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THUSHARI Jayasekera - ASSistant Professor

       

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JAYASEKERA-PUBLICATIONS
 

27. Hansika I Sirikumara, Thushari Jayasekera, “Tunable Indirect-Direct Transition of Few-Layer SnSe via Interface Engineering”, Journal of Physics: Condensed Matter, 29, 42, (2017)

26. Hassana Samassekou, Asma Alkabsh, Milinda Wasala, Miller Eaton, Aaron Walber, Andrew Walker, Olli Pitknen, Krisztian Kordas, Saikat Talapatra, Thushari Jayasekera and Dipanjan Mazumdar, “Viable route towards large-area 2D MoS2 using magnetron sputtering”, 2D Materials, 4, 2 (2017).
25. Hansika I. Sirimumara, Thushari Jayasekera, " Buffer-eliminated, charge-neutral epitaxial graphene on oxidized 4H-SiC (0001) surface", Journal of Applied Physics, 119, 215305, (2016).

24. Hansika I. Sirikumara, E. Putz, M. Alabboodi, Thushari Jayasekera, “Symmetry induced semimetal-semiconductor transition in doped graphene”, Scientific Reports, 6, 19115, (2016).

23. Jaime Bohorquez-Ballen, Hansika I. Sirikumara, S. Ahmed, Thushari Jayasekera, “Lattice vibrational properties of Si/Ge core-shell nanowires for thermoelectric applications”, International Workshop on Computational Electronics (IWCE), (2015). DOI: 10.1109/IWCE.2015.7301984

22. M. Z. Rashid, S. Sundaresan, S. Ahmed, Thushari Jayasekera, “VFF-Monte Carlo framework for phonon transport in nanostructures”, International Workshop on Computational Electronics (IWCE), (2015). DOI: 10.1109/IWCE.2015.7301935

21. Hansika I. Sirikumara, Jaime Bohorquez-Ballen, Thushari Jayasekera, "Ge cages at the SiC/graphene interface: A first principles calculation", Journal of Crystal Growth, 393, 145, (2014).



15.  T. Jayasekera, K. W. Kim, M. B. Nardelli, “Electronic properties of turbostratic epitaxial graphene on 6H-SiC surface”, Material Science Forum, 717, 595, (2012).

14. A. Sandin, Thushari Jayasekera, J. Rowe, K. W. Kim, M. B. Nardelli, D. B. Dougherty, “Multiple co-existing intercalation structures of Sodium in epitaxial graphene-SiC interfaces” Phys. Rev. B., 85, 125410, (2012).

13. Thushari Jayasekera, S. Xu, K. W. Kim, M. Buongiorno Nardelli,  “Electronic properties of the  graphene/6H-SiC(000-1) interface, A first principles study”, Phys. Rev. B, 84, 035442 (2011)

12. Y. F. Chen, Thushari Jayasekera, A. Clazolari, K. W. Kim and M. Buongiorno-Nardelli, “Thermoelectric properties of graphene nanoribbons, junctions and superlattices”,  J. Phys. Condens. Matter, Fast Track Communication, 22, 372202, (2010)

11. Thushari Jayasekera, B. D. Kong, K. W. Kim, and M. Buongiorno-Nardelli, “Band Engineering and Magnetic Doping of Epitaxial Graphene on SiC”, Phys. Rev. Lett . 104, 146801 (2010)

10. J. W. Li, Thushari Jayasekera, V. Meunier, and J. W. Mintmire, “Electronic Transport of Silicon Nanowire with Surface Defects”, International Journal of Quantum Chemistry, 109, 3705, (2009)

9. Thushari Jayasekera, B. A. Landis, and J. W. Mintmire, “First-principles simulations of chiral double-wall carbon nanotubes”, International Journal of Quantum Chemistry, 108, 2943, (2008)

8. Thushari Jayasekera, Pavan Pillalamarri, V. Meunier, and J. W. Mintmire, “Effect of phase breaking events on electron transport in mesoscopic and nanoscale devices”, International Journal of Quantum Chemistry, 108, 2896, (2008)

7. Thushari Jayasekera, M. S. Monigold, S. L. Elizondo and J. W. Mintmire,“First principle properties of  organic photovoltaic materials”, International Journal of Quantum Chemistry, 107, 3120 (2007)

6. Thushari Jayasekera, and J. W. Mintmire, “Lattice vacancy effects on electron transport in multi- terminal graphene nanodevices”, International Journal of Quantum Chemistry, 107, 3071 (2007)

