| 1. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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A complex defect related to the carbon vacancy in 4H and 6H SiC
- 1999
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T79, s. 46-49
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Tidskriftsartikel (refereegranskat)abstract
- Electron paramagnetic resonance (EPR) was used to study defects in 4H and 6H SiC irradiated with 2.5 MeV electrons at room temperature. When the dose of irradiation reaches ~ 5 × 1017 electrons/cm2, an EPR spectrum appears. In both 4H and 6H SiC, the defect associated with this spectrum has C1h symmetry with an effective electron spin S = 1 and an isotropic g-value of 2.0063 ± 0.0002. The crystal-field parameter was determined as D = 1.65 and D = 1.67 GHz for 4H and 6H SiC, respectively. The principal crystal-field axis lies in the (11bar 20) plane and makes an angle of ~ 46° with the c-axis for both polytypes. A clear hyperfine structure from 29Si due to the interaction with four nearest silicon neighbours was observed, confirming that the defect is related to the carbon vacancy. The similarity in all respects including the annealing behaviour of the spectrum in both polytypes suggests that it belongs to the same defect. Based on the formation and its electronic structure, the defect is suggested to be a complex with one of the components being the carbon vacancy.
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| 2. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Carbon-vacancy related defects in 4H- and 6H-SiC
- 1999
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Ingår i: Materials Science and Engineering B, Vol. 61-62. - : Elsevier. ; , s. 202-
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Konferensbidrag (refereegranskat)abstract
- Electron paramagnetic resonance (EPR) was used to study intrinsic defects in 4H- and 6H-SiC irradiated with 2.5 MeV electrons with doses ranging from 1×1017 to 2×1018 cm−2. In p-type 4H- and 6H-SiC, the dominant EPR signal, labeled EI1, associates with a defect centre having a low symmetry and an effective electron spin S=1/2. For both polytypes, its g-tensor was determined as gz=2.0015, gx=1.9962 and gy=2.0019, where gz and gx lie in the (11Image 0) plane and the z-axis makes an angle not, vert, similar41 degrees with the c-axis. Hyperfine interaction with a 29Si atom located at two equivalent sites in the nearest neighbour shell was detected, confirming that the defect resides at the carbon site. In heavily irradiated 4H- and 6H-SiC, a new EPR spectrum having an electron spin S=1, labeled EI3, was observed. In both polytypes, the EI3 centre has a low symmetry, an isotropic g-value of 2.0063 and a fine structure parameter |D|not, vert, similar5.5×10−2 cm−1. The observed hyperfine interaction with four 29Si atoms in the nearest neighbour shell confirms the involvement of the carbon vacancy in the defect. The defect is suggested to be a complex centre involving a carbon vacancy.
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| 3. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Electron-paramagnetic-resonance studies of defects in electron-irradiated p-type 4H and 6H SiC
- 1999
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 655-658
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Tidskriftsartikel (refereegranskat)abstract
- Defects in p-type 4H and 6H SiC irradiated by 2.5 MeV electrons were studied by electron paramagnetic resonance (EPR). Two anisotropic EPR spectra, labeled I and II, were observed in both 4H and 6H SiC. These spectra demonstrating triclinic symmetry of the center can be described by an effective electron spin S=1/2. The angle α between the direction of the principal gz of the g-tensors and the c-axis is determined as 63° and 50° for spectra I and II, respectively. In the 6H polytype, a third also similar EPR spectrum was detected. Based on their similarity in the electronic structure (electron spin, symmetry, g values), annealing behavior and temperature dependence, these spectra are suggested to be related to the same defect occupying different inequivalent lattice sites in 4H and 6H SiC. A pair between a silicon vacancy and an interstitial is a possible model for the defect.
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| 4. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Optically detected magnetic resonance studies of intrinsic defects in 6H-SiC
- 1999
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Ingår i: Semiconductor Science and Technology. - 0268-1242 .- 1361-6641. ; 14:12, s. 1141-1146
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Tidskriftsartikel (refereegranskat)abstract
- Optically detected magnetic resonance (ODMR) was used for study of defects in n-type 6H-SiC. Four ODMR spectra related to spin S = 1 centres were observed. Two of these centres, labelled a and b, have a trigonal symmetry with the symmetry axis along the c-axis of the hexagonal crystal. For the other two centres, labelled c and d, the symmetry is lower (C1h) and the principal axis z of the g- and D-tensor is about 71 degrees off the c-axis. Based on the symmetry axes, the annealing behaviour and the intensity, these spectra are suggested to originate from different configurations of the paired centre between a silicon vacancy and a nearest-neighbour point defect (either a carbon vacancy or a silicon antisite), occupying different inequivalent sites in the 6H-SiC. These defects are non-radiative and act as efficient recombination channels in the material.
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| 5. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Photoluminescence and Zeeman effect in chromium-doped 4H and 6H SiC
- 1999
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 86:8, s. 4348-
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Tidskriftsartikel (refereegranskat)abstract
- Photoluminescence (PL) and Zeeman effect measurements in near-infrared luminescence bands in Cr-doped 4H and 6H SiC are presented. The PL spectrum consists of two no-phonon lines (NPLs) at 1.1583 and 1.1898 eV in 4H SiC and three NPLs at 1.1556, 1.1797, and 1.1886 eV in 6H SiC. The observed Zeeman splittings and temperature dependence studies reveal the spin triplet of the ground state and the orbital doublet structure of the excited state of the Cr-related center. All the triplets have almost isotropic g values close to 2 with trigonal symmetry and small zero-field splitting values D. In contrast, the effective g values of the excited state of the center are very anisotropic with g|| in the range of 0.22-0.64 and g[perpendicular] = 0 for different NPLs in both polytypes. Based on the Zeeman results, the PL is attributed to the internal transition 1E(D)-->3A2(F) within the d shell of a substitutional, neutral chromium (Cr4 + ) in the 3d2 electronic configuration.
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| 6. |
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| 7. |
- Wagner, Matthias, 1969-, et al.
(författare)
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Zeeman spectroscopy of the neutral silicon vacancy in 6H and 4H SiC
- 1999
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Ingår i: Physica B. Vol. 273-274. - : Elsevier. ; , s. 663-
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Konferensbidrag (refereegranskat)abstract
- High-resolution photoluminescence (PL) and PL excitation (PLE) spectroscopy has been employed to reveal the electronic structure of the neutral silicon vacancy in 6H and 4H SiC. The defect gives rise to characteristic PL emissions with three no-phonon lines in 6H SiC and two in 4H SiC at around 1.4 eV. All of the no-phonon lines are shown to arise from transitions between singlet (S=0) excited states and singlet ground states. Nevertheless, optically detected magnetic resonance (ODMR) signals typical for a spin triplet (S=1) configuration can be obtained when monitoring the emission under resonant excitation. This observation can be explained by non-radiative recombination via a lower lying excited triplet state. In strained samples all no-phonon PL lines are split into a series of lines. For the highest energy lines the main splitting can be attributed to lifting of the orbital degeneracy of the excited states, the additional broadening or splitting is probably due to a strain distribution in the samples.
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