Rama Venkat

Energy Efficient RGBW Pixel Configuration for Light-Emitting Displays

A study on LED displays has been conducted exploring a more efficient method for color generation than the traditional method. The study is comprehensive and thoroughly performed employing various sets of experiments in order to examine the functionality of the new proposed scheme which includes a literature review, theoretical modeling based on a scientific study, experimental data measurements of a developed prototype, and statistical data based on a survey. This study resulted in very interesting outcomes that may lead to a tremendous change in the existing LED display technology.

Modeling of Porous Alumina Template Formation under Constant Current Conditions

Anodized alumina templates have emerged as an important material system for the low-cost fabrication of semiconductor and metal nanostructure arrays. This material system uses natural self-organization for the creation ofperiodic arrays of nanoscale structures. In spite of the extensive experimental investigations reported in the literature, the theoretical mechanisms, and their dependence on process parameters such as current density and electrolytes, are not well understood. In this article, we propose a theoretical model based on the rate equation approach in which both the alumina formation and etching are considered. This model employs a minimal number of parameters and yet captures the essence of the experimental observations with sulfuric acid as the electrolyte and can be used as a predictive tool for process selection.

A model for thermal growth of ultrathin silicon dioxide in O/sub 2/ ambient: a rate equation approach

A new thermal oxidation model based on a rate equation approach with concentration dependent diffusion coefficient is proposed for ultrathin SiO/sub 2/ for thicknesses of the order of 100 /spl Aring/. The oxidation reaction of silicon is assumed to be dependent on the concentrations of unreacted silicon and oxygen. The results of oxide thickness versus oxidation time for various growth conditions and activation energies for diffusion coefficients are in agreement with various experimental data for O/sub 2/ ambient.

Structural stability of WS2 under high pressure

Structural behavior of bulk WS2 under high pressure was investigated using synchrotron X-ray diffraction and diamond anvil cell up to 52 GPa along with high temperature X-ray diffraction and high pressure Raman spectroscopy analysis. The high pressure results obtained from X-ray diffraction and Raman analysis did not show any pressure induced structural phase transformations up to 52 GPa. The high temperature results show that the WS2 crystal structure is stable upon heating up to 600°C. Furthermore, the powder X-ray diffraction obtained on shock subjected WS2 to high pressures up to 10 GPa also did not reveal any structural changes. Our results suggest that even though WS2 is less compressible than the isostructural MoS2, its crystal structure is stable under static and dynamic compressions up to the experimental limit.

Theoretical study of GaN molecular beam epitaxy growth using ammonia: A rate equation approach

III–V nitrides are intensely researched for optoelectronic applications spanning the entire visible spectrum. In spite of realization of commercial devices and advances in processing of materials and devices, the understanding of the processing and epitaxial growth of these materials is incomplete. In this study, a rate equation approach is proposed based on physically sound surface processes to investigate the molecular beam epitaxy growth of GaN using ammonia. A surface riding layer of Ga and ammonia and its associated dynamics such as incorporation of Ga and N in to the crystal and desorption are included in the model. Rates of all surface processes are assumed Arrhenius type. The simulated Ga incorporation rate as a function of ammonia pressure and substrate temperature are in excellent agreement with the experimental data. Ga incorporation increases with increasing NH3 overpressure and saturates at a maximum value at large NH3 overpressure. The Ga incorporation rate exhibits a peak at 820 °C due to c...

The Origin of gallium desorption transients during AlGaAs/GaAs heterointerface formation by molecular beam epitaxy

A Monte Carlo simulation study is performed to investigate the Ga desorption behavior at AlGaAs/GaAs heterointerfaces during growth by molecular beam epitaxy. The transients in Ga desorption rate upon opening/closing the Al shutter arise due to both the change in V/III flux ratio and the Al–Ga surface exchange mechanism. It is shown that the desired “steplike” variation in Ga desorption rate at each interface can be attained by a growth procedure employing a constant V/III flux ratio.

