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Papers by neophytos neophytou
IEEE Transactions on Nanotechnology, 2006
IEEE Transactions on Electron Devices, 2007
Nano Letters, 2008
The effects of the various contact types and shapes on the performance of Schottky barrier graphe... more The effects of the various contact types and shapes on the performance of Schottky barrier graphene nanoribbon field-effect-transistors (GNRFETs) have been investigated using a real-space quantum transport simulator based on the NEGF approach self-consistently coupled to a three-dimensional Poisson solver for treating the electrostatics. The device channel considered is a double gate semiconducting armchair nanoribbon. The types of contacts considered are (a) a semi-infinite normal metal, (b) a semi-infinite graphene sheet, (c) finite size rectangular shape armchair graphene contacts, (d) finite size wedge shape graphene contacts, and (e) zigzag graphene nanoribbon contacts. Among these different contact types, the semi-infinite graphene sheet contacts show the worst performance because of their very low density of states around the Dirac point resulting in low transmission possibility through the Schottky barrier, both at ON and OFF states. Although all other types of contacts can have significant enhancement in I ON to I OFF ratio, the zigzag GNR contacts show promising and size invariant performance due to the metallic properties.
International Journal of High Speed Electronics and Systems, 2006
A realistic 40 nm InAs high electron mobility transistor is studied using a two-dimensional, full... more A realistic 40 nm InAs high electron mobility transistor is studied using a two-dimensional, full-band, and atomistic Schrodinger-Poisson solver based on the sp 3 d 5 s*. tight-binding model. Bandstructure non-parabolicity effects, strain, alloy disorder in the InGaAs and InAlAs barriers, as well as band-to-band tunneling in the transistor OFF-state are automatically included through the full-band atomistic model. The source and drain contact extensions are taken into account a posteriori by adding two series resistances to the device channel. The simulated current characteristics are compared to measured data and show a good quantitative agreement.
Journal of Computational Electronics, 2008
The ballistic performance of graphene nanoribbon (GNR) MOSFETs with different width of armchair G... more The ballistic performance of graphene nanoribbon (GNR) MOSFETs with different width of armchair GNRs is examined using a real-space quantum simulator based on the Non-equilibrium Green’s Function (NEGF) approach, self-consistently coupled to a 3D Poisson’s equation for electrostatics. GNR MOSFETs show promising device performance, in terms of low subthreshold swing and small drain-induced-barrier-lowing due to their excellent electrostatics and gate control (single monolayer). However, the quantum tunneling effects play an import role in the GNR device performance degradation for wider width GNR MOSFETs due to their reduced bandgap. At 2.2 nm width, the OFF current performance is completely dominated by tunneling currents, making the OFF-state of the device difficult to control.
IEEE Transactions on Nanotechnology, 2006
![Research paper thumbnail of Design Space for Low Sensitivity to Size Variations in [110] PMOS Nanowire Devices: The Implications of Anisotropy in the Quantization Mass](https://attachments.academia-assets.com/36195727/thumbnails/1.jpg)
](A 20-band sp3d5s* spin-orbit-coupled, semi-empirical, atomistic tight-binding model is used with ... more A 20-band sp3d5s* spin-orbit-coupled, semi-empirical, atomistic tight-binding model is used with a semi-classical, ballistic, field-effect-transistor (FET) model, to examine the ON-current variations to size variations of [110] oriented PMOS nanowire devices. Infinitely long, uniform, rectangular nanowires of side dimensions from 3nm to 12nm are examined and significantly different behavior in width vs. height variations are identified and explained. Design regions are identified, which show minor ON-current variations to significant width variations that might occur due to lack of line width control. Regions which show large ON-current variations to small height variations are also identified. The considerations of the full band model here show that ON-current doubling can be observed in the ON-state at the onset of volume inversion to surface inversion transport caused by structural side size variations. Strain engineering can smooth out or tune such sensitivities to size variations. The cause of variations described is the structural quantization behavior of the nanowires, which provide an additional variation mechanism to any other ON-current variations such as surface roughness, phonon scattering etc.
Journal of Computational Electronics, 2008
The ballistic performance of electron transport in nanowire transistors is examined using a 10 or... more The ballistic performance of electron transport in nanowire transistors is examined using a 10 orbital sp3d5s* atomistic tight-binding model for the description of the electronic structure, and the top-of-the-barrier semiclassical ballistic model for calculation of the transport properties of the transistors. The dispersion is self consistently computed with a 2D Poisson solution for the electrostatic potential in the cross section of the wire. The effective mass of the nanowire changes significantly from the bulk value under strong quantization, and effects such as valley splitting strongly lift the degeneracies of the valleys. These effects are pronounced even further under filling of the lattice with charge. The effective mass approximation is in good agreement with the tight binding model in terms of current–voltage characteristics only in certain cases. In general, for small diameter wires, the effective mass approximation fails.
IEEE Transactions on Electron Devices, 2009
One of the most expensive operations in volume rendering is the interpolation of samples in volum... more One of the most expensive operations in volume rendering is the interpolation of samples in volume space. The number of samples, in turn, depends on the resolution of the final image. Hence, viewing the volume at high magnification will incur heavy computation. In this paper, we explore an approach that limits the number of samples to the resolution of the
This paper discusses how to squeeze volume rendering into as few bits per operation as possible w... more This paper discusses how to squeeze volume rendering into as few bits per operation as possible while still retaining excellent image quality. For each of the typical volume rendering pipeline stages in texture map volume rendering, ray casting and splatting we provide a quantitative analysis of the theoretical and practical limits for the required bit precision for computation and storage. Applying this analysis to any volume rendering implementation can balance the internal precisions based on the desired final output precision and can result in significant speedups and reduced memory footprint.
