Department of Physics

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Physics

We report on the effect of Ni and NiO interlayers on an indium oxide-doped ZnO (IZO)-based ohmic scheme for a transparent and low resistance contact to the p-GaN. Ni/IZO and NiO/IZO contact layers on p-GaN yielded very low specific contact resistances of 9.2 × 10-5 and 3.6 × 10 -5 Ω cm2, respectively, after annealing at 500°C for 1 min under a nitrogen ambient. Auger electron spectroscopy and X-ray photoemission spectroscopy analysis of the IZO and p-GaN interface indicated that Ga atoms out-diffused and the NiO phase was formed at the interface region after the thermal annealing process, resulting in a decrease in contact resistance. © 2005 The Electrochemical Society. All rights reserved.

World University root node

School of Advanced Sciences

Chennai Campus

Journal of the Electrochemical Society

Effect of interlayers on the indium oxide-doped ZnO ohmic contact to p-type GaN

A high quality reflective vertical surface is required for various optical micro electro mechanical system (MEMS) devices. In this paper, we discuss an extensive investigation of TiAu sputtering, with respect to temperature, pressure, and electric power input, followed by rapid thermal annealing (RTA) to improve the adhesion and reflection characteristics of a vertical micromirror. The vertical surface was fabricated by means of the deep reactive ion etching (DRIE) process of a silicon-on-insulator (SOI) wafer, with an 80-μm -thick layer of Si. Then, 20-nm -thick Ti and 200-nm -thick Au films were deposited on the vertical surface as adhesion and reflective layers, respectively, using rf/dc magnetron sputtering. The Au films were deposited at room temperature (20 °C) and annealed at 380 °C for 30 s in a RTA chamber. While taking into consideration the conformability and the reflectance of the Au vertical mirror, the process conditions were optimized at an argon pressure of 10 mTorr and an electric power input of 300 W. The best surface roughness obtained was 7 nm (rms) for a useful upper sidewall with a reflectance of 97.5% in the IR (Infrared) range (1500 nm-1600 nm). © 2005 American Vacuum Society.

Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures

Conformability and optical reflectance of TiAu film sputtered on the Si vertical sidewalls

Emission of hydrocarbon at low temperature, especially in the cold start condition of the automobile engine, has attracted attention these days. For the first time an electrochemical sensor based on LaGaO3 with iron doping was demonstrated to have very high sensitivity to propene (C3H 6) at low temperature (423-573 K). In the amperometric mode, the output current signal was found to increase linearly with the C 3H6 concentration (500-2000 ppm) in logarithm scale. Effect of iron doping at the gallium site was found to influence the sensing properties greatly and the electrolyte composition La0.7Sr 0.3Ga0.7Fe0.3O3 showed the highest sensitivity of 976 μA/decade at 473 K. The sensors were fast, reproducible and highly selective to hydrocarbons. © 2004 Elsevier B.V. All rights reserved.

Sensors and Actuators, B: Chemical

Amperometric hydrocarbon sensor using La(Sr)Ga(Fe)O3 solid electrolyte for monitoring in exhaust gas

Near-field patterns of uniplanar compact photonic bandgap (UC-PBG) and non-UCPBG finite-width conductor-backed co-planar waveguides (FW-CBCPWs) are characterized using an electro-optic near-field mapping system. This system is very effective in visually showing the role of the UC-PBG structure in the suppression of microstriplike (MSL) modes in the FW-CBCPWs. © 2005 Wiley Periodicals, Inc.

Microwave and Optical Technology Letters

Investigation of microstriplike mode suppression in UC-PBG FW-CBCPW by using an electro-optic near-field characterization

We implemented all-fiber delay line using linearly chirped fiber Bragg gratings (CFBG), which can be applicable for reflectometry or optical coherence tomography (OCT). Compared with the previously reported delay lines, the proposed fiber-based optical delay line has in principle novel advantages such as automatic dispersion cancellations without additional treatment and a gain in optical delay that is dependent on parameters of used CFBGs. Dispersion compensation in optical delay line (ODL), which is the indispensable problem in bulk optics based ODL, is demonstrated in fiber by using two identical but reversely ordered CFBGs. Amplified variable optical delay of around 2.5 mm can be obtained by applying small physical stretching of one of CFBGs in the proposed scheme. The operational principles of the all-fiber variable optical delay line, which are based on the distributed reflection characteristic of a CFBG employed, are described. Especially properties such as in-line automatic dispersion cancellation and amplified optical delay under strain are dealt. To demonstrate the properties of the proposed scheme, which is theoretical consequences under assumptions, an all-fiber optical delay line have been implemented using fiber optic components such as fiber couplers and fiber circulators. With the implanted ODL, the group delay and amplified optical delay length was measured with/without strain. The wavelength independent group delay measured within reflection bandwidth of the CFBG has proved the property of automatic dispersion cancellations in the proposed fiber delay line. Optical delay length of 2.5 mm was obtained when we apply small physical stretching to the CFBG by 100 μm and this is expressed by the amplification factor of 25. Amplification factor 25, which is less than theoretical value of 34 due to slipping of fiber in the fiber holder, shows that the proposed scheme can provide large optical delay with applying small physical stretching to the CFBG. We measure slide glass thickness to check the performance of the fiber delay line and the good agreement in measured and physical thickness of slide glass (∼1 mm thick) validates the potential of proposed delay line in the applications of optical reflectometry and OCT. We also discuss the problem and the solution to improve the performance. Copyright © 2005 the institute of electronics, information and communication engineers.

