| 1. |
- Booker, Ian Don, et al.
(författare)
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Shallow boron, the deep D-center and their influence on carrier lifetime in n- and p-type 4H-SiC
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The shallow boron and deep D-center are analyzed by minority carrier transient spectroscopy (MCTS), deep level transient spectroscopy (DLTS) and optical-electrical MCTS in n-type 4H-SiC with varying concentrations of boron, and in p-type 4H-SiC. MCTS, using high resolution correlation functions, shows the D-center to be composed of two closely overlapping peaks, referred to as D(a) and D(b), both most likely originating from the same defect located on inequivalent lattice sites. The hole capture cross sections of the D center are derived from DLTS filling pulse measurements in p-type material. The electron capture behavior of the D-center is analyzed by optical-electrical MCTS, and we find the center to be a pure hole trap, unable to act as a recombination center, with electron capture cross sections smaller than 1·10-23 cm2. The shallow boron peak is found to be composed of two or more overlapping levels in high resolution MCTS spectra. The shallow levels are further demonstrated to produce minority carrier trapping and detrapping effects in n-type 4H-SiC, which result in long time-resolved photoluminescence (TRPL) transients with microsecond decay constants, even in material containing high concentrations of the lifetime killing center Z1/2.
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| 2. |
- Danielsson, Örjan, et al.
(författare)
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Simulation of Gas-Phase Chemistry for Selected Carbon Precursors in Epitaxial Growth of SiC
- 2013
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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 740-742, s. 213-216
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Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations are one way to obtain a better and more detailed understanding of the chemical vapor deposition process of silicon carbide. Although several attempts have been made in this area during the past ten years, there is still no general model valid for any range of process parameters and choice of precursors, that can be used to control the growth process, and to optimize growth equipment design. In this paper a first step towards such a model is taken. Here, mainly the hydrocarbon chemistry is studied by a detailed gas-phase reaction model, and comparison is made between C3H8 and CH4 as carbon precursor. The results indicate that experimental differences, which previous models have been unable to predict, may be explained by the new model.
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| 3. |
- Ivanov, Ivan Gueorguiev, et al.
(författare)
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High-Resolution Raman and Luminescence Spectroscopy of Isotope-Pure (SiC)-Si-28-C-12, Natural and C-13 - Enriched 4H-SIC
- 2014
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Ingår i: Silicon Carbide and Related Materials 2013, PTS 1 AND 2. - : Trans Tech Publications Inc.. ; , s. 471-474
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Konferensbidrag (refereegranskat)abstract
- The optical properties of isotope-pure (SiC)-Si-28-C-12, natural SiC and enriched with C-13 isotope samples of the 4H polytype are studied by means of Raman and photoluminescence spectroscopies. The phonon energies of the Raman active phonons at the Gamma point and the phonons at the M point of the Brillouin zone are experimentally determined. The excitonic bandgaps of the samples are accurately derived using tunable laser excitation and the phonon energies obtained from the photoluminescence spectra. Qualitative comparison with previously reported results on isotope-controlled Si is presented.
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| 4. |
- Lundqvist, Björn, et al.
(författare)
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Thermal conductivity of isotopically enriched silicon carbide
- 2013
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Ingår i: THERMINIC 2013 - 19th International Workshop on Thermal Investigations of ICs and Systems, Proceedings. - : IEEE. ; , s. 58-61, s. 58-61
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Konferensbidrag (refereegranskat)abstract
- Since the semiconductor silicon carbide presents attractive opportunities for the fabrication of novel electronic devices, there is significant interest in improving its material quality. Shrinking component sizes and high demands for efficiency and reliability make the capability to release excess heat an important factor for further development. Experience from Si and Diamond tells us that isotopic enrichment is a possible way to increase the thermal conductivity. We have produced samples of 4H-SiC that contain 28Si and 12C to a purity of 99.5%. The thermal conductivity in the c-direction of these samples has been measured by a transient thermoreflectance method. An improvement due to enrichment of at least 18% was found. The result is valid for a temperature of 45K above room temperature. A preliminary study of the temperature dependence of the thermal conductivity demonstrates a strong temperature dependence in agreement with earlier reports for 4H. © 2013 IEEE.
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| 5. |
- Yazdanfar, Milan, et al.
(författare)
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Brominated chemistry for chemical vapor deposition of electronic grade SiC
- 2015
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 27:3, s. 793-801
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Tidskriftsartikel (refereegranskat)abstract
- Chlorinated chemical vapor deposition (CVD) chemistry for growth of homoepitaxial layers of silicon carbide (SiC) has paved the way for very thick epitaxial layers in short deposition time as well as novel crystal growth processes for SiC. Here, we explore the possibility to also use a brominated chemistry for SiC CVD by using HBr as additive to the standard SiC CVD precursors. We find that brominated chemistry leads to the same high material quality and control of material properties during deposition as chlorinated chemistry and that the growth rate is on average 10 % higher for a brominated chemistry compared to chlorinated chemistry. Brominated and chlorinated SiC CVD also show very similar gas phase chemistries in thermochemical modelling. This study thus argues that brominated chemistry is a strong alternative for SiC CVD since the deposition rate can be increased with preserved material quality. The thermochemical modelling also suggest that the currently used chemical mechanism for halogenated SiC CVD might need to be revised.
