| 1. |
- Lorenzzi, J., et al.
(författare)
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Incorporation of group III, IV and V elements in 3C–SiC(1 1 1) layers grown by the vapour–liquid–solid mechanism
- 2010
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 312:23, s. 3443-3450
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Tidskriftsartikel (refereegranskat)abstract
- We report on a comparative investigation of the incorporation of group III, IV and V impurities in 3C–SiC heteroepitaxial layers grown by the vapour–liquid–solid (VLS) mechanism on on-axis α-SiC substrates. To this end, various Si-based melts have been used with addition of Al, Ga, Ge and Sn species. Homoepitaxial α-SiC layers grown using Al-based melts were used for comparison purposed for Al incorporation. Nitrogen incorporation depth profile systematically displays an overshoot at the substrate/epilayer interface for all the layers. Ga and Al incorporations follow the same distribution shape as N whereas this is not the case for the isoelectronic impurities Ge and Sn. This suggests some interaction between Ga/Al and N coming from the high bonding energy between the group III and V elements, which does not exist with Ge and Sn. This is why both incorporate as a cluster. A model of incorporation is proposed taking into account metal-N and metal-C bonding energies together with the solid solubility of the corresponding nitrides.
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| 2. |
- Sun, J. W., et al.
(författare)
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Combined effects of Ga, N, and Al codoping in solution grown 3C-€“SiC
- 2010
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108:1, s. 013503-1-013503-10
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Tidskriftsartikel (refereegranskat)abstract
- We report on Ga-doped 3C–SiC epitaxial layers grown on on-axis (0001) 6H–SiC substrates using the vapor-liquid-solid technique and different melts. The resulting samples have been investigated using secondary ion mass spectroscopy(SIMS), micro-Raman spectroscopy and, finally, low temperature photoluminescence (LTPL) spectroscopy. From SIMS measurements we find Ga concentrations in the range of , systematically accompanied by high nitrogen content. In good agreement with these findings, the spectra show that the Ga-doped samples are -type, with electron concentrations close to . As expected, the LTPL spectra are dominated by strong N–Ga donor-acceptor pair (DAP) transitions. In one sample, a weak additional N–Al DAP recombination spectrum is also observed, showing the possibility to have accidental codoping with Ga and Al simultaneously. This was confirmed on a non-intentionally doped 3C–SiC (witness) sample on which, apart of the usual N and Al bound exciton lines, a small feature resolved at 2.35 eV comings from neutral Ga bound excitons. Quantitative analyses of the DAP transition energies in the Ga-doped and witness sample gave 346 meV for the optical binding energy of Ga acceptors in 3C–SiC against 251 meV for the Al one. The conditions for the relative observa-tion of Ga and Al related LTPL features are discussed and the demonstration of room temperature luminescence using Ga doping is done.
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| 3. |
- Sun, J. W., et al.
(författare)
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LTPL Investigation of N-Ga and N-Al Donor-Acceptor Pair Spectra in 3C-SiC Layers Grown by VLS on 6H-SiC Substrates
- 2010
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Ingår i: Silicon Carbide and Related Materials 2009. ; , s. 415-418
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Konferensbidrag (refereegranskat)abstract
- Ga-doped 3C-SiC layers have been grown on on-axis 6H-SiC (0001) substrates by the VLS technique and investigated by low temperature photoluminescence (LTPL) measurements. On these Ga-doped samples, all experimental spectra collected at 5K were found dominated by strong N-Ga donor-acceptor pair (DAP) transitions and phonon replicas. As expected, the N-Ga DAP zero-phonon line (ZPL) was located at lower energy ( 86 meV) below the N-Al one. Fitting the transition energies for the N-Al close DAP lines gave 251 meV for the Al acceptor binding energy in 3C-SiC and, by comparison, 337 meV for the Ga acceptor one.
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| 4. |
- Sun, J. W., et al.
