| 1. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
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Structural properties of 6H-SiC epilayers grown by two different techniques
- 1997
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Ingår i: Materials Science and Engineering B. - 0921-5107. ; 46:1-3, s. 345-348
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Tidskriftsartikel (refereegranskat)abstract
- In the present work we investigated the structural properties of 6H-SiC homoepitaxial layers utilizing microhardness and X-ray characterization techniques. The growth was performed by chemical vapour deposition (CVD) and liquid phase epitaxy (LPE) under various growth conditions. The depth Knoop hardness profiles represent decreasing curves due to the indentation size effect. With load increasing the curves saturate reaching microhardness values comparable with the known Vickers ones. At about 0.4 μm beneath the layer surfaces the curves show small plateaus which may be attributed to structural inhomogeneity. This is suggested by X-ray diffraction spectra taken from the same samples, which contain additional peaks besides the typical ones for 6H-SiC.
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| 2. |
- Pecz, B, et al.
(författare)
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Structural investigation of SiC epitaxial layers grown under microgravity and on-ground conditions
- 1999
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 357:2, s. 137-143
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Tidskriftsartikel (refereegranskat)abstract
- Thick 4H-, and 6H-SiC epitaxial layers have been grown by LPE from Si-Sc-C solvent at microgravity conditions during a space experiment, as well as on-ground. The samples are characterised by cross-sectional TEM and HRXRD. Layers grown at microgravity are relatively defect free, although their surfaces are always stepped. Control samples grown on-ground have similar surface appearance, but contain scandium carbide precipitates, nanopipes, micropipes and/or cavities as verified by TEM. However, none of the aforementioned defects was traced in the layers grown at microgravity conditions. So, samples grown at space microgravity conditions are superior in their defect structure to those ones grown on the ground. The defects called nanopipes can be described as empty pipes of about 200 nm diameter traversing the layer in the [0001] (growth) direction. The steps in the microgravity and on-ground samples have facets of {104} type crystallographic planes both in 6H-, and 4H-SiC. We suggest, that those facets are formed and preferred during growth due to a possible mechanism of decreasing the high energy of the growing Si terminated (0001) surface. (C) 1999 Elsevier Science S.A. All rights reserved.
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| 3. |
- Pecz, B, et al.
(författare)
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Structure of SiC layers grown by LPE in microgravity and on-ground conditions
- 1999
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Ingår i: Institute of Physics Conference Series. - 0951-3248 .- 2154-6630. ; :164, s. 243-246
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Tidskriftsartikel (refereegranskat)abstract
- High quality, hexagonal SiC layers have been grown in microgravity conditions and on-ground as well. The surface of the layers is always stepped. The dislocation density of the layers is increased closer to the surface. Scandium carbide precipitates, nanopipes and cavities were found in the SiC layers grown on-ground, but none of them were traced in the layers grown under microgravity conditions.
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| 4. |
- Syväjärvi, Mikael, et al.
(författare)
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Anisotropy of dissolution and defect revealing on SiC surfaces
- 1999
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 11:49, s. 10041-10046
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Tidskriftsartikel (refereegranskat)abstract
- Micropipes and dislocations in silicon carbide single crystals are revealed by chemical etching. Micropipes are shown to be interconnected with other structural defects and the reason for this is discussed. The Si and C faces are attacked by molten KOH preferentially and isotropically, respectively. The mechanism is discussed in relation to the different surface free energies on the Si and C faces. The revealing of micropipes is more pronounced on the Si face. The hexagonal pattern of micropipes are revealed by rapid etching provided by a large undersaturation at the surface. It is shown that etching from a melt gives a disintegration of the SiC crystal at the micropipe via spiral dissolution which is due to etching near equilibrium conditions. The temperature dependence of the etch rate follows an Arrhenius dependence with an apparent activation energy of about 12-15 kcal mol(-1) derived from measuring etch rate and weight loss.
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| 5. |
- Syväjärvi, Mikael, et al.
(författare)
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Growth of 6H and 4H-SiC by sublimation epitaxy
- 1999
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 197:1-2, s. 155-162
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Tidskriftsartikel (refereegranskat)abstract
- The epitaxial sublimation growth process of SiC has been investigated. Layers with specular surfaces and growth rates up to 2 mm/h have been obtained. No step bunching is observed by optical microscopy even on very thick layers which indicates a stable step growth mechanism. Under certain growth conditions the morphology degrades. The morphological stability is investigated and discussed in relation to the growth kinetics. Impurities in the epitaxial layers are investigated by secondary ion mass spectroscopy and low-temperature photoluminescence. The carrier concentration is measured by capacitance–voltage measurements. The structural quality of the grown material is improved compared to the substrate as shown by X-ray diffraction measurements.
