| 1. |
- Iwata, H.P., et al.
(author)
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Effective masses of two-dimensional electron gases around cubic inclusions in hexagonal silicon carbide
- 2003
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 0163-1829. ; 68:24, s. 245309-1
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Journal article (peer-reviewed)abstract
- The main purpose of this article is to determine the two-dimensional effective mass tensors of electrons confined in thin 3C wells in hexagonal SiC, which is a first step in the understanding of in-plane electron motion in the novel quantum structures. We have performed ab initio band structure calculations, based on the density functional theory in the local density approximation, for single and multiple stacking faults leading to thin 3C-like regions in 4H- and 6H-SiC and deduced electron effective masses for two-dimensional electron gases around the cubic inclusions. We have found that electrons confined in the thin 3C-like layers have clearly heavier effective masses than in the perfect bulk 3C-SiC single crystal.
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| 2. |
- Iwata, H., et al.
(author)
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A new type of quantum wells : Stacking faults in silicon carbide
- 2003
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In: Microelectronics Journal. - 0026-2692. ; 34:5, s. 371-374
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Conference paper (other academic/artistic)abstract
- We report on a new type of quantum wells with the width as thin as 10Å, which are composed of SiC only, and consequently have ideal interfaces. These quantum wells are actually stacking faults in SiC. Certain types of stacking faults in SiC polytypes create small 3C-like regions, where the stacking sequences along the c-axis become locally cubic in the hexagonal host crystals. Since the conduction band offsets between the cubic and hexagonal polytypes are very large with the conduction band minima of 3C-SiC lower than that of the other polytypes, such thin 3C inclusions can introduce locally lower conduction bands, thus acting as quantum films perpendicular to the c-axis. One mechanism for the occurrence of stacking faults in the perfect SiC single crystals is the motion of partial dislocations in the basal planes, the partial dislocations leaving behind stacking fault regions. © 2003 Elsevier Science Ltd. All rights reserved.
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| 3. |
- Iwata, H., et al.
(author)
-
Cubic polytype inclusions in 4H-SiC
- 2003
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 93:3, s. 1577-1585
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Journal article (peer-reviewed)abstract
- Multiple stacking faults in 4H-SiC, leading to narrow 3C polytype inclusions along the hexagonal c direction, have been studied using an ab initio supercell approach with 96 atoms per supercell. The number of neighboring stacking faults considered is two, three, and four. The wave functions and the two-dimensional energy bands, located in the band gap and associated with the narrow inclusions, can be reconciled with a planar quantum-well model with quantum-well depth equal to the conduction band offset between 3C- and 4H-SiC. We show that the existence of the electronic dipole moment due to the spontaneous polarization leads to a clear asymmetry of the bound wave functions inside the quantum well, and that the perturbation associated with the change in the dipole moment caused by the 3C-like inclusion accounts for the appearance of very shallow localized states at the valence band edge. We have also calculated the stacking fault energies for successive stacking faults. It is found that the stacking fault energy for two stacking faults in adjacent basal planes is reduced by approximately a factor of 4 relative to that of one isolated stacking fault, indicating that double stacking faults in 4H-SiC could be quite common.
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| 4. |
- Iwata, H., et al.
(author)
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Effective mass of electrons in quantum-well-like stacking-fault gap states in silicon carbide
- 2003
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In: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 433-436, s. 519-522
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Journal article (peer-reviewed)abstract
- A first-principles calculation of the effective mass of electrons in quantum-well-like gap states induced by stacking faults and cubic inclusions in 4H- and 6H-SiC is performed, based on the density functional theory in the local density approximation. Our calculated effective electron masses for perfect crystals are in very good agreement with those previously determined both theoretically and experimentally. It has been found that electrons confined in the thin 3C-like regions have clearly heavier effective masses than that in perfect 3C-SiC.
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| 5. |
- Iwata, H, et al.
(author)
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Electronic localization around stacking faults in silicon carbide
- 2002
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In: Materials Science Forum. - Zürich-Uetikon : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-3, s. 529-532, s. 529-532
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Journal article (peer-reviewed)abstract
- First-principles band structure calculations of all the structurally different stacking faults that can be introduced by glide along the (0001) basal plane in 3C-, 4H-, and 6H-SiC are performed, based on the local-density approximation within the density-functional theory. Our calculations, using supercells containing 96 atoms, have revealed that both types of stacking faults in 4H-SiC and two of the three different SFs in 6H-SiC give rise to quasi-2D energy band states in the band gap at around 0.2 eV below the lowest conduction band, and are electrically active. The corresponding wave functions are strongly localized around the stacking fault plane. These results imply that stacking faults in these SiC polytypes are efficient planar traps for electron capture and responsible for subsequent electron-hole recombination. This can therefore have a profound influence on bipolar SiC technology.
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| 6. |
- Iwata, H., et al.