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| 6. |
- Yazdanfar, Milan, et al.
(författare)
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Carrot defect control in chloride-based CVD through optimized ramp up conditions
- 2012
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Ingår i: Materials Science Forum Vols 717 - 720. - : Trans Tech Publications Inc.. ; , s. 109-112
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Konferensbidrag (refereegranskat)abstract
- Epitaxial growth of 4H-SiC on 8 degrees off-axis substrates has been performed under different condition during the temperature ramp up in order to study the effect on the carrot defect. The study was done in a hot wall chemical vapor deposition reactor using the single molecule precursor methyltrichlorosilane (MTS). During the temperature ramp up, a small flow of HCl or C2H4 was added to the H-2 ambient to study different surface etching conditions. The best result was obtained when HCl was added from 1175 to 1520 degrees C during the ramp up to growth temperature (1575 degrees C).
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| 7. |
- Yazdanfar, Milan, et al.
(författare)
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Effect of process parameters on dislocation density in thick 4H-SiC epitaxial layers grown by chloride-based CVD on 4 degrees off-axis substrates
- 2014
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2. - : Trans Tech Publications. ; , s. 159-162
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Konferensbidrag (refereegranskat)abstract
- The effect of process parameters such as growth temperature, C/Si ratio, etching time, and Si/H2 ratio on dislocation density was investigated by performing KOH etching on 100 mu m thick epitaxial layers grown on 4 degrees off axis 4H-SiC substrates at various growth conditions by a chemical vapor deposition (CVD) process using a chloride-based chemistry to achieve growth rates exceeding 100 mu m/h. We observe that the growth temperature and the growth rate have no significant influence on the dislocation density in the grown epitaxial layers. A low C/Si ratio increases the density of threading screw dislocations (TSD) markedly. The basal plane dislocation (BPD) density was reduced by using a proper in-situ etch prior to growth.
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| 8. |
- Yazdanfar, Milan, et al.
(författare)
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Finding the Optimum Chloride-Based Chemistry for Chemical Vapor Deposition of SiC
- 2014
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Ingår i: ECS Journal of Solid State Science and Technology. - : ECS. - 2162-8769 .- 2162-8777. ; 3:10, s. P320-P323
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Tidskriftsartikel (refereegranskat)abstract
- Chemical vapor deposition of silicon carbide with a chloride-based chemistry can be done using several different silicon and carbon precursors. Here, we present a comparative study of SiCl4, SiHCl3, SiH4+HCl, C3H8, C2H4 and CH4 in an attempt to find the optimal precursor combination. We find that while the chlorinated silanes SiCl4 and especially SiHCl3 give higher growth rate than natural silane and HCl, SiH4+HCl gives better morphology at C/Si around 1 and SiCl4 gives the best morphology at low C/Si. Our study shows no effect on doping incorporation with precursor chemistry. We suggest that these results can be explained by the number of reaction steps in the gas phase chemical reaction mechanisms for producing SiCl2, which is the most important Si species, and by formation of organosilicons in the gas phase. As carbon precursor, C3H8 or C2H4 are more or less equal in performance with a slight advantage for C3H8, CH4 is however not a carbon precursor that should be used unless extraordinary growth conditions are needed.
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| 9. |
- Yazdanfar, Milan, et al.
(författare)
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Morphology optimization of very thick 4H-SiC epitaxial layers
- 2013
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2012. - : Trans Tech Publications. ; , s. 251-254
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Konferensbidrag (refereegranskat)abstract
- Epitaxial growth of about 200 gm thick, low doped 4H-SiC layers grown on n-type 8 degrees off-axis Si-face substrates at growth rates around 100 mu m/h has been done in order to realize thick epitaxial layers with excellent morphology suitable for high power devices. The study was done in a hot wall chemical vapor deposition reactor without rotation. The growth of such thick layers required favorable pre-growth conditions and in-situ etch. The growth of 190 gm thick, low doped epitaxial layers with excellent morphology was possible when the C/Si ratio was below 0.9. A low C/Si ratio and a favorable in-situ etch are shown to be the key parameters to achieve 190 gm thick epitaxial layers with excellent morphology.
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| 10. |
- Yazdanfar, Milan, et al.
(författare)
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On the use of methane as a carbon precursor in Chemical Vapor Deposition of silicon carbide
- 2014
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 390, s. 24-29
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Tidskriftsartikel (refereegranskat)abstract
- It is generally considered that methane is not a suitable carbon precursor for growth of silicon carbide (SiC) epitaxial layers by Chemical Vapor Deposition (CVD) since its use renders epitaxial layers with very high surface roughness. In this work we demonstrate that in fact SiC epitaxial layers with high-quality morphology can be grown using methane. It is shown that a key factor in obtaining high-quality material is tuning the C/Si ratio of the process gas mixture to a region where the growth is limited neither by carbon nor by silicon supplies. From the growth characteristics presented here, we argue that the reactivity of methane with the SiC surface is much higher than generally assumed in SiC CVD modeling today.
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