IEICE Transactions on Electronics

Implementation of an all-fiber variable optical delay line with a pair of linearly chirped fiber Bragg gratings

An electrooptic field-mapping system based on a gain-switched distributed feedback (DFB) pulsed laser and a CdTe electrooptic crystal is used for characterizing near-field patterns of conventional and uniplanar compact photonic band gap (UC-PBG) finite-width conductor-backed coplanar waveguides (FW-CBCPWs). Comparison of near-field patterns of the FW-CBCPWs visually shows that microstrip-like (MSL) modes in the FW-CBCPW are effectively suppressed by using the UC-PBG pattern on the side-ground plates.

35th European Microwave Conference 2005 - Conference Proceedings

Characterization of near-field patterns of a novel UC-PBG FW-CBCPW by using an electrooptic field-mapping technique

We have implemented an all-fiber optical delay line using two linearly chirped fiber Bragg gratings cascaded in reverse order and all-fiber optics components. The features of the proposed all-fiber based technique for variable delay line are discussed theoretically and demonstrated experimentally. The non-invasive cross-sectional images of biomedical samples as well as a transparent glass plate obtained with implemented all-fiber delay line having the axial resolution of 100 μm and the dynamic range of 50dB are presented to validates the imaging performance and demonstrate the feasibility of the delay line for optical coherence tomography. © 2005 Optical Society of America.

Fulltext

Optics Express

All-fiber variable optical delay line for applications in optical coherence tomography: Feasibility study for a novel delay line

A solid-state amperometric NO sensor was investigated. High sensitivity was observed with the sensor consisting of La0.5Sr0.5MnO 3 and La0.4Sr0.6Mn0.8Ni 0.2O3 as inactive and active electrodes to NO oxidation, respectively, and La0.8Sr0.2Ga0.8Mg 0.1Ni0.1O3 as electrolyte. The sensor characteristics were studied in the temperature range 773-973 K and the highest sensitivity was found above 1800 μA/decade at 823 K. Because the current output of this sensor was little affected by coexisting gases, e.g., CO, H 2, C3H6, CO2, H2O, and NO2, it is expected that this sensor can detect NO in exhaust gas selectively. © 2005 The Electrochemical Society. All rights reserved.

Electrochemical and Solid-State Letters

Sensitive amperometric NO sensor using LaGaO3-based oxide ion conducting electrolyte

For the first time, an amperometric electrochemical sensor based on LaGaO3 was demonstrated as highly sensitive to detect hydrocarbon (C3H6) at low temperature (423-773 K). At this temperature range, it is very important to estimate hydrocarbon pollution of automobile exhaust gas (the cold start condition). In the present study, using La 0.5Sr0.5-MnO3 as the oxygen reduction electrode, various hydrocarbon (C3H6) oxidation electrodes of Pt-based alloy systems were investigated. Addition of Co and subsequently cermet LDC [(CeO2)0.8(LaO1.5)0.2] produced very high sensor response and improved the performance of the sensor with respect to that using only Pt paste as the electrode. The sensors were hardly influenced by the oxygen concentration variation (0.5-5%). At the best operating temperature (623 K) the C3H6 sensitivity was above 800 μA/decade, and the lowest temperature of detection was 423 K. The sensors were fast, highly selective in the presence of coexisting gases, e.g., NO, NO2, CO, and H2, in the exhaust, and stable too. Sensors studied in the potentiometric mode and with impedance analysis of the hydrocarbon oxidation electrodes revealed the importance of the electrolyte/electrode interface and the related sensing mechanism.

Chemistry of Materials

An amperometric solid-state gas sensor using a LaGaO3-based perovskite oxide electrolyte for detecting hydrocarbon in exhaust gas. A bimetallic anode for improving sensitivity at low temperature

We report on the indium-oxide-doped ZnO (IZO) transparent ohmic contact to the p-GaN. The IZO transparent ohmic contact layer was deposited on p-GaN by e-beam evaporation. The transmittance of an IZO film with a thickness of 250 nm was 84%-92% for the light in the wavelength range of 400 and 600 nm. In addition, the IZO contact film yielded a low specific contact resistance of 3.4× 10-4 Ω cm2 on p-GaN when annealed at 600 °C for 5 min under a nitrogen ambient. Auger electron spectroscopy and x-ray photoemission spectroscopy analyses of the IZO and p-GaN interface indicated that Ga atoms had out-diffused and an InN phase was formed at the interface region after the thermal annealing process, resulting in a decrease in contact resistance. The light output power of a light-emitting diode (LED) with an IZO ohmic contact layer was increased by 34% at 83 mW of electrical input power compared to that of a LED with a NiAu ohmic contact layer. © 2004 American Institute of Physics.