Theoretical study of antisite arsenic incorporation in the low temperature molecular beam epitaxy of gallium arsenide

A stochastic model for simulating the surface growth processes in the low temperature molecular beam epitaxy of gallium arsenide is developed, including the presence and dynamics of a weakly bound physisorbed state for arsenic. The physisorbed arsenic is allowed to incorporate into the arsenic site or gallium site (antisite) and evaporate. Additionally, the antisite As is allowed to evaporate from the surface of the crystal. The arsenic flux, temperature and growth rate dependences of antisite arsenic (AsGa) concentration and the resultant % lattice mismatch obtained from our simulation are in excellent agreement with the experimental results. The activation energy of 1.16 eV for the evaporation of antisite arsenic from the crystal obtained from our model is in good agreement with theoretical estimates. At a constant substrate temperature and growth rate (Ga flux rate), the antisite arsenic concentration and hence, the % lattice mismatch increase with arsenic flux in the low flux regime and saturate for h...

Analysis of Subthreshold Behavior of FinFET using Taurus

This paper investigates the subthreshold behavior of Fin Field Effect Transistor (FinFET). The FinFET is considered to be an alternate MOSFET structure for the deep sub-micron regime, having excellent device characteristics. As the channel length decreases, the study of subthreshold behavior of the device becomes critically important for successful design and implementation of digital circuits. An accurate analysis of subthreshold behavior of FinFET was done by simulating the device in a 3D process and device simulator, Taurus. The subthreshold behavior of FinFET, was measured using a parameter called S-factor which was obtained from the ln(IDS) - VGS characteristics. The value of Sfactor of devices of various fin dimensions with channel length Lg in the range of 20 ㎚ - 50 ㎚ and with the fin width Tfin in the range of 10 ㎚ - 40 ㎚ was calculated. It was observed that for devices with longer channel lengths, the value of S-factor was close to the ideal value of 60 ㎷/dec. The S-factor increases exponentially for channel lengths, Lg < 1.5 Tfin. Further, for a constant Lg, the S factor was observed to increase with Tfin. An empirical relationship between S, Lg and Tfin was developed based on the simulation results, which could be used as a rule of thumb for determining the S-factor of devices.

Modeling and Analysis of the Charging Dynamics in Si-quantum Dots Based Non Volatile Flash Memory Cells

A model including the presence and effect of discrete quantum energy levels and trap states in nanocrystals is proposed in order to describe the anomalous peaks observed in current-voltage characteristics of emerging Si quantum dot based floating gate flash memory cells. The model is employed to investigate the effect of energy levels in quantum dots with a size distribution in the range of 0 to 12 nm in explaining the charging dynamics and current versus time characteristics. The simulated results are in close agreement with the experimental results. It is speculated that the additional peaks observed in the experimental current versus voltage characteristics above threshold voltage are because of the filling up of nanocrystals with more than one electron into quantum levels, shifted to higher energy levels due to the increase in charging energy determined by self capacitance.

Low-temperature molecular beam epitaxy of GaAs: A theoretical investigation of antisite incorporation and reflection high-energy diffraction oscillations

Surface dynamics dominate the incorporation of charged, AsGa+, and neutral, AsGa0, antisite arsenic, and the temporal variation of reflection high-energy electron diffraction (RHEED) intensity in the low-temperature molecular beam epitaxy of (100) gallium arsenide (GaAs). A rate equation model is proposed which includes the presence and dynamics of a physisorbed arsenic (PA) layer riding the growth surface. The PA layer dictates the incorporation and concentration of AsGa+ and AsGa0. Additionally, it influences the RHEED oscillations (ROs) behavior and the RO’s dependence on its coverage through its contribution to the reflected intensity. The model results for the dependence of AsGa+ and AsGa0 concentrations on beam equivalent pressure (BEP) and growth temperature are in good agreement with experimental data. The experimental observations can be explained based on the saturation of the PA coverage at one monolayer and the competing rate processes such as the AsGa incorporation into and evaporation from t...