5. Thushari Jayasekera, and J.W.Mintmire, “Transport in multi-terminal graphene nanodevices” Nanotechnology, 18, 424033 (2007)

4. Thushari Jayasekera, Kieran Mullen, and Michael A. Morrison, “Cooling electrons in semiconductor devices: A model of evaporative emission”, Phys. Rev. B, 75, 35316 (2007)

3. Thushari Jayasekera, Michael A. Morrison, and Kieran Mullen, “R- matrix theory for magneto- transport properties in semiconductor devices”, Phys. Rev. B, 74, 235308 (2006)

2. Thushari Jayasekera, Niti Goel, Michael A. Morrison, and Kieran Mullen, “Theoretical calculation of  magneto transport properties in semiconductor devices and comparison to experimental data”, Physica E, 34, 584, (2006)

1. Thushari Jayasekera, Michael A. Morrison, and Kieran Mullen, “Evaporative cooling of electrons in semiconductor devices”, AIP Conference Proceedings, 772, 1279, (2004)


27. Tunable Indirect-Direct Transition of Few-Layer SnSe via Interface Engineering

Tin selenide (SnSe) is one of the best thermoelectric materials reported to date. The possibility of growing few-layer SnSe helped boost the interest in this long-known, earth abundant material. Pristine SnSe in bulk, mono- and few-layer forms are reported to have indirect electronic bandgaps. Possible indirect-direct transition in SnSe is attractive for its optoelectronic-related applications. Based on the results from first principles density functional theory calculations, we carefully analyzed electronic band structures of bulk, and bilayer SnSe with various interlayer stackings. We report the possible stacking-dependent indirect-direct transition of bilayer SnSe. By further analysis, our results reveal that it is the directionality of interlayer interactions that determine the critical features of their electronic band structures. In fact, by engineering the interface stacking between layers, it is possible to achieve few-layer SnSe with direct electronic band gap. This study provides fundamental insights to design few-layer SnSe and SnSe heterostructures for electronic/optoelectronic applications, where the interface geometry plays a fundamental role in device performance.
26. Viable route towards large-area 2D MoS2 using magnetron sputtering

Structural, interfacial, optical, and transport properties of large-area MoS2 ultra-thin films on BN-buffered silicon substrates fabricated using magnetron sputtering are investigated. A relatively simple growth strategy is demonstrated here that simultaneously promotes superior interfacial and bulk MoS2 properties. Few layers of MoS2 are established using x-ray reflectivity, diffraction, ellipsometry, and Raman spectroscopy measurements. Layer-specific modeling of optical constants show very good agreement with first-principles calculations. Conductivity measurements reveal that few-layer MoS2 films are more conducting than many-layer films. Photo-conductivity measurements reveal that the sputter deposited MoS2 films compare favorably with other large-area methods. Our work illustrates that sputtering is a viable route for large-area device applications using transition metal dichalcogenides.
2DMaterials



25. Buffer-eliminated, charge-neutral epitaxial graphene on oxidized 4H-SiC (0001) surface
URL
Buffer-eliminated, charge-neutral epitaxial graphene (EG) is important to enhance its potential in device applications. Using the first principles Density Functional Theory calculations, we investigated the effect of oxidation on the electronic and structural properties of EG on 4H-SiC (0001) surface. Our investigation reveals that the buffer layer decouples from the substrate in the presence of both silicate and silicon oxy-nitride at the interface, and the resultant monolayer EG is charge-neutral in both cases. The interface at 4H-SiC/silicate/EG is characterized by surface dangling electrons, which opens up another route for further engineering EG on 4H-SiC. Dangling electron-free 4H-SiC/silicon oxy-nitride/EG is ideal for achieving charge-neutral EG.
 24.  Symmetry induced semimetal-semiconductor transition in doped graphene
URL
Substitutional chemical doping is one way of introducing an electronic bandgap in otherwise semimetallic graphene. A small change in dopant arrangement can convert graphene from a semiconducting to a semimetallic state. Based on ab initio Density Functional Theory calculations, we discuss the electron structure of BN-doped graphene with Bravais and non-Bravais lattice-type defect patterns, identifying semiconducting/semimetallic configurations. Semimetallic behavior of graphene with non-Bravais lattice-type defect patterns can be explained by a phase cancellation in the scattering amplitude. Our investigation reveals for the first time that the symmetry of defect islands and the periodicity of defect modulation limit the phase cancellation which controls the semimetal-semiconductor transition in doped graphene.

