| 1. |
- Tien Son, Nguyen, et al.
(författare)
-
Negative-U System of Carbon Vacancy in 4H-SiC
- 2012
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 109:18, s. 187603-
-
Tidskriftsartikel (refereegranskat)abstract
- Using electron paramagnetic resonance (EPR), energy levels of the carbon vacancy (V-C) in 4H-SiC and its negative-U properties have been determined. Combining EPR and deep-level transient spectroscopy we show that the two most common defects in as-grown 4H-SiC-the Z(1/2) lifetime-limiting defect and the EH7 deep defect-are related to the double acceptor (2 - vertical bar 0) and single donor (0 vertical bar +) levels of V-C, respectively.
|
|
| 2. |
- Beyer, Franziska, et al.
(författare)
-
Annealing behavior of the EB-centers and M-center in low-energy electron irradiated n-type 4H-SiC
- 2011
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 109:10, s. 103703-
-
Tidskriftsartikel (refereegranskat)abstract
- After low-energy electron irradiation of epitaxial n-type 4H-SiC with a dose of 5 x 10(16) cm(-2), the bistable M-center, previously reported in high-energy proton implanted 4H-SiC, is detected in the deep level transient spectroscopy (DLTS) spectrum. The annealing behavior of the M-center is confirmed, and an enhanced recombination process is suggested. The annihilation process is coincidental with the evolvement of the bistable EB-centers in the low temperature range of the DLTS spectrum. The annealing energy of the M-center is similar to the generation energy of the EB-centers, thus partial transformation of the M-center to the EB-centers is suggested. The EB-centers completely disappeared after annealing temperatures higher than 700 degrees C without the formation of new defects in the observed DLTS scanning range. The threshold energy for moving Si atom in SiC is higher than the applied irradiation energy, and the annihilation temperatures are relatively low, therefore the M-center, EH1 and EH3, as well as the EB-centers are attributed to defects related to the C atom in SiC, most probably to carbon interstitials and their complexes.
|
|
| 3. |
- Beyer, Franziska, et al.
(författare)
-
Bistable defects in low-energy electron irradiated n-type 4H-SiC
- 2010
-
Ingår i: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS. - : John Wiley and Sons, Ltd. - 1862-6254. ; 4:8-9, s. 227-229
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial n-type 4H-SiC layers were irradiated at room temperature by low-energy electrons. During the annihilation process of the irradiation induced defects EH I and EH3, three new bistable centers, labeled EB centers, were detected in the DLTS spectrum. The reconfigurations of the EB centers (I -andgt; II and II -andgt; I) take place at room temperature with a thermal reconfiguration energy of about 0.95 eV. The threshold energy for moving the Si atom from its site in the SiC crystal structure is higher than the applied irradiation energy; therefore, the EB centers are attributed to carbon related complex defects.
|
|
| 4. |
- Beyer, Franziska, et al.
(författare)
-
Capacitance transient study of a bistable deep level in e(-)-irradiated n-type 4H-SiC
- 2012
-
Ingår i: Journal of Physics D. - : Institute of Physics. - 0022-3727 .- 1361-6463. ; 45:45
-
Tidskriftsartikel (refereegranskat)abstract
- Using capacitance transient techniques, a bistable centre, called FB centre here, was observed in electron irradiated 4H-SiC. In configuration A, the deep level known as EH5 (E-a = E-C - 1.07 eV) is detected in the deep level transient spectroscopy spectrum, whereas for configuration B no obvious deep level is observed in the accessible part of the band gap. Isochronal annealing revealed the transition temperatures to be T-A -andgt; B andgt; 730K and for the opposite process T-B -andgt; A approximate to 710 K. The energy needed to conduct the transformations were determined to be E-A(A -andgt; B) = (2.1 +/- 0.1) eV and E-A(B -andgt; A) = (2.3 +/- 0.1) eV, respectively. The pre-factor indicated an atomic jump process for the opposite transition A -andgt; B and a charge carrier-emission dominated process in the case of B -andgt; A. Minority charge carrier injection enhanced the transformation from configuration B to configuration A by lowering the transition barrier by about 1.4 eV. Since the bistable FB centre is already present after low-energy electron irradiation (200 keV), it is likely related to carbon.
|
|
| 5. |
- Beyer, Franziska, et al.