IEEE Transactions on Nanotechnology, 2006
IEEE Transactions on Electron Devices, 2007
Nano Letters, 2008
The effects of the various contact types and shapes on the performance of Schottky barrier graphe... more The effects of the various contact types and shapes on the performance of Schottky barrier graphene nanoribbon field-effect-transistors (GNRFETs) have been investigated using a real-space quantum transport simulator based on the NEGF approach self-consistently coupled to a three-dimensional Poisson solver for treating the electrostatics. The device channel considered is a double gate semiconducting armchair nanoribbon. The types of contacts considered are (a) a semi-infinite normal metal, (b) a semi-infinite graphene sheet, (c) finite size rectangular shape armchair graphene contacts, (d) finite size wedge shape graphene contacts, and (e) zigzag graphene nanoribbon contacts. Among these different contact types, the semi-infinite graphene sheet contacts show the worst performance because of their very low density of states around the Dirac point resulting in low transmission possibility through the Schottky barrier, both at ON and OFF states. Although all other types of contacts can have significant enhancement in I ON to I OFF ratio, the zigzag GNR contacts show promising and size invariant performance due to the metallic properties.
International Journal of High Speed Electronics and Systems, 2006
A realistic 40 nm InAs high electron mobility transistor is studied using a two-dimensional, full... more A realistic 40 nm InAs high electron mobility transistor is studied using a two-dimensional, full-band, and atomistic Schrodinger-Poisson solver based on the sp 3 d 5 s*. tight-binding model. Bandstructure non-parabolicity effects, strain, alloy disorder in the InGaAs and InAlAs barriers, as well as band-to-band tunneling in the transistor OFF-state are automatically included through the full-band atomistic model. The source and drain contact extensions are taken into account a posteriori by adding two series resistances to the device channel. The simulated current characteristics are compared to measured data and show a good quantitative agreement.
Journal of Computational Electronics, 2008
The ballistic performance of graphene nanoribbon (GNR) MOSFETs with different width of armchair G... more The ballistic performance of graphene nanoribbon (GNR) MOSFETs with different width of armchair GNRs is examined using a real-space quantum simulator based on the Non-equilibrium Green’s Function (NEGF) approach, self-consistently coupled to a 3D Poisson’s equation for electrostatics. GNR MOSFETs show promising device performance, in terms of low subthreshold swing and small drain-induced-barrier-lowing due to their excellent electrostatics and gate control (single monolayer). However, the quantum tunneling effects play an import role in the GNR device performance degradation for wider width GNR MOSFETs due to their reduced bandgap. At 2.2 nm width, the OFF current performance is completely dominated by tunneling currents, making the OFF-state of the device difficult to control.
IEEE Transactions on Nanotechnology, 2006
A 20-band sp3d5s* spin-orbit-coupled, semi-empirical, atomistic tight-binding model is used with ... more A 20-band sp3d5s* spin-orbit-coupled, semi-empirical, atomistic tight-binding model is used with a semi-classical, ballistic, field-effect-transistor (FET) model, to examine the ON-current variations to size variations of [110] oriented PMOS nanowire devices. Infinitely long, uniform, rectangular nanowires of side dimensions from 3nm to 12nm are examined and significantly different behavior in width vs. height variations are identified and explained. Design regions are identified, which show minor ON-current variations to significant width variations that might occur due to lack of line width control. Regions which show large ON-current variations to small height variations are also identified. The considerations of the full band model here show that ON-current doubling can be observed in the ON-state at the onset of volume inversion to surface inversion transport caused by structural side size variations. Strain engineering can smooth out or tune such sensitivities to size variations. The cause of variations described is the structural quantization behavior of the nanowires, which provide an additional variation mechanism to any other ON-current variations such as surface roughness, phonon scattering etc.
Journal of Computational Electronics, 2008
The ballistic performance of electron transport in nanowire transistors is examined using a 10 or... more The ballistic performance of electron transport in nanowire transistors is examined using a 10 orbital sp3d5s* atomistic tight-binding model for the description of the electronic structure, and the top-of-the-barrier semiclassical ballistic model for calculation of the transport properties of the transistors. The dispersion is self consistently computed with a 2D Poisson solution for the electrostatic potential in the cross section of the wire. The effective mass of the nanowire changes significantly from the bulk value under strong quantization, and effects such as valley splitting strongly lift the degeneracies of the valleys. These effects are pronounced even further under filling of the lattice with charge. The effective mass approximation is in good agreement with the tight binding model in terms of current–voltage characteristics only in certain cases. In general, for small diameter wires, the effective mass approximation fails.
IEEE Transactions on Electron Devices, 2009
One of the most expensive operations in volume rendering is the interpolation of samples in volum... more One of the most expensive operations in volume rendering is the interpolation of samples in volume space. The number of samples, in turn, depends on the resolution of the final image. Hence, viewing the volume at high magnification will incur heavy computation. In this paper, we explore an approach that limits the number of samples to the resolution of the
This paper discusses how to squeeze volume rendering into as few bits per operation as possible w... more This paper discusses how to squeeze volume rendering into as few bits per operation as possible while still retaining excellent image quality. For each of the typical volume rendering pipeline stages in texture map volume rendering, ray casting and splatting we provide a quantitative analysis of the theoretical and practical limits for the required bit precision for computation and storage. Applying this analysis to any volume rendering implementation can balance the internal precisions based on the desired final output precision and can result in significant speedups and reduced memory footprint.