(författare)
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Splitting of close N-€Al donor-€acceptor-€pair spectra in 3C-€SiC
- 2010
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Konferensbidrag (refereegranskat)abstract
- Discrete series of lines have been observed for many years in N‐Al DAP (Donor Acceptor Pair) spectra in 3C‐SiC. Unfortunately, up to now, there has been no quantitative analysis for the splitting of lines in a given shell. This is done in this work for N‐Al DAP spectra in 3C‐SiC. The samples were non‐intentionally doped 3C‐SiC layers grown by CVD on a VLS seeding layer grown on a 6H‐SiC substrate. From low temperature photoluminescence measurements, strong N‐Al DAP emission bands were observed and, on the high energy side of the zero‐phonon line, we could resolve a series of discrete lines coming from close pairs. Comparing with literature data, we show that the splitting energy for a given shell is constant and, to explain this shell substructure, we consider the non equivalent sets of sites for a given shell. Results are discussed in terms of the ion‐ion interaction containing third and forth multipole terms.
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| 5. |
- Zoulis, G., et al.
(författare)
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Effects of Growth Conditions on the Low Temperature Photoluminescence Spectra of (111) 3C-€SiC Layers Grown by Chemical Vapor Deposition on 3C-€SiC Seeds grown by the Vapor-€Liquid-Solid Technique
- 2010
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X.
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Konferensbidrag (refereegranskat)abstract
- We report the results of a low temperature photoluminescence investigation of 3C‐SiC samples grown by chemical vapor deposition on vapor‐liquid‐solid seeds. The main parameters tested in this series of samples were i°) the effects of changing the C/Si ratio and ii°) the growth temperature on the final growth product. On the first series the C/Si ratio varied from 1 to 14 for a constant growth temperature of 1550° C. For the second series, the growth temperature varied from 1450 to 1650° C by steps of 50° C with a constant C/Si ratio equal to 3. According to this work, the best results (minimum incorporation of impurities and best crystal quality) were obtained when using a C/Si ratio of 3 at 1650° C.
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| 6. |
- Marinova, Maya, et al.
(författare)
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Structural and Optical Investigation of VLS Grown (111) 3C-SiC Layers on 6H-SiC Substrates in Sn-Based Melts
- 2011
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Ingår i: Silicon Carbide and Related Materials 2010. ; , s. 165-168
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Konferensbidrag (refereegranskat)abstract
- The current communication focuses on the investigation of 3C-SiC layers grown by the Vapour-Liquid-Solid mechanism on on-axis Si-face 6H-SiC substrates in SiSn melts with different compositions and at different growth temperatures. The layers are studied by Transmission Electron Microscopy and Low Temperature Photoluminescence. It was found that for melts with Sn concentration higher than 60 at% large Sn-related precipitates are formed. The depth distribution of the Sn precipitates strongly depends not only on the melt composition but also on the growth temperature. Their formation strongly influences the stacking fault density and the dopant incorporation in the layers. Lower Sn concentrations combined with higher growth temperatures should result in 3C-SiC layer with enhanced structural quality.
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| 7. |
- Sonde, S, et al.
(författare)
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Electrical properties of the graphene/4H-SiC (0001) interface probed by scanning current spectroscopy
- 2009
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Ingår i: PHYSICAL REVIEW B. - 1098-0121. ; 80:24, s. 241406-
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Tidskriftsartikel (refereegranskat)abstract
- The current transport across the graphene/4H-SiC interface has been investigated with nanometric lateral resolution by scanning current spectroscopy on both epitaxial graphene (EG) grown on (0001) 4H-SiC and graphene exfoliated from highly oriented pyrolytic graphite deposited on the same substrate [deposited graphene (DG)]. This study reveals that the Schottky barrier height (SBH) of EG/4H-SiC (0.36 +/- 0.1 eV) is similar to 0.49 eV lower than the SBH of DG/4H-SiC (0.85 +/- 0.06 eV). This result is discussed in terms of the Fermi-level pinning similar to 0.49 eV above the Dirac point in EG due to the presence of positively charged states at the interface between the Si face of 4H-SiC and the carbon-rich buffer layer, which is the precursor for EG formation.