(författare)
-
Defects in low-energy electron-irradiated n-type 4H-SiC
- 2010
-
Ingår i: Physica Scripta, vol. T141. - : IOP Publishing. ; , s. 014006-
-
Konferensbidrag (refereegranskat)abstract
- The bistable M-center, previously observed in high-energy proton-implanted 4H-SiC, was detected in low-energy electron-irradiated 4H-SiC using deep-level transient spectroscopy (DLTS). Irradiation increased the DLTS signals of the intrinsic defects Z(1/2) and EH6/7 and introduced the frequently observed defects EH1 and EH3. After the M-center is annealed out at about 650K without bias and at about 575K with bias applied to the sample during the annealing process, a new bistable defect in the low temperature range of the DLTS spectrum, the EB-center, evolves. Since low-energy irradiation affects mainly the carbon atoms in SiC, the M-center and the newly discovered EB-center are most probably carbon-related intrinsic defects.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Carlsson, Patrick, et al.
(författare)
-
Deep levels in low-energy electron-irradiated 4H-SiC
- 2009
-
Ingår i: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS. - : Wiley. - 1862-6254. ; 3:4, s. 121-123
-
Tidskriftsartikel (refereegranskat)abstract
- Deep levels introduced by low-energy (200 keV) electron irradiation in n-type 4H-SiC epitaxial layers grown by chemical vapour deposition were studied by deep level transient spectroscopy (DLTS) and photoexcitation electron paramagnetic resonance (photo-EPR). After irradiation, several DLTS levels, EH1, EH3, Z(1/2), EH5 and EH6/7, often reported in irradiated 4H-SiC, were observed. In irradiated freestanding films from the same wafer, the EPR signals of the carbon vacancy in the positive and negative charge states, V-C(+) and V-C(-), respectively, can be observed simultaneously under illumination with light of certain photon energies. Comparing the ionization energies obtained from DLTS and photo-EPR, we suggest that the EH6/7 (at similar to E-C - 1.6 eV) and EH5 (at similar to E-C - 1.0 eV) electron traps may be related to the single donor (+ vertical bar 0) and the double acceptor (1- vertical bar 2-) level of V-C, respectively. Judging from the relative intensity of the DLTS signals, the EH6/7 level may also be contributed to by other unidentified defects.
|
|
| 9. |
- Carlsson, Patrick, 1975-, et al.
(författare)
-
Electron paramagnetic resonance study on n-type electron-irradiated 3C-SiC
- 2008
-
Ingår i: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - BRISTOL, ENGLAND : IOP PUBLISHING LTD.
-
Konferensbidrag (refereegranskat)abstract
- Electron Paramagnetic Resonance (EPR) was used to study defects in n-type 3C-SiC films irradiated by 3-MeV electrons at room temperature with a dose of 2x10(18) cm(-2). After electron irradiation, two new EPR spectra with an effective spin S = 1, labeled L5 and L6, were observed. The L5 center has C-3v symmetry with g = 2.004 and a fine-structure parameter D = 436.5 x 10(-4) cm(-1). The L5 spectrum was only detected under light illumination and it could not be detected after annealing at similar to 550 C. The principal z-axis of the D tensor is parallel to the < 111 >-directions, indicating the location of spins along the Si-C bonds. Judging from the symmetry and the fact that the signal was detected under illumination in n-type material, the L5 center may be related to the divacancy in the neutral charge state. The L6 center has a C-2v-symmetry with an isotropic g-value of g=2.003 and the fine structure parameters D=547.7 x 10(-4) cm-1 and E=56.2 x 10(-4) cm(-1). The L6 center disappeared after annealing at a rather low temperature (similar to 200 degrees C), which is substantially lower than the known annealing temperatures for vacancy-related defects in 3C-SiC. This highly mobile defect may be related to carbon interstitials.
|
|
| 10. |
- Carlsson, Patrick, 1975-, et al.