(author)
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Electronic properties of stacking faults in 15R-SiC
- 2003
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In: Silicon carbide and related materials. - Uetikon-Zuerich : Trans Tech Publications Inc.. - 0878499202 ; , s. 531-534
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Conference paper (peer-reviewed)abstract
- A first-principles calculation of stacking faults in 15R-SiC is reported. All the geometrically distinguishable stacking faults which can be introduced by the glide of partial dislocations in (0001)-basal planes are investigated: there exist as many as five different stacking faults in 15R-SiC. Electronic properties and stacking fault energies of these extended defects are studied based on the density functional theory in the local density approximation. Stacking fault energies are also calculated using the axial next nearest neighbor Ising (ANNNI) model.
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| 7. |
- Iwata, H., et al.
(author)
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Electronic structure of twin boundaries in 3C-SiC, Si and diamond
- 2003
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In: Silicon carbide and related materials 2002. - Uetikon-Zuerich : Trans Tech Publications Inc.. - 878499202 ; , s. 527-30
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Conference paper (peer-reviewed)abstract
- We report on a first-principles band structure calculation of twin boundaries in 3C-SiC, Si, and diamond, based on the density functional theory in the local density approximation. It is found that the electron wave functions belonging to the conduction and valence band edge states in 3C-SiC tend to be localized almost exclusively on different sides of the boundaries, while there is no such feature in Si and diamond. We have interpreted these localization and segregation phenomena as a consequence of the electrostatic field caused by the spontaneous polarization due to the hexagonal symmetry around twin boundaries. A mechanism for the creation of twin boundaries, i.e., propagation of partial dislocations in neighboring basal planes, has been investigated using total energy calculations, and it has been realized that the double-intrinsic-stacking-fault structure in 3C-SiC, coinciding with the extrinsic stacking faults, is much energetically favored.
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| 8. |
- Iwata, H.P., et al.
(author)
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Ab initio study of 3 C inclusions and stacking fault-stacking fault interactions in 6H-SiC
- 2003
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94:8, s. 4972-4979
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Journal article (peer-reviewed)abstract
- Ab initio supercell calculations of cubic inclusions in 6H-SiC are performed. The cubic inclusions can be created in perfect 6H-SiC by the propagation of successive partial dislocations having the same Burgers vector in neighboring basal planes, i.e., multiple stacking faults. We have studied the electronic structures and the total energies of 6H-SiC single crystals that contain one, two, three, and four stacking faults, based on density functional theory in local density approximation. Our total energy calculations have revealed that the second stacking fault energy in 6H-SiC is about six to seven times larger than that of an isolated stacking fault, which is actually opposite the trend recently obtained for 4H-SiC [J. Appl. Phys. 93, 1577 (2003)]. The effects of spontaneous polarization on the electronic properties of stacking disorders are examined in detail. The calculated positions of the quantum-well-like localized bands and stacking fault energies of 3C inclusions in 6H-SiC are compared with those previously determined in 4H-SiC, and the possibility of local hexagonal to cubic polytypic transformations is discussed in light of the formation energy and quantum-well action.
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| 9. |
- Iwata, H.P., et al.
(author)
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Energies and electronic properties of isolated and interacting twin boundaries in 3C-SiC, Si, and diamond
- 2003
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 0163-1829. ; 68:11, s. 113202-
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Journal article (peer-reviewed)abstract
- First-principles calculations of twin boundaries in 3C-SiC, Si, and diamond are performed, based on the density-functional theory in the local density approximation. We have investigated the formation energies and electronic properties of isolated and interacting twin boundaries. It is found that in 3C-SiC, interacting twin boundaries which are separated by more than two Si-C bilayers are actually energetically more favorable, implying a relatively frequent appearance of these defects. The effect of the spontaneous polarization associated with the hexagonal symmetry around twin boundaries is also studied, and we have observed that the wave functions belonging to the conduction- and valence-band edge states in 3C-SiC tend to be localized almost exclusively on different sides of the faulted layers, while there is no such feature in Si or diamond.
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| 10. |
- Iwata, H., et al.
(author)
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Stacking fault - stacking fault interactions and cubic inclusions in 6H-SiC : an ab initio study
- 2003
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In: Silicon carbide and related materials. - Uetikon-Zuerich : Trans Tech Publications Inc.. - 0878499202 ; , s. 921-924
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Conference paper (peer-reviewed)abstract
- We report on a first-principles supercell calculation of cubic inclusions in 6H-SiC. Motions of successive partial dislocations having the same Burgers vector in the basal planes can lead to a 3C-like region in the perfect 6H-SiC crystal, which corresponds to multiple stacking faults. We have calculated the electronic structures and the total energies of 6H-SiC crystals containing m stacking faults (m=l-4) in the adjacent basal planes, based on the density functional theory in the local density approximation. It has been found that 3C-like sequences in the 6H-host crystals can act as planar quantum wells, in which conduction band electrons can be confined. The total energy calculations using both the supercell method and the axial next nearest neighbor Ising model (ANNNI) have revealed that the 2nd stacking fault energy in 6H-SiC is about 6 times larger than that of an isolated stacking fault.
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