by plasma-assisted molecular beam epitaxy and report the experimental evidence of room temperature ferromagnetic behavior. The observed yellow emission peak in room temperature photoluminescence spectra and the peak positioning at 300 cm-1 in Raman spectra confirms the existence of Ga vacancies. The x-ray photoelectron spectroscopic measurements further confirmed the formation of Ga vacancies; since the N/Ga is found to be 1. The ferromagnetism is believed to originate from the polarization of the unpaired 2p electrons of N surrounding the Ga vacancy. © 2011 American Institute of Physics.

Applied Physics Letters

Experimental evidence of Ga-vacancy induced room temperature ferromagnetic behavior in GaN films

The electrical transport behavior of n - n indium nitride nanodot-silicon (InN ND-Si) heterostructure Schottky diodes is reported here, which have been fabricated by plasma-assisted molecular beam epitaxy. InN ND structures were grown on a 20nm InN buffer layer on Si substrates. These dots were found to be single crystalline and grown along [0 0 0 1] direction. Temperature-dependent current density-voltage plots (J - V - T) reveal that the ideality factor (N) and Schottky barrier height (SBH) (φB) are temperature dependent. The incorrect values of the Richardson constant (A * *) produced suggest an inhomogeneous barrier. Descriptions of the experimental results were explained by using two models. First one is barrier height inhomogeneities (BHIs) model, in which considering an effective area of the inhomogeneous contact provided a procedure for a correct determination of A * *. The Richardson constant is extracted ∼110A cm -2 K -2 using the BHI model and that is in very good agreement with the theoretical value of 112A cm -2 K -2. The second model uses Gaussian statistics and by this, mean barrier height φ 0 and A * * were found to be 0.69eV and 113A cm -2 K -2, respectively. Copyright © 2011 Mahesh Kumar et al.

Journal of Nanomaterials

Barrier inhomogeneity and electrical properties of InN Nanodots/Si heterojunction diodes

This paper proposes a protection scheme based on Wavelet Multi Resolution Analysis and Artificial Neural Networks which detects and classifies various faults like Single phasing, Under voltage, Unbalanced supply, Stator Turn fault, Stator Line to Ground fault, Stator Line to Line fault, Broken bars and Locked rotor of a three-phase induction motor. The three phase Induction Motor is represented by a universal model which is valid for a wide range of frequencies. The same has been simulated using MATLAB/Simulink software and tested for various types of motor faults. The wavelet decomposition of three-phase stator currents is carried out with Bi-Orthogonal 5.5 (Bior5.5). The maximum value of the absolute peak value of the highest level (d1) coefficients of three-phase currents is defined as fault index which is compared with a predefined threshold to detect the fault. The normalized fourth level approximate (a4) coefficients of these currents are fed to a Feedforward neural network to classify various faults. The normalized peak d1 coefficients of three-phase currents are fed to another Feedforward neural network to identify the faulty phase of stator internal faults. The algorithm has been tested for various incidence angles and proved to be simple, reliable and effective in detecting and classifying the various faults and also in identifying the faulty phase of stator. © 2011 IEEE.

Proceedings - 2011 Annual IEEE India Conference: Engineering Sustainable Solutions, INDICON-2011

Wavelet - ANN based fault diagnosis in three phase induction motor

Optimizing Gain of an RF Amplifier using Design of Experiments (DOE), is presented. The constraints of keeping minimum deviations in both frequency and Noise Figure (NF) is taken in to account by ANOVA and nominal-the-best approach of Taguchi Methods. Gain of the amplifier is improved by 2.4 dB with frequency and NF deviations of 0% each. © 2011 IEEE.

2011 International Symposium on Integrated Circuits, ISIC 2011

Optimizing Gain of 5 GHz RF amplifier keeping minimum deviation in center frequency and noise figure

The paper presents a novel model for loss less video compression. In this paper we propose some mathematical models, using cartesian co-ordinate system, that can be used for prediction. The models are based on our novel approach of explanation to the working principle of Median Edge Director(MED). Experiments have been carried out with these models and based on their performance, one of the models has been considered for the prediction scheme. Performance of the proposed prediction scheme is same as that of the standard motion compensation but at a very low complexity. © 2011 IEEE.

School of Liberal Arts (SoLA)

Data Compression Conference Proceedings

A novel prediction model for lossless video compression

Soluble alternating copolymers of N-(3,4,5-tri-n-dodecyloxyphenyl) dithieno[3,2-b:2′,3′-d]pyrrole donor groups and 2,3-di-n- decylquinoxaline, 2,3-di-n-decylpyrido[3,4-b]pyrazine, 2,3,6,7-tetrakis(n- decyloxy)benzo[a,c]phenazine, or 2,3,6,7-tetrakis(n-decyloxy)dibenzo[f,h] pyrido[4,3-b]quinoxaline acceptors were synthesised using Stille coupling reactions. Experimental absorption maxima in THF range from 645 to 770 nm. These optical data, along with the results of quantum-chemical calculations and electrochemical measurements, show that, as expected, the pyridopyrazine moiety acts as a stronger acceptor than quinoxaline and that the extended species benzophenazine and dibenzopyridoquinoxaline are stronger acceptors than quinoxaline and pyridopyrazine, respectively. Modest average hole mobilities of up to ca. 3.0 × 10-4 cm2 V-1 s -1 were obtained in field-effect transistors. Bulk heterojunction photovoltaic devices made from blends of the benzo[a,c]phenazine-based polymer with 3′-phenyl-3′H-cyclopropa[1,9](C60-I h)[5,6]fullerene-3′-butanoic acid methyl ester (1:3 weight ratio) exhibited average power conversion efficiencies up to 1.4%. © The Royal Society of Chemistry 2011.

Journal of Materials Chemistry

Dithienopyrrole-quinoxaline/pyridopyrazine donor-acceptor polymers: Synthesis and electrochemical, optical, charge-transport, and photovoltaic properties

This paper presents the design and experimental evaluation of fast output sampling feedback controller to minimize structural vibration of a cantilever beam using Shape Memory Alloy (SMA) wires as control actuators and piezoceramics as sensor and disturbance actuator. Linear dynamic models of the smart cantilever beam are obtained using online recursive least square parameter estimation. A digital control system that consists of Simulink™ modeling software and dSPACE DS1104 controller board is used for identification and control. The effectiveness of the controller is shown through simulation and experimentation by exciting the structure at resonance.