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| 6. |
- Syväjärvi, Mikael, 1968-
(författare)
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High growth rate epitaxy of SiC: growth processes and structural quality
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon carbide (SiC) is a promising wide-bandgap semiconductor for applications such as high-power devices, high-voltage switches, high-temperature electronics and microwave components. The prospect of using this material is a large driving force for improving the material growth which is still quite immature in comparison with established semiconductor materials (e.g. silicon). There is an increasing number of reports in growth of large area boules and epilayers, but the fundamental growth issues are often not discussed (or not known) which holds back the advancement in the growth technology.Chemical vapor deposition (CVD) is the technique which has achieved epitaxial layers with low residual doping (<1015cm-3) and smooth surface morphology, two requirements for device quality material. The drawback of CVD is the low growth rate (<5 μm/hr). Since material cost is one limitation for industrial applications, increased growth rates would be preferred.Two epitaxial techniques which yield high growth rates (several tens or hundreds of μm/hr) are liquid phase epitaxy and sublimation epitaxy, both of which have been investigated within the present work. The first method is appealing since growth from the liquid phase is a growth technique under near equilibrium conditions thus providing a base for growth of high-quality material. In paper I a SiC liquid phase epitaxy technique is described. The growth process and the quality of the grown material are investigated to gain understanding of this high growth rate technique. Several factors affect the quality of the grown material. One important parameter is the quality of the interface at the growing crystal surface. This is studied in paper II for liquid phase growth where the SiC/solvent interfacial properties are investigated. The results are used for estimating the surface free energy of 4H-SiC. In liquid phase epitaxy the influence of gravity induced convection is more pronounced than in vapor phase growth. This effect was studied in paper III where comparisons in growth rate, doping incorporation and structural quality of layers grown on-ground and for the first time for SiC layers grown under microgravity conditions were made.In liquid phase epitaxy with high growth rates, a smooth surface morphology is difficult to achieve due to increased step heights (up to 1 μm) caused by pronounced stepbunching. For further understanding of SiC epitaxial growth with high growth rates, the sublimation epitaxy growth technique was studied in paper IV. It is shown that growth rates up to 2 mm/hr are achieved and the surface is smooth without observation of macrosteps using optical microscopy. The limitations in growth conditions for morphological stable growth are investigated for 6H and 4H-SiC. Studies of the kinetics show that the growth rate limiting process is sublimation of the SiC source material.Defects are often observed on as-grown surfaces but for deeper understanding of the formation mechanisms involved, cross-sections of epitaxial layers are important to study. Application of cross-sectional cleavages for investigating SiC epitaxial layers has been investigated in paper V. The preferred cleavage planes are related to the crystal structure of SiC. Appearance of defects and other polytypes than given by the substrate is a difficult matter in the growth process. Fundamentals in formation of these imperfections have been investigated in paper VI for growth using on-axis and offoriented substrates. These issues are more crucial in bulk growth where improper growth behaviour may lead to morphologically unstable growth and a phase transition from 4H-SiC polytype to 6H-SiC during the first millimeters of growth. The initial stages of crystal formation in seeded sublimation bulk growth are studied in paper VII and single 4H-SiC boules without polytype conversion were grown.The structural quality of the grown material is a fundamental property in growth. In paper VIII structural improvement, as compared with the substrates used, is demonstrated for sublimation epitaxy. Different misoriented domains in the substrate merge into one with one major orientation. A mechanism for this process is proposed. The as-grown surfaces are free of morphological defects which typically appear in SiC epitaxy. It is also shown that the improvement in structural quality is maintained when growth is performed on substrates containing a layer grown by liquid phase epitaxy. This is a technique for reducing micropipe densities in the substrates. Even though starting from a LPE layer surface showing steps, smooth surfaces were achieved using sublimation epitaxy. This finding may have an important practical impact.
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| 7. |
- Syväjärvi, Mikael, et al.
(författare)
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Kinetics and morphological stability in sublimation growth of 6H and 4H-SiC epitaxial layers
- 1999
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Ingår i: Materials Science and Engineering: B. - 0921-5107. ; 61-62, s. 161-164
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Tidskriftsartikel (refereegranskat)abstract
- Very high growth rates (>2 mm h−1) in SiC epitaxy have been achieved. The rate determining mechanism changes from diffusion to kinetics when the growth pressure decreases below 5–10 mbar. At low pressures it is shown that sublimation of the SiC source is the rate determining step and that there is a free molecular transport from source to substrate. The growth rate is constant during several hours of growth and Si losses from the crucible are very small. These facts show that our growth system is stable. The obtained apparent activation energy (130 kcal mol−1) is attributed to the sublimation rate of the SiC source material. The morphology is smooth and the surfaces are specular if the growth conditions are selected within the given parameter window for morphological stability. The origin of the growth disturbances is discussed.
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| 8. |
- Syväjärvi, Mikael, et al.
(författare)
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Step-bunching in 6H-SiC growth by sublimation epitaxy
- 1999
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 11:49, s. 10019-10024
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Tidskriftsartikel (refereegranskat)abstract
- Thick 6H-SiC epitaxial layers grown by sublimation epitaxy have been investigated concerning step-bunching. The macrostep appearances on the surfaces were studied for both (0001) Si and (000 (1) over bar) C faces. The surface structure on the Si face is less regular compared with the C face. Data on the steps have been collected and the step height shows a linear relation with the step width.
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| 9. |
- Tuominen, M., et al.
(författare)
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Investigation of domain evolution in sublimation epitaxy of SiC
- 1998
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 193:1-2, s. 101-108
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Tidskriftsartikel (refereegranskat)abstract
- High resolution X-ray diffractometry has been applied to study domain misorientation in SiC epi-layers grown by the sublimation epitaxy method. A pronounced effect of the growth conditions on the mosaicity of the epi-layer has been observed. The results are discussed in terms of domain evolution and structural changes during the epi-growth under different growth conditions.
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