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| 8. |
- Vasiliauskas, Remigijus, et al.
(författare)
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Effect of initial substrate conditions on growth of cubic silicon carbide
- 2011
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Ingår i: Journal of Crystal Growth. - : Elsevier Science B.V., Amsterdam.. - 0022-0248 .- 1873-5002. ; 324:1, s. 7-14
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Tidskriftsartikel (refereegranskat)abstract
- In order to analyze the epitaxial growth of cubic silicon carbide by sublimation epitaxy on different substrates, four different 6H-SiC substrate preparations were used: (i) as-received, (ii) re-polished, (iii) annealed and covered by silicon layer and (iv) with (1 1 1) 3C-SiC buffer layer. Almost 100% coverage and low twin density was achieved when grown on the buffer layer. The XRD and TEM characterizations show better material quality when the layer is grown directly on 6H-SiC substrates. Background doping evaluated by LTPL is in the range of 10(16) cm(-3) for N and 10(16) cm(-3) for Al in all grown layers.
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| 9. |
- Zoulis, G., et al.
(författare)
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Seeding layer influence on the low temperature photoluminescence intensity of 3C-SiC grown on 6H-SiC by sublimation epitaxy
- 2012
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Ingår i: HETEROSIC and WASMPE 2011. - : Trans Tech Publications Inc.. ; , s. 149-153
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Konferensbidrag (refereegranskat)abstract
- We report on n-type 3C-SiC samples grown by sublimation epitaxy. We focus on the low temperature photoluminescence intensity and show that the presence of a first conversion layer, grown at low temperature, is not only beneficial to improve the homogeneity of the polytype conversion but, also, to the LTPL signal intensity. From the use of a simple model, we show that this comes from a reduced density of non-radiative recombination centers.
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| 10. |
- Marinova, Maya, et al.
(författare)
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Influence of Post-Growth Annealing on the Defects Nature and Distribution in VLS Grown (111) 3C-SiC Layers
- 2011
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Ingår i: Silicon Carbide and Related Materials 2010. ; , s. 241-244
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Konferensbidrag (refereegranskat)abstract
- The current communication focuses on the influence of a post-growth annealing on the evolution of defects inside (111) 3C-SiC layers grown by the Vapour Liquid Solid (VLS) mechanism in SiGe melts on Si-face on- and off axis 6H-SiC substrates. The layers are studied by Transmission Electron Microscopy (TEM) and Low Temperature Photoluminescence (LTPL). It was found that the growth on off-axis substrates results in a 3C-SiC layer containing mainly stacking faults (SFs) and microtwins (MT). The density of MT lamellae and SFs reduces in the layers grown on the on-axis substrate compared to off-axis substrate. In the layers grown on off-axis substrates the annealing strongly reduces the density of SFs inclined to the 3C/6H-SiC interface. Additionally, 3C to 6H polytypic transformation appears only at the interface, most probably starting from substrate step edges. This was only seen on off-axis seed since the step edges are more.
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| 11. |
- Robert, T., et al.
(författare)
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6H-type zigzag faults in low-doped 4H-SiC epitaxial layers.
- 2010
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Ingår i: Mat. Sci. Forum, Vols. 645-648. - 0878492798 - 9780878492794 ; , s. 347-350
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Konferensbidrag (refereegranskat)abstract
- A new type of 6H zigzag faults has been identified from high resolution transmission electron microscopy (HRTEM) measurements performed on low-doped 4H-SiC homoepitaxial layer grown on off-axis substrates in a hot-wall CVD reactor. They are made of half unit cells of 6H with corresponding low temperature photoluminescence (LTPL) response ranging from about 3 eV to 2.5 eV at liquid helium temperature.
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| 12. |
- Sun, Jianwu, et al.