(författare)
-
EPR and ab initio calculation study on the EI4 center in 4H and 6H-SiC
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:23, s. 235203-
-
Tidskriftsartikel (refereegranskat)abstract
- We present new results from electron paramagnetic resonance (EPR) studies of the EI4 EPR center in 4H- and 6H-SiC. The EPR signal of the EI4 center was found to be drastically enhanced in electron-irradiated high-purity semi-insulating materials after annealing at 700-750°C. Strong EPR signals of the EI4 center with minimal interferences from other radiation-induced defects in irradiated high-purity semiinsulating materials allowed our more detailed study of the hyperfine (hf) structures. An additional large-splitting 29Si hf structure and 13C hf lines of the EI4 defect were observed. Comparing the data on the defect formation, the hf interactions and the annealing behavior obtained from EPR experiments and from ab initio supercell calculations of different carbon-vacancy related complexes, we suggest a complex between a carbon vacancy-carbon antisite and a carbon vacancy at the third neighbor site of the antisite in the neutral charge state, (VC-CSiVC)0, as a new defect model for the EI4 center.
|
|
| 11. |
- Carlsson, Patrick, 1975-, et al.
(författare)
-
Photo-EPR Studies on Low-Energy Electron-irradiated 4H-SiC
- 2009
-
Ingår i: Materials Science Forum, Vols. 615-617. - Materials Science Forum Vols. 615-617 : Trans Tech Publications. - 9780878493340 ; , s. 401-404
-
Konferensbidrag (refereegranskat)abstract
- Photoexcitation electron paramagnetic resonance (photo-EPR) was used to determine deep levels related to the carbon vacancy (VC) in 4H-SiC. High-purity free-standing n-type 4H-SiC epilayers with concentration of intrinsic defects (except the photo-insensitive SI1 center) below the detection limit of EPR were irradiated with low-energy (200 keV) electrons to create mainly VC and defects related to the C sublattice. The simultaneous observation of and signals, their relative intensity changes and the absence of other defects in the sample provide a more straight and reliable interpretation of the photo-EPR results. The study suggests that the (+|0) level of VC is located at ~EC–1.77 eV in agreement with previously reported results and its single and double acceptor levels may be at ~ EC–0.8 eV and ~ EC–1.0 eV, respectively.
|
|
| 12. |
- Carlsson, Patrick, et al.
(författare)
-
Silicon antisite related defects in electron-irradiated p-type 4H- and 6H-SiC
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The electron paramagnetic resonance (EPR) LE5 centers were previously observed in electron-irradiated p-type 4H- and 6H-SiC but have not been identified due to lack of experimental data. In this study, two different Si hyperfine (hf) structures of the LE5 centers have been detected and the corresponding hf tensors have been determined. One structure is due to a very anisotropic hf interaction with one Si atom and the other structure to the hf interaction with two neighboring Si atoms in the basal plane. The obtained g values and Si hf constants are in good agreement with calculated parameters reported for antisite pairs in 4H-SiC. Based on the similarity in the spin-Hamiltonian parameters, the LE5 centers may be the antisite pairs in the positive charge state.
|
|
| 13. |
- Carlsson, Patrick, 1975-, et al.
(författare)
-
The EI4 EPR centre in 6H SiC
- 2010
-
Ingår i: Physica Scripta, Vol. T141. - : IOP Publishing. ; , s. 014013-
-
Konferensbidrag (refereegranskat)abstract
- We present the results of our recent electron paramagnetic resonance (EPR) studies of the EI4 EPR centre in electron-irradiated high-purity semi-insulating 6H SiC. Higher signal intensities and better resolution compared with previous studies have enabled a more detailed study of the hyperfine (hf) structure. Based on the observed hf structure due to the interaction with Si and C neighbours, the effective spin S = 1, the C-1h-symmetry and the annealing behaviour, we suggest a carbon vacancy-carbon antisite complex in the neutral charge state, VCVCCSi0, with the vacancies and the antisite in the basal plane, as a new defect model for the centre.
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
- Isoya, J., et al.