23. Lattice vibrational properties of Si/Ge core-shell nanowires for thermoelectric applications
URL

Using first principles Density Functional Theory (DFT) calculations, we have studied the structural and lattice vibrational properties of [111]-oriented Si/Ge core-shell nanowires. Our results show that the fundamental atomicity of the underlying lattice is important for an accurate explanation of phonon frequencies. The detailed analysis shows that thermal conductance due to selective phonon modes of Si/Ge coreshell nanowires can be suppressed by engineering the ratio of core/shell atoms, as well as the detailed atomistic configuration. In particular, our results reveal that heavier shell atoms in Si/Ge core-shell nanowires reduce thermal conductivity, increasing their thermoelectric figure of merit.
22. VFF-Monte Carlo framework for phonon transport in nanostructures
URL
Accurate modeling of non-equilibrium heat  transport in nanostructures demands an appropriate description of phonon dispersion relation and proper treatment of various anharmonic effects. In this work, we develop and employ a coupled VFF molecular mechanics Monte Carlo (VFF-MC) platform to solve the pho non Boltzmann Transport Equation (BTE) for modeling thermal conductivity in nanostructures having specified geometry

21. Ge cages at the SiC/graphene interface: A first principles calculation
Journal of Crystal Growth, 393, 145, (2014). URL

Using the first principles density functional theory calculations, we investigated the effect of Ge atoms on the electronic and structural properties of epitaxial graphene on the Si-face of SiC. We considered both the substituted Ge atoms and intercalated multilayers of Ge at the interface. Starting with Ge3 clusters, we introduce one to six monolayers (ML) of Ge at the interface. Our first-principles density functional theory (DFT) calculations find that, when there are more than four ML, the periodicity of the most stable atomistic configuration of Ge atoms in between the buffer layer and the SiC substrate is influenced by the periodicity of the substrate underneath, as well as the periodicity of the honeycomb array of C atoms on the top. Two distinct Ge cages are formed which are merged in to each other. As a result of the intercalation, the buffer layer decouples from the substrate converting it to graphene. Within the scope of our calculations, we found electron-doped graphene with Ge intercalation.

20. Tunable Electronics in Large-Area Atomic Layers of Boron-Nitrogen-Carbon
Nano Letters, 13, 3476, (2013) URL

We report on the low-temperature electrical transport properties of large area boron and nitrogen codoped graphene layers (BNC). The temperature dependence of resistivity (5 K < T < 400 K) of BNC layers show semiconducting nature and display a band gap which increases with B and N content, in sharp contrast to large area graphene layers, which shows metallic behavior. Our investigations show that the amount of B dominates the semiconducting nature of the BNC layers. This experimental observations agree with the density functional theory (DFT) calculations performed on BNC structures similar in composition to the experimentally measured samples. In addition, the temperature dependence of the electrical conductivity of these samples displays two regimes: at higher temperatures, the doped samples display an Arrhenius-like temperature dependence thus indicating a well-defined band gap. At the lowest temperatures, the temperature dependence of the conductivity deviates from activated behavior and displays a conduction mechanism consistent with Mott’s two-dimensional (2D) variable range hopping (2D-VRH). The ability to tune the electronic properties of thin layers of BNC by simply varying the concentration of B and N will provide a tremendous boost for obtaining materials with tunable electronic properties relevant to applications in solid state electronics.
19.  First-principles calculation of thermal transport in metal/graphene systems
Phys. Rev. B., 87, 165410, (2013) URL

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Thermal properties in the metal/graphene (Gr) systems are analyzed by using an atomistic phonon transport model based on Landauer formalism and first-principles calculations. The specific structures under investigation include chemisorbed Ni(111)/Gr, physisorbed Cu(111)/Gr and Au(111)/Gr, as well as Pd(111)/Gr with intermediate characteristics. Calculated results illustrate a strong dependence of thermal transfer on the details of interfacial microstructures. In particular, it is shown that the chemisorbed case provides a generally smaller interfacial thermal resistance than the physisorbed one due to the stronger bonding. However, our calculation also indicates that the weakly chemisorbed interface of Pd/Gr may be an exception, with the largest thermal resistance among the considered. Further examination of the electrostatic potential and interatomic force constants reveals that the mixed bonding force between the Pd and C atoms results in incomplete hybridization of Pd and graphene orbital states at the junction, leading effectively to two phonon interfaces and a larger than expected thermal resistance. Comparison with available experimental data shows good agreement. The result clearly suggests the feasibility of phonon engineering for thermal property optimization at the interface.