(författare)
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Low Temperature Photoluminescence Signature of Stacking Faults in 6H-SiC Epilayers Grown on Low Angle Off-axis Substrates
- 2012
-
Konferensbidrag (refereegranskat)abstract
- The radiative recombination spectra of 6H-SiC epilayers grown on low angle (1.4° off-axis) substrates have been investigated by low temperature photoluminescence spectroscopy. Four different types of stacking faults have been identified, together with the presence of 3C-SiC inclusions. From the energy of the momentum-conserving phonons, four excitonic band gap energies have been found with Egx equal to 2.837, 2.698, 2.600 and 2.525 eV. These photoluminescence features, which give a rapid and non-destructive approach to identify stacking faults in 6H-SiC, provide a direct feedback to improve the material growth.
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| 13. |
- Sun, Jianwu, et al.
(författare)
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Room temperature luminescence properties of fluorescent SiC as white light emitting diode medium
- 2012
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 522, s. 33-35
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Tidskriftsartikel (refereegranskat)abstract
- The high quantum efficiency of donor–acceptor-pair emission in N and B co-doped 6H–SiC opens the way for SiC to constitute as an efficient light-emitting medium for white light-emitting diodes. In this work, we evidence room temperature luminescence in N and B co-doped 6H–SiC fluorescent material grown by the Fast Sublimation Growth Process. Three series of samples, with eight different N and B doping levels, were investigated. In most samples, from photoluminescence measurements a strong N–B donor–acceptor-pair emission band was observed at room temperature, with intensity dependent on the nitrogen pressure in the growth chamber and boron doping level in the source. Low temperature photoluminescence spectra showed that N bound exciton peaks exhibited a continuous broadening with increasing N2 pressure during the growth, unambiguously indicating an opportunity to control the N doping in the epilayer by conveniently changing the N2 pressure. Finally, the crystal quality of the N and B doped 6H–SiC was evaluated by X-ray diffraction measurements. The ω rocking curves of (0006) Bragg diffractions from the samples grown with lower and higher N2 pressure show almost the same value of the full width at half maximum as that collected from the substrate. This suggests that the N and B doping, which is expected to give rise to an efficient donor–acceptor-pair emission at room temperature, does not degrade the crystal quality.
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| 14. |
- Sun, Jianwu, et al.
(författare)
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Shockley-Frank stacking faults in 6H-SiC
- 2012
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Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 111, s. 113527-
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Tidskriftsartikel (refereegranskat)abstract
- We report on Shockley-Frank stacking faults (SFs) identified in 6H-SiC by a combination of low temperature photoluminescence (LTPL) and high resolution transmission electron microscopy (TEM). In the faulted area, stacking faults manifested as large photoluminescence emissions bands located in between the 6H-SiC signal (at ∼2.99 eV) and the 3C-SiC bulk-like one (at ∼2.39 eV). Each of the stacking fault related emission band had a four-fold structure coming from the TA, LA, TO, and LO phonon modes of 3C-SiC. Up to four different faults, with four different thickness of the 3C-SiC lamella, could be observed simultaneously within the extent of the laser excitation spot. From the energy of the momentum-conservative phonons, they were associated with excitonic energy gaps at Egx1 = 2.837 eV, Egx2 = 2.689 eV, Egx3 = 2.600 eV and Egx4 = 2.525 eV. In the same part where low temperature photoluminescence was performed, high resolution transmission electron microscopy measurements revealed stacking faults which, in terms of the Zhdanov notation, could be recognized as SFs (3, 4), (3, 5), (3, 6), (3, 7), (3, 9), (3, 11), (3, 16) and (3, 22), respectively. Among them stacking fault (3, 4) was the most common one, but a faulted region with a (4, 4) 8H-SiC like sequence was also found. Using a type II 6H/3C/6H quantum-well model and comparing with experimental results, we find that the photoluminescence emissions with excitonic band gaps at 2.837 eV (Egx1), 2.689 eV (Egx2), 2.600 eV (Egx3) and 2.525 eV (Egx4) come from SFs (3, 4), (3, 5), (3, 6) and (3, 7), respectively. A possible formation mechanism of these SFs is suggested, which involves a combination of Frank faults with Shockley ones. This provides a basic understanding of stacking faults in 6H-SiC and gives a rapid and non-destructive approach to identify SFs by low temperature photoluminescence.