(författare)
-
EPR Identification of Defects and Impurities in SiC : To Be Decisive
- 2009
-
Ingår i: Materials Science Forum, Vols. 600-603. - : Trans Tech Publications. ; , s. 279-284
-
Konferensbidrag (refereegranskat)abstract
- In EPR (electron paramagnetic resonance) identification of point defects, hyperfine (HF) interaction is decisive information not only for chemical identity but also for the local geometry and the electronic state. In some intrinsic defects in SiC, the wave function of the unpaired electron extends quite unevenly among major atoms comprising the defects. In such a case, the determination of the number of equivalent atoms and the chemical identity (Si or C) of those atoms even with weak HF splitting are useful to compare with HF parameters obtained theoretically. For vacancy-related defects of relatively deep levels, the sum of the spin densities on the nearest-neighbor shell is found to be 60-68%.
|
|
| 17. |
|
|
| 18. |
- Isoya, J., et al.
(författare)
-
EPR identification of intrinsic defects in SiC
- 2008
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 245:7, s. 1298-1314
-
Tidskriftsartikel (refereegranskat)abstract
- The structure determination of intrinsic defects in 4H-SiC, 6H-SiC, and 3C-SiC by means of EPR is based on measuring the angular dependence of the 29Si/13C hyperfine (HF) satellite lines, from which spin densities, sp-hybrid ratio, and p-orbital direction can be determined over major atoms comprising a defect. In most cases, not only the assignment of the variety due to the inequivalent sites (h- and k-sites in 4H-SiC) but also the identification of the defect species is accomplished through the comparison of the obtained HF parameters with those obtained from first principles calculations. Our works of identifying vacancy-related defects such as the monovacancies, divacancies, and antisite-vacancy pairs in 4H-SiC are reviewed. In addition, it is demonstrated that the observation of the central line of the TV2a center of S = 3/2 has been achieved by pulsed-ELDOR. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.
|
|
| 19. |
- Isoya, J, et al.
(författare)
-
Pulsed EPR studies of phosphorus shallow donors in diamond and SiC
- 2006
-
Ingår i: Physica B, Vols. 376-377. - : Elsevier BV. ; , s. 358-361
-
Konferensbidrag (refereegranskat)abstract
- Phosphorus shallow donors having the symmetry lower than T-d are studied by pulsed EPR. In diamond:P and 3C-SiC:P, the symmetry is lowered to D-2d and the density of the donor wave function on the phosphorus atom exhibits a predominant p-character. In 4H-SiC:P with the site symmetry of C-3v, the A(1) ground state of the phosphorus donors substituting at the quasi-cubic site of silicon shows an axial character of the distribution of the donor wave function in the vicinity of the phosphorus atom. (c) 2005 Elsevier B.V. All rights reserved.
|
|
| 20. |
|
|
| 21. |
- Janzén, Erik, 1954-, et al.
(författare)
-
Defects in SiC
- 2004
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 22. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
-
Defects introduced by electron-irradiation at low temperatures in SiC
- 2009
-
Ingår i: Materials Science Forum Vols. 615-617. - : Trans Tech Publicarions. - 9780878493340 ; , s. 377-380
-
Konferensbidrag (refereegranskat)abstract
- Defects introduced by electron irradiation at ~80-100 K in 3C-, 4H- and 6H-SiC were studied by electron paramagnetic resonance (EPR). A number of EPR spectra, labelled LE1-10, were detected. Combining EPR and supercell calculations, we will show that the LE1 center in 3C-SiC with C2v symmetry and an electron spin S=3/2 is related to the (VSi-Sii)3+ Frenkel pair between the silicon vacancy and a second neighbour Sii interstitial along the <100> direction. Results on other centers, possibly also related to interstitials, are discussed.
|
|
| 23. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
-
Divacancy in 4H-SiC
- 2006
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 96:5, s. 055501-1-055501-4
-
Tidskriftsartikel (refereegranskat)abstract
- Electron paramagnetic resonance and ab initio supercell calculations suggest that the P6/P7 centers, which were previously assigned to the photoexcited triplet states of the carbon vacancy-antisite pairs in the double positive charge state, are related to the triplet ground states of the neutral divacancy. The spin density is found to be located mainly on three nearest C neighbors of the silicon vacancy, whereas it is negligible on the nearest Si neighbors of the carbon vacancy.
|
|
| 24. |
|
|
| 25. |
|
|
| 26. |
|
|
| 27. |
- Nguyen, Son Tien, et al.