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18. Ab initio thermal transport properties of nanostructures from density functional perturbation theory
J. Phys: Condens. Matter, 24, 492204, (2012) URL
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We present a comprehensive first-principles study of the thermal transport properties of low-dimensional nanostructures such as polymers and nanowires. An approach is introduced where the phonon quantum conductance is computed from the combination of accurate plane-wave density functional theory electronic structure calculations, the evaluation of the interatomic force constants through density functional perturbation theory for lattice dynamics, and the calculation of transport properties by a real-space Green's function method based on the Landauer formalism. This approach is computationally very efficient, can be straightforwardly implemented as a post-processing step in a standard electronic structure calculation (Quantum ESPRESSO and WanT in the present implementation), and allows us to directly link the thermal transport properties of a device to the coupling, dimensionality, and atomistic structure of the system. It provides invaluable insight into the mechanisms that govern heat flow at the nanoscale and paves the way to the fundamental understanding of phonon engineering in nanostructures.

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17. Phonon engineering in  nanostructures: Controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions 
App. Phys. Lett., 101, 113111, (2012)  URL
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Using calculations from first principles and the Landauer approach for phonon transport, we study the Kapitza resistance in selected multilayer graphene/dielectric heterojunctions (hexagonal BN and wurtzite SiC) and demonstrate (i) the resistance variability ( ∼ 50−700×10−10 m2K/W) induced by vertical coupling, dimensionality, and atomistic structure of the system and (ii) the ability of understanding the intensity of the thermal transmittance in terms of the phonon distribution at the interface. Our results pave the way to the fundamental understanding of active phonon engineering by microscopic geometry design.


16. Charge transfer equilibria in ambient-exposed epitaxial grapheme on (000-1) 6H-SiC
Jou. of App. Phys. 11,113706, (2012) URL
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The transport properties of electronic materials have been long interpreted independently from both the underlying bulk-like behavior of the substrate or the influence of ambient gases. This is no longer the case for ultra-thin graphene whose properties are dominated by the interfaces between the active material and its surroundings. Here, we show that the graphene interactions with its environments are critical for the electrostatic and electrochemical equilibrium of the active device layers and their transport properties. Based on the prototypical case of epitaxial graphene on (000) 6 H-SiC and using a combination of in-situ thermoelectric power and resistance measurements and simulations from first principles, we demonstrate that the cooperative occurrence of an electrochemically mediated charge transfer from the graphene to air, combined with the peculiar electronic structure of the graphene/SiC interface, explains the wide variation of measured conductivity and charge carrier type found in prior reports.
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15. Electronic properties of turbostratic epitaxial graphene on 6H-SiC surface
Material Science Forum, 717, 595, (2012)

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We propose an atomistic model to study the interface properties of mis-oriented (Wrbostratic) epitaxial graphene on the 6H-SiC (000-1) surface. Using calculations from first principles, we compare the energetics and structural/electronic properties of AB and turbostratic stacking sequences within a model based on the Si adatom surface reconstruction. Our calculations show that the systems with AB and turbostratic sequences are very close in energy, demonstrating the possibility of observation of Moire patterns in epitaxial graphene on the C-face of 6H-SiC. The two-dimensional electron gas behavior is preserved in the epitaxial turbostratic graphene systems. However, there are deviations from the ideal turbostratic graphene.
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14. Multiple co-existing intercalation structures of Sodium in epitaxial graphene-SiC interfaces
Phys. Rev. B., 85,  125410, (2012) URL
14_exp        14_Theory
We show using scanning tunneling microscopy, spectroscopy, and ab initio calculations that two intercalation structures coexist for Na in epitaxial graphene on SiC(0001). Intercalation takes place at room temperature, and Na electron dopes the graphene. It inserts in between single-layer graphene and the interfacial layer and also penetrates beneath the interfacial layer and decouples it to form a second graphene layer. Decoupling is accelerated by annealing and is verified by Na deposition onto the interface layer combined with computational modeling of the two new decoupled buffer layer structures.

13. Electronic properties of the graphene/6H-SiC(000-1) interface, A first principles study
Phys. Rev. B, 84, 035442 (2011) URL

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Using calculations from first principles, we show how the structural and electronic properties of epitaxial graphene on 6H-SiC(0001̅ ) are determined by the geometry and the chemical functionalization of the interface region. We also demonstrate that these properties can be correctly captured only if a proper treatment of the van der Waals interactions is included in the theoretical description based on density functional theory. Our results reproduce the experimentally observed n-type doping of monolayer epitaxial graphene and prove the possibility of opening a sizable (150 meV) energy gap in the bilayer case under special growth conditions. Depending on the details of the bonding at the interface, we are able to interpret recent experimental observations and provide a clear insight into the mechanisms of charge transfer and interface stability.

