| 51. |
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| 52. |
- Jokubavicius, Valdas, et al.
(författare)
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On stabilization of 3C-SiC using low off-axis 6H-SiC substrates
- 2012
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Konferensbidrag (refereegranskