Department of Electrical Engineering

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InN quantum dots (QDs) were fabricated on silicon nitride/Si (111) substrate by droplet epitaxy. Single-crystalline structure of InN QDs was verified by transmission electron microscopy, and the chemical bonding configurations of InN QDs were examined by x-ray photoelectron spectroscopy. Photoluminescence measurement shows a slight blue shift compared to the bulk InN, arising from size dependent quantum confinement effect. The interdigitated electrode pattern was created and current-voltage (I-V) characteristics of InN QDs were studied in a metal-semiconductor-metal configuration in the temperature range of 80-300 K. The I-V characteristics of lateral grown InN QDs were explained by using the trap model. © 2011 American Institute of Physics.

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Applied Physics Letters

Temperature dependent transport studies in InN quantum dots grown by droplet epitaxy on silicon nitride/Si substrate

Negative differential capacitance (NDC) has been observed in n-GaN/p-Si heterojunctions grown by plasma assisted molecular beam epitaxy (PAMBE). The NDC is observed at low frequencies 1 and 10 kilohertz (kHz) and disappeared at a higher testing frequency of 100 kHz. The NDC is also studied with temperature and found that it has disappeared above 323 °C. CurrentVoltage (IV) characteristics of n-GaN /p-Si heterojunction were measured at different temperatures and are attributed to the space-charge-limited current (SCLC). A simple model involving two quantum states is proposed to explain the observed NDC behavior. © 2010 Elsevier Ltd. All rights reserved.

Solid State Communications

Negative differential capacitance in n-GaN/p-Si heterojunctions

The electrical transport properties of InN/GaN heterostructure based Schottky junctions were studied over a wide temperature range of 200500 K. The barrier height and the ideality factor were calculated from currentvoltage (IV) characteristics based on thermionic emission (TE), and found to be temperature dependent. The barrier height was found to increase and the ideality factor to decrease with increasing temperature. The observed temperature dependence of the barrier height indicates that the Schottky barrier height is inhomogeneous in nature at the heterostructure interface. Such inhomogeneous behavior was modeled by assuming the existence of a Gaussian distribution of barrier heights at the heterostructure interface. © 2011 Elsevier Ltd. All rights reserved.

Barrier height inhomogeneities in InN/GaN heterostructure based Schottky junctions

GaN films were grown on c-plane sapphire by plasma-assisted molecular beam epitaxy (PAMBE). The effect of N/Ga flux ratio on structural, morphological, and optical properties was studied. The dislocation density found to increase with increasing the N/Ga ratio. The surface morphology of the films as seen by scanning electron microscopy shows pits on the surface and found that the pit density on the surface increases with N/Ga ratio. The room temperature photoluminescence study reveals the shift in band-edge emission toward the lower energy with increase in N/Ga ratio. This is believed to arise from the reduction in compressive stress in the films as is evidenced by room temperature Raman study. The transport studied on the Pt/GaN Schottky diodes showed a significant increase in leakage current with an increase in N/Ga ratio and was found to be caused by the increase in pit density as well as increase in dislocation density in the GaN films. © 2011 American Institute of Physics.

Journal of Applied Physics

Effect of N/Ga flux ratio on transport behavior of Pt/GaN Schottky diodes

One of the scientific challenges of growing InN quantum dots (QDs), using Molecular beam epitaxy (MBE), is to understand the fundamental processes that control the morphology and distribution of QDs. A systematic manipulation of the morphology, optical emission, and structural properties of InN/Si (111) QDs is demonstrated by changing the growth kinetics parameters such as flux rate and growth time. Due to the large lattice mismatch, between InN and Si (∼8%), the dots formed from the Strannski-Krastanow (S-K) growth mode are dislocated. Despite the variations in strain (residual) and the shape, both the dot size and pair separation distribution show the scaling behavior. We observed that the distribution of dot sizes, for samples grown under varying conditions, follow the scaling function. © 2010 Springer Science+Business Media B.V.

Journal of Nanoparticle Research

Kinetics of self-assembled InN quantum dots grown on Si (111) by plasma-assisted MBE

This paper presents stochastic convergence analysis of particle swarm optimization algorithm involving randomness and applying the results to the Analog RF Circuits to optimize the circuit parameters. In every iteration, each particle position is represented as vector and the standard particle swarm algorithm determined by positive real tipple {w,c 1,c 2}. Comparisons for convergence are presented with respect to fixed tipple {w,c 1,c 2} and random tipple {w,c 1,c 2}. Various results show that the randomness in defining new position to particle leads to better convergence property. Also, exploration and exploitation trade off are discussed with examples. It is demonstrated that each particle undergoes both exploration and exploitation in convergence process; if the randomness in the particle generation is considered. The parameters considered for RF circuit are cutoff frequency, Phase Noise and Signal to Noise Ratio (SNR). Results are compared between both fixed values and random values of parameters in convergence analysis of PSO. © 2011 IEEE.

Proceedings of the 2011 World Congress on Information and Communication Technologies, WICT 2011

Optimization of analog RF circuit parameters using randomness in particle swarm optimization

In this paper, wavelet transform technique is applied to detect fault in the transmission line with flexible alternating current transmission (FACTS) device. Presence of FACTS device changes the system impedance and hence makes it difficult to detect faults on the line which may result into maloperation of relay. Three phase currents are monitored at both ends of the transmission line using global positioning system synchronizing clock. Wavelet transforms, which is very fast and sensitive to high frequency signal is used to extract transients in these line currents for fault detection. Fault index is calculated based on the sum of local and remote end detail coefficients and compared with threshold value to detect the fault. Proposed technique is tested for various faults and fault inception angles with and without static synchronous compensator (STATCOM) device. Simulation results are presented showing the selection of proper threshold value for fault detection. © 2011 IEEE.

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

Detection of transmission line faults in the presence of STATCOM using wavelets

We consider the role of independent single antenna relays in allowing for interference cancellation and for multiplexing of uplink and downlink communications, in the presence of multiple interfering users. For a specific practical scenario of interest, we construct interference neutralization schemes that are simple, distributed and which encode over both space and time, to achieve performance improvements over basic TDMA schemes. These improvements are quantified in terms of the achievable degrees of freedom (DOF), where asymptotic analysis reveals that in specific cases, these simple techniques achieve optimal DOF performance. {\textcopyright} 2011 IEEE.

2011 Information Theory and Applications Workshop, ITA 2011 - Conference Proceedings

Interference neutralization for separated multiuser uplink-downlink with distributed relays

A set of test structures for in situ stress measurement is presented. The test structures were realized by means of surface micromachining, adopting photoresist as sacrificial layer and electroplated gold as structural layer. Initially array of buckling type test structures cantilevers, fixed-fixed beams, guckel rings and diamond were used to find out critical buckling beam. Later on rotational type pointer, double indicator and long-short beam strain sensor were analyzed to find out stress. Stress measurement techniques using micromachined structures are compared with the wafer curvature technique. Analytical calculations of the fabricated structures were performed for plated gold, the values of residual stress is found between 100 and 150MPa.

Technical Proceedings of the 2011 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2011

Fabrication and analysis of MEMS test structures for residual stress measurement

Unlike image quality, video quality is affected by the temporal factor, in addition to the spatial one. In this paper, we investigate into the impact of both the factors on the overall perceived video quality and combine them into a metric. We use machine learning as a tool to study and analyze the relationship between the factors and the overall perceived video quality. It is shown that apart from their individual contributions, the interaction of the two factors also plays a role in determining the overall video quality. We report the experimental results and the related analysis using videos from two publicly available databases. © 2011 IEEE.