(författare)
-
Identification of a Frenkel-pair defect in electron-irradiated 3C SiC
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80, s. 125201-
-
Tidskriftsartikel (refereegranskat)abstract
- Anelectron paramagnetic resonance (EPR) spectrum labeled LE1 was observed inn-type 3C SiC after electron irradiation at low temperatures (~80–100 K).A hyperfine interaction with four nearest C neighbors similar tothat of the well-known silicon vacancy in the negative chargestate was observed, but the LE1 center has a lowersymmetry, C2v. Supercell calculations of different configurations of silicon vacancy-interstitialFrenkel-pairs, VSi-Sii, were performed showing that pairs with a nearestneighbor Si interstitial are unstable—VSi and Sii will automatically recombine—whereaspairs with a second neighbor Sii are stable. Comparing thedata obtained from EPR and supercell calculations, the LE1 centeris assigned to the Frenkel-pair between VSi and a secondneighbor Sii interstitial along the [100] direction in the 3+charge state, V-Si. In addition, a path for the migrationof Si was found in 3C SiC. In samples irradiatedat low temperatures, the LE1 Frenkel-pair was found to bethe dominating defect whereas EPR signals of single vacancies werenot detected. The center disappears after warming up the samplesto room temperature.
|
|
| 28. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
-
Magnetic resonance studies of defects in electron-irradiated ZnO substrates
- 2007
-
Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 401-402, s. 507-510
-
Tidskriftsartikel (refereegranskat)abstract
- Optical detection of magnetic resonance (ODMR) was used to study defects in electron-irradiated ZnO substrates. In addition to the shallow donor and the Zn vacancy, several ODMR centers with an effective electron spin were detected. Among these, the axial LU3 and non-axial LU4 centers are shown to be dominating recombination centers. The annealing behavior of radiation-induced defects was studied and possible defect models are discussed.
|
|
| 29. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
-
Recombination centers in as-grown and electron-irradiated ZnO substrates
- 2007
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:9
-
Tidskriftsartikel (refereegranskat)abstract
- Optical detection of magnetic resonance (ODMR) was used to study defects in ZnO substrates irradiated with 3 MeV electrons at room temperature. The Zn vacancy and some other ODMR centers were detected. Among these, the Zn vacancy and two other centers, labeled as LU3 and LU4, were also commonly observed in different types of as-grown ZnO substrates. The LU3 and LU4 are related to intrinsic defects and act as dominating recombination centers in irradiated and as-grown ZnO. © 2007 American Institute of Physics.
|
|
| 30. |
- Nguyen, Tien Son, et al.
(författare)
-
Identification of divacancies in 4H-SiC
- 2006
-
Ingår i: Physica B: Condensed Matter, Vols. 376-377. - : Elsevier BV. ; , s. 334-337
-
Konferensbidrag (refereegranskat)abstract
- The P6/P7 centers in 4H-SiC were studied by electron paramagnetic resonance (EPR) and ab initio supercell calculations. The hyperfine coupling constants of C and Si neighbors obtained by EPR are in good agreement with the calculated values for the neutral divacancy, VCVsi0. Our results suggest that the P6/P7 centers, which were previously assigned to the photo-excited triplet states of the carbon vacancy-carbon antisite pairs in the double positive charge state (VCCsi2+), are related to the triplet ground states of the C-3v/C-1h si configurations of VCVsi0 (c) 2006 Elsevier B.V. All rights reserved.
|
|
| 31. |
- Nguyen, Tien Son, et al.
(författare)
-
Identification of the gallium vacancy-oxygen pair defect in GaN
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80:15, s. 153202-
-
Tidskriftsartikel (refereegranskat)abstract
- Cation vacancies like VGa, VAl and their complexes with oxygen are predicted to be abundant in III-nitrides and to play an important role in nonradiative recombination. Appearing in triple or double negatively charged states, they are not paramagnetic and have not so far been detected by magnetic resonance even under illumination. In this Brief Report, we demonstrate an efficient way to make cation vacancy defects in GaN detectable by electron paramagnetic resonance and present our identification of the VGaON pair in GaN which is the model material for the III-nitrides and their alloys.
|
|
| 32. |
- Nguyen, Tien Son, et al.
