| 1. |
- Aboelfotoh, M. O., et al.
(författare)
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Schottky-barrier behavior of metals on n- and p-type 6H-SiC
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:7, s. 075312-
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky-barrier height of a number of metals (Ti, Ni, Cu, and Au) on n- and p-type Si-terminated 6H-SiC has been measured in the temperature range 150-500 K. It is found that the barrier height to n-type 6H-SiC does not exhibit a temperature dependence, while for p-type 6H-SiC the change in the barrier height with temperature follows very closely the change in the indirect energy gap in 6H-SiC. These results are inconsistent with models of Schottky-barrier formation based on the concept of a charge neutrality level. Furthermore, the present results cannot be reconciled with a defect pinning mechanism, contrary to the conclusions of earlier studies on III-V compound semiconductors. We suggest that chemical bonding at the metal-semiconductor interface plays an important role in determining the Schottky-barrier height.
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| 2. |
- Achermann, M, et al.
(författare)
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Carrier and field dynamics around nanoscale Schottky contacts investigated by ultrafast near-field optics
- 2002
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 65:4
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Tidskriftsartikel (refereegranskat)abstract
- We present femtosecond-resolved optical near-field pump-probe measurements of spatiotemporal carrier dynamics around a single nanoscale tungsten (W) disk embedded in GaAs. In these samples, Schottky contacts are formed at the W/GaAs interface. The experimental results are modeled by a selfconsistent treatment of the drift-diffusion equation for the carriers and Poisson's equation for the built-in electric field. At lower optically excited carrier densities, we observe that the built-in field suppresses electron transport towards and trapping into the metal particles. In this regime, an accumulation of carriers is seen at the edge of the depletion region of the Schottky contacts. The calculation reveals that the formation of a self-induced dynamic potential well is the origin of this result. In the high-density regime, efficient carrier transport towards and trapping into the W nanoparticle take place, resulting from the screening of the built-in field. These results allow us to describe measurements of the carrier dynamics in annealed low-temperature grown GaAs and demonstrate that the coupling of the carrier and field dynamics can substantially affect carrier trapping in metal-semiconductor composite materials.
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| 3. |
- Adell, M, et al.
(författare)
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Photoemission studies of the annealing-induced modifications of Ga0.95Mn0.05As
- 2004
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 70:12: 125204
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Tidskriftsartikel (refereegranskat)abstract
- Using angle resolved photoemission we have investigated annealing-induced changes in Ga1-xMnxAs with x=0.05. We find that the position of the Fermi energy is a function of annealing time and temperature. It is also established that the Curie temperature is strongly correlated to the separation between the Fermi level and the valence band maximum. Valence band photoemission shows that the Mn3d spectrum is modified by the annealing treatments.
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| 4. |
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| 5. |
- Andersen, O., et al.
(författare)
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Electrical activity of carbon-hydrogen centers in Si
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:23, s. 235205-1
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Tidskriftsartikel (refereegranskat)abstract
- The electrical activity of Cs-H defects in Si has been investigated in a combined modeling and experimental study. High-resolution Laplace capacitance spectroscopy with the uniaxial stress technique has been used to measure the stress-energy tensor and the results are compared with theoretical modeling. At low temperatures, implanted H is trapped as a negative-U center with a donor level in the upper half of the gap. However, at higher temperatures, H migrates closer to the carbon impurity and the donor level falls, crossing the gap. At the same time, an acceptor level is introduced into the upper gap making the defect a positive-U center.
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| 6. |
- Andersson, David A., et al.
(författare)
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Monovacancy and divacancy formation and migration in copper : a first-principles theory
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:11, s. 115108-
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Tidskriftsartikel (refereegranskat)abstract
- The formation and migration of monovacancies and divacancies in copper have been studied from first-principles in order to resolve the discrepancies between previously published experimental and theoretical data. The monovacancy and divacancy formation, migration and binding enthalpies as well as the formation volumes have been calculated in the framework of a plane-wave pseudopotential implementation of the density functional theory, with full structural relaxations included. The monovacancy and divacancy formation entropies have been estimated from experimental data by performing a least-squares analysis. We show that the complete set of first-principles data, taking into account the presence of both vacancies and divacancies as well as the temperature dependence of the formation enthalpies and entropies allow one to reproduce the Arrhenius plot of the total vacancy concentration and the diffusion coefficient, both in good agreement with the most accurate experiments.
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| 7. |
- Andersson, K., et al.
(författare)
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Escape from a zero-current state in a one-dimensional array of Josephson junctions
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:9
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Tidskriftsartikel (refereegranskat)abstract
- A long one-dimensional array of small Josephson junctions exhibits Coulomb blockade of Cooper pair tunneling. This zero-current state exists up to a switching voltage, V-sw, where there is a sudden onset of current. In this paper we present histograms showing how V-sw changes with temperature for a long array and calculations of the corresponding escape rates. Our analysis of the problem is based on the existence of a voltage-dependent energy barrier and we do not make any assumptions about its shape. The data divide into two temperature regimes, the higher of which can be explained with the Kramers thermal escape model. At low temperatures the escape becomes independent of temperature.
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| 8. |
- Andersson, Magnus, et al.
(författare)
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Scaling of the vortex-liquid resistivity in optimally doped and oxygen-deficient YBa2Cu3O7-delta single crystals
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:18, s. 1845111-1845119
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Tidskriftsartikel (refereegranskat)abstract
- The consequences of a recently proposed model [A. Rydh. O. Rapp. and M. Andersson. Phys. Rev. Lett. 83. 1850 (1999)] for the vortex-liquid resistivity close to a vortex liquid-to-glass transition are anal-zed in detail. We find a detailed quantitative agreement between the model and resistivity measurements on disordered, optimally doped YBa2Cu3O7-delta single crystals. For temperatures below the superconducting transition temperature. a scaling of all measured resistivity curves in magnetic field (0
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| 9. |
- Antonyuk, Vadim, et al.
(författare)
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Effect of electron-phonon interaction on electron conductance in one-dimensional systems
- 2004
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 69:15
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the effect of electron-phonon interaction on the electronic transport in a one-dimensional wire where both electrons and phonons are quantum confined. We found substeps appeared in the quantized electron conductance, and the step height depends on the electron-phonon coupling strength. With increasing temperature, the substep structure smooths out. Dependent on the transmission probability through the wire, this substep correction can be either positive or negative. In the limiting cases we reproduce the existing results.
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| 10. |
- Aradi, B., et al.
(författare)
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Ab initio density-functional supercell calculations of hydrogen defects in cubic SiC
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:245202
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Tidskriftsartikel (refereegranskat)abstract
- Based on ab initio density-functional calculations in supercells of 3C-SiC, the stable configurations of hydrogen and dihydrogen defects have been established. The calculated formation energies are used to give semiquantitative estimates for the concentration of hydrogen in SiC after chemical vapor deposition, low temperature H-plasma anneal, or heat treatment in high temperature hydrogen gas. Vibration frequencies, spin distributions, and occupation levels were also calculated in order to facilitate spectroscopic identification of these defects. (V+nH) complexes are suggested as the origin of some of the signals assigned earlier to pure vacancies. Qualitative extrapolation of our results to hexagonal polytypes explains observed electrical passivation effects of hydrogen.
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