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12. Thermoelectric properties of graphene nanoribbons, junctions and superlattices
J. Phys. Condens. Matter, Fast Track Communication, 22, 372202, (2010) URL

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Using model interaction Hamiltonians for both electrons and phonons and Green's function formalism for ballistic transport, we have studied the thermal conductance and the thermoelectric properties of graphene nanoribbons (GNR), GNR junctions and periodic superlattices. Among our findings we have established the role that interfaces play in determining the thermoelectric response of GNR systems both across single junctions and in periodic superlattices. In general, increasing the number of interfaces in a single GNR system increases the peak ZT values that are thus maximized in a periodic superlattice. Moreover, we proved that the thermoelectric behavior is largely controlled by the width of the narrower component of the junction. Finally, we have demonstrated that chevron-type GNRs recently synthesized should display superior thermoelectric properties.

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11. Band Engineering and Magnetic Doping of Epitaxial Graphene on SiC
Phys. Rev. Lett . 104, 146801 (2010) URL

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Using calculations from first principles we show how specific interface modifications can lead to a fine-tuning of the doping and band alignment in epitaxial graphene on SiC. Upon different choices of dopants, we demonstrate that one can achieve a variation of the valence band offset between the graphene Dirac point and the valence band edge of SiC up to 1.5 eV. Finally, via appropriate magnetic doping one can induce a half-metallic behavior in the first graphene monolayer. These results clearly establish the potential for graphene utilization in innovative electronic and spintronic devices.
10. Electronic Transport of Silicon Nanowire with Surface Defects
International Journal of Quantum Chemistry, 109, 3705, (2009) URL

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We report first-principle results for the electronic transport properties of silicon nanowires along the 〈110〉 direction with hydroxyl surface defects. The Hamiltonian and overlap matrices of the system are obtained using an all-electron, Gaussian-basis, local-density functional approach adapted for helical symmetry and the transport calculation makes use of the Landauer approach. We show that the hydroxyl defects can greatly reduce the conductance of hydrogen-passivated Si nanowires and can be used to tune the conductance of the silicon nanowires.

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9. First-principles simulations of chiral double-wall carbon nanotubes
International Journal of Quantum Chemistry, 108, 2943, (2008) URL
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We discuss the use of helical symmetry to carry out first-principles band structure calculations of double-wall carbon nanotubes (DWNTs). While several first-principles calculations have been carried out for double-wall armchair nanotubes using translational symmetry since the early work by Charlier and Michenaud in 1993, few calculations have been carried out for double-wall carbon nanotubes containing chiral single-wall nanotubes. The use of helical symmetry reduces the size of the unit cell, and consequently reduces the computational difficulty of calculating the electronic structure of chiral DWNTs. Calculations carried out for a range of interlayer separations show a minimum cohesive energy around 0.35 nm as expected from experimental results.
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8. Effect of phase breaking events on electron transport in mesoscopic and nanoscale devices
International Journal of Quantum Chemistry, 108, 2896, (2008) URL
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Existing ballistic models for electron transport in mesoscopic and nanoscale systems break down as the size of the device becomes longer than the phase coherence length of electrons in the system. Krstic et al. experimentally observed that the current in single-wall carbon nanotube systems can be regarded as a combination of a coherent part and a noncoherent part. In this article, we discuss the use of Büttiker phase-breaking technique to address partially coherent electron transport, generalize that to a multichannel problem, and then study the effect of phase-breaking events on the electron transport in two-terminal graphene nanoribbon devices. We also investigate the difference between the pure-phase randomization and phase/momentum randomization boundary conditions. While momentum randomization adds an extra resistance caused by backward scattering, pure-phase randomization smooths the conductance oscillations because of interference.
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7. First principle properties of organic photovoltaic materials
International Journal of Quantum Chemistry, 107, 3120 (2007) URL

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One major approach for efficient photovoltaic devices based on polymeric materials lies in the use of bulk heterojunctions, which mix two different organic polymeric materials acting as donor and acceptor semiconductors. In these bulk heterojunctions the donor polymer typically acts as the light absorber, creating an electron-hole pair and then donating the excited electron to the acceptor polymer. A deep theoretical understanding of the physical processes at work in these materials will require a knowledge of the electron states near the Fermi level for both the donor and acceptor. Bulk heterojunction systems based on mixtures of single-wall carbon nanotubes and poly(3-octylthiophene) have recently been reported in the literature. We calculate the electronic structure for both semiconducting and metallic single-wall nanotubes, and compare these with electronic structure results for poly(3-methylthiophene) as a model for the poly(3-alkyl-thiophenes). We also present results for the effective mass of single-wall carbon nanotubes and poly(3-methyl-thiophene) using the calculated electronic band structures.