(författare)
-
The carbon vacancy related EI4 defect in 4H-SiC
- 2010
-
Ingår i: Materials Science Forum. Vols. 645-648. - : Trans Tech Publications. ; , s. 399-402
-
Konferensbidrag (refereegranskat)abstract
- Electron paramagnetic resonance (EPR) was used to study high-purity semi-insulating 4H-SiC irradiated with 2 MeV electrons at room temperature. The EPR signal of the EI4 defect was found to be dominating in samples irradiated and annealed at 750 C. Additional large-splitting Si-29 hyperfine (hf) lines and also other C-13 and Si-29 hf structures were observed. Based on the observed hf structures and annealing behaviour, the complex between a negative carbon vacancy-carbon antisite pair (VCCSi-) and a distance positive carbon vacancy (V-C(+)) is tentatively proposed as a possible model for the EIO4 defect.
|
|
| 33. |
- Son, Nguyen Tien, et al.
(författare)
-
EPR and ENDOR Studies of Shallow Donors in SiC
- 2010
-
Ingår i: Applied Magnetic Resonance. - : Elsevier B.V. - 0937-9347 .- 1613-7507. ; 39:1-2, s. 49-85
-
Tidskriftsartikel (refereegranskat)abstract
- Recent progress in the investigation of the electronic structure of the shallow nitrogen (N) and phosphorus (P) donors in 3C–, 4H– and 6H–SiC is reviewed with focus on the applications of magnetic resonance including electron paramagnetic resonance (EPR) and other pulsed methods such as electron spin echo, pulsed electron nuclear double resonance (ENDOR), electron spin-echo envelope modulation and two-dimensional EPR. EPR and ENDOR studies of the 29Si and 13C hyperfine interactions of the shallow N donors and their spin localization in the lattice are discussed. The use of high-frequency EPR in combination with other pulsed magnetic resonance techniques for identification of low-temperature P-related centers in P-doped 3C–, 4H– and 6H–SiC and for determination of the valley–orbit splitting of the shallow N and P donors are presented and discussed.
|
|
| 34. |
- Son, Nguyen Tien, et al.
(författare)
-
Hydrogen at zinc vacancy of ZnO : an EPR and ESEEM study
- 2014
-
Ingår i: International Conference on Defects in Semiconductors 2013. - : American Institute of Physics (AIP). - 9780735412156 ; , s. 341-344
-
Konferensbidrag (refereegranskat)abstract
- An electron paramagnetic resonance (EPR) spectrum, labeled S1, with small-splitting doublet accompanied by weak satellites is observed in ZnO irradiated with 2 MeV electrons. The obtained structure is shown to be the hyperfine structure due to the dipolar interaction between an unpaired electron spin and a nuclear spin of hydrogen (H). The observation of the nuclear Zeeman frequency of H in electron spin echo envelope modulation experiments further confirmed the presence of a hydrogen atom in S1. From the observed spin-Hamiltonian parameters, S1 is identified to be the partly H-passivated Zn vacancy,V-Zn(-) H+, with the H+ ion making a short O-H bond with only one nearest O neighbor of V-Zn in the basal plane, being off the substitutional site, while the unpaired electron spin, which gives rise to the observed EPR signal, is localized on the p orbital of another O neighbor also in the basal plane.
|
|
| 35. |
- Son, N. T., et al.
(författare)
-
Magnetic resonance identification ofhydrogen at a zinc vacancy in ZnO
- 2013
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25, s. 335804-
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen (H) at a zinc vacancy (VZn) in ZnO is identified by electron paramagnetic resonance(EPR) and electron spin echo envelope modulation (ESEEM). In ZnO irradiated by 2 MeVelectrons, a doublet EPR spectrum, labelled S1, is observed. The doublet structure and theaccompanying weak satellites are shown to be the allowed and forbidden lines of the hyperfinestructure due to the dipolar interaction between an electron spin S D 1=2 and a nuclear spinI D 1=2 of 1H located at a VZn. The involvement of a single H atom in the S1 defect is furtherconfirmed by the observation of the nuclear Zeeman frequency of 1H in ESEEM experiments.We show that at a VZn, H prefers to make a short O–H bond with one O neighbour and is offthe substitutional site, forming a low symmetry C1 defect. In this partly H passivated VZn, the unpaired electron localizes on the p orbital of another O neighbour of VZn, and not on the H.
|
|
| 36. |
- Son, Nguyen Tien, et al.