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| 15. |
- Sun, Jianwu, et al.
(författare)
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Splitting of type-I (N-B, P-Al) and type-II (N-Al, N-Ga) donor-acceptor pair spectra in 3C-SiC
- 2011
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Ingår i: PHYSICAL REVIEW B. - : American Physical Society. - 1098-0121. ; 83:19-15
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Tidskriftsartikel (refereegranskat)abstract
- Discrete series of lines have been observed for many years in donor-acceptor pair (DAP) spectra in 3C-SiC. In this work, the splitting of both type-I (N-B, P-Al) and type-II (N-Al, N-Ga) DAP spectra in 3C-SiC has been systematically investigated by considering the multipole terms. For type-I spectra, in which either N or B substitutes on C sites or P and Al replace Si, the splitting energy of the substructure for a given shell is almost the same for both pairs. For type-II spectra, in which N is on the C site while Al and Ga acceptors replace Si, we find that, when compared with literature data, the splitting energy for a given shell is almost independent of the identity of the acceptor. For both type-I and type-II spectra, this splitting energy can be successfully explained by the octupole term V-3 alone with k(3)=-2x10(5) angstrom(4) meV. Comparing the experimental donor and acceptor binding energies with the values calculated by the effective-mass model, this suggests that the shallow donor (N, P) ions can be treated as point charges while the charge distribution of the acceptor ions (Al, Ga, B) is distorted in accord with the T-d point group symmetry, resulting in a considerable value for k(3). This gives a reasonable explanation for the observed splitting energies for both type-I and type-II DAP spectra.
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| 16. |
- Sun, Jianwu W., et al.
(författare)
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Comparative micro-photoluminescence investigation of ZnO hexagonal nanopillars and the seeding layer grown on 4H-SiC
- 2012
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Ingår i: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 132:1, s. 122-127
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Tidskriftsartikel (refereegranskat)abstract
- We report on a comparative micro-photoluminescence investigation of ZnO hexagonal nanopillars (HNPs) and the seeding layer grown on the off-axis 4H-SiC substrate. Transmission electron microscope (TEM) results establish that a thin seeding layer continuously covers the terraces of 4H-SiC prior to the growth of ZnO HNPs. Low temperature photoluminescence (LTPL) shows that ZnO HNPs are only dominated by strong donor bound exciton emissions without any deep level emissions. Micro-LTPL mapping demonstrates that this is specific also for the seeding layer. To further understand the recombination mechanisms, time-resolved micro-PL spectra (micro-TRPL) have been collected at 5 K and identical bi-exponential decays have been found on both the HNPs and seeding layer. Temperature-dependent TRPL indicates that the decay time of donor bound exciton is mainly determined by the contributions of non-radiative recombinations. This could be explained by the TEM observation of the non-radiative defects in both the seeding layer and HNPs, like domain boundaries and dislocations, generated at the ZnO/SiC interface due to biaxial strain.
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| 17. |
- Zoulis, Georgios, et al.
(författare)
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Investigation of Low Doped n-Type and p-Type 3C-SiC Layers Grown on 6H-SiC Substrates by Sublimation Epitaxy
- 2010
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Ingår i: Silicon Carbide and Related Materials 2009. ; , s. 179-182
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Konferensbidrag (refereegranskat)abstract
- Both, n-type and p-type 3C-SiC samples grown on 6H-SiC substrates by sublimation epitaxy have been investigated. From low temperature photoluminescence studies, we demonstrate a low level of residual (n and/or p-type) doping with weak compensation, which is confirmed by secondary ion mass spectroscopy in the case of p-type samples.
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