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6. Lattice vacancy effects on electron transport in multi-terminal graphene nanodevices
Nanotechnology, 18, 424033 (2007) URL

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We investigate the effect of single lattice vacancies on the electron transport of graphene nanoribbon devices using the Landauer formalism within a tight binding approach. For a zigzag nanoribbon, a single lattice vacancy creates conductance dips in the low energy region, due to quasi bound states around the vacancy site. The energy of the bound state is related to the position of the lattice vacancy relative to the edge of the ribbon. We carried out calculations of electron transport properties in a T-junction device with lattice vacancies. We find that the effect of the vacancies depends on how energetically favorable the lattice vacancy is, which can be studied in terms of the alternate atomic structure of the graphene lattice.

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5. Transport in multi-terminal graphene nanodevices                   
  Nanotechnology, 18, 424033 (2007) URL
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We study the transport properties of multiterminal graphene nanodevices using the Landauer-Buttiker approach and the tight binding model. We consider a four-terminal device made at the crossing of a zigzag and armchair nanoribbons and two types of T-junction devices. The transport properties of graphene multiterminal devices are highly sensitive to the details of the junction region. Thus the properties are drastically different from those on the armchair and zigzag counterparts. In the cross-junction device, we see a conductance dip in the armchair lead associated with a conductance peak in the zigzag lead. We find that this effect is enhanced in a T-junction device with one armchair sidearm.

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4. Cooling electrons in semiconductor devices: A model of evaporative emission
Phys. Rev. B, 75, 35316 (2007) URL
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We discuss the theory of cooling electrons in solid-state devices via “evaporative emission.” Our model is based on filtering electron subbands in a quantum-wire device. When incident electrons in a higher-energy subband scatter out of the initial electron distribution, the system equilibrates to a different chemical potential and temperature than those of the incident electron distribution. We show that this re-equilibration can cause considerable cooling of the system. We discuss how the device geometry affects the final electron temperatures, and consider factors relevant to possible experiments. We demonstrate that one can therefore induce substantial electron cooling due to quantum effects in a room-temperature device. The resulting cooled electron population could be used for photodetection of optical frequencies corresponding to thermal energies near room temperature.

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3. R- matrix theory for magneto-transport properties in semiconductor devices
Phys. Rev. B, 74, 235308 (2006) URL

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Many problems in nano and molecular electronics require the solution of the Schrodinger equation for scattering states. R-matrix theory, a technique first introduced in nuclear physics and widely used in atomic and molecular physics, has recently been adapted to calculate the transport properties of solid-state devices. We have extended R-matrix theory to the general case of two-dimensional devices in the presence of an external perpendicular magnetic field. We apply this technique to a particular device and calculate the magnetotransport properties of a two-dimensional “cross” junction.

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2. Theoretical calculation of     magneto transport properties in semiconductor devices and comparison to experimental data
Physica E, 34, 584, (2006) URL
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Negative bend resistance is a signature of ballistic transport in low-dimension semiconductor devices. We calculate the bend resistance in 4-terminal devices using R-matrix theory. R-matrix theory is a technique first introduced in nuclear physics and recently shown to be a useful tool for calculating transport properties of solid-state devices. We have improved upon the existing implementations of R-matrix theory in device physics by applying a variational basis function approach that dramatically improves the rate of convergence of transmission coefficients. We have also developed a method for calculating transmission coefficients of a device in a nonzero magnetic field. We calculate bend resistance in 4-terminal devices.

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1. Evaporative cooling of electrons in semiconductor devices
AIP Conference Proceedings, 772, 1279, (2004)

We discuss the theory of cooling of electrons in solid-state devices by evaporative emission. Our model is based on filtering electron subbands in a quantum-wire device. When the higher-subband electrons scatter out of the initial electron distribution, the system equilibrates at a different chemical potential and temperature than those of the input system. Our calculation shows that such filtering can give considerable cooling. We discuss the effect of device geometry on cooling.
Thushari Jayasekera, Assistant Professor of Physics, Southern Illinois University - Carbondale
Tel: 618 453 1055 Fax: 618 453 1056

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