(författare)
-
Radiation-induced defects in GaN
- 2010
-
Ingår i: Physica Scripta, Vol. T141. - : IOP Publishing. ; , s. 014015-
-
Konferensbidrag (refereegranskat)abstract
- Radiation-induced defects in n-type GaN irradiated by 2 MeV electrons at room temperature were studied by electron paramagnetic resonance (EPR). Four EPR spectra, labelled D1-D4, were observed in irradiated n-type GaN. The D1 spectrum is a broad line (similar to 10-12 mT in line width) with an isotropic g-value g similar to 2.03 and can be detected in all the studied samples in the temperature range of 4-300 K. The D2 centre has an electron spin S = 1/2 and shows a clear hyperfine structure due to interaction with three equivalent N-14. The g-values of the axial configuration are determined to be g(parallel to) = 2.001 and g(perpendicular to) = 1.999. On the basis of the observed hyperfine structure, formation conditions and annealing behaviour, the D2 defect was assigned to the gallium vacancy-oxygen pair in the negative charge state, (VGaON)(-).
|
|
| 37. |
- Son Tien, Nguyen, et al.
(författare)
-
Defects at nitrogen site in electron-irradiated AlN
- 2011
-
Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 98:24, s. 242116-
-
Tidskriftsartikel (refereegranskat)abstract
- In high resistance AlN irradiated with 2 MeV electrons, an electron paramagnetic resonance (EPR) spectrum, labeled EI-1, with an electron spin S=1/2 and a clear hyperfine (hf) structure was observed. The hf structure was shown to be due the interaction between the electron spin and the nuclear spins of four (27)A nuclei with the hf splitting varying between similar to 6.0 and similar to 7.2 mT. Comparing the hf data obtained from EPR and ab initio supercell calculations we suggest the EI-1 defect to be the best candidate for the neutral nitrogen vacancy in AlN.
|
|
| 38. |
- Umeda, T, et al.
(författare)
-
Dicarbon antisite defect in n-type 4H-SiC
- 2009
-
Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 79:11, s. 115211-
-
Tidskriftsartikel (refereegranskat)abstract
- We identify the negatively charged dicarbon antisite defect (C-2 core at silicon site) in electron-irradiated n-type 4H-SiC by means of combined electron paramagnetic resonance (EPR) measurements and first-principles calculations. The HEI5 and HEI6 EPR centers (S=1/2; C-1h symmetry) are associated with cubic and hexagonal dicarbon antisite defects, respectively. This assignment is based on a comparison of the measured and calculated hyperfine tensors of C-13 and Si-29 atoms as far as the second neighborhood around the defects. Theoretically, the dicarbon antisites are stable in a single negative charge state under a wide range of n-type samples. We found that the defects can be created under a wide range of irradiation conditions, and our measurements strongly suggest the existence of carbon antisite defects in the as-grown samples. Annealing studies revealed several atomistic processes such as recombination of carbon interstitials with vacancies and formation of carbon aggregates. These processes were activated at about 1000 degrees C, and as theoretically predicted, the dicarbon antisite is much more stable than the dicarbon interstitial defect (C-2 core at carbon site). The measured activation temperature is consistent with the temperature range for forming various carbon aggregate-related photoluminescence centers.
|
|
| 39. |
|
|
| 40. |
- Umeda, T., et al.
(författare)
-
EPR and theoretical studies of positively charged carbon vacancy in 4H-SiC
- 2004
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 70:23
-
Tidskriftsartikel (refereegranskat)abstract
- The carbon vacancy is a dominant defect in 4H-SiC, and the "E15" electron-paramagnetic-resonance (EPR) spectrum originates from positively charged carbon vacancies (VC+) at quasicubic sites. The observed state for EI5, however, has been attributed to a motional-averaged state with the C3v symmetry, and its true atomic structure has not been revealed so far. We here report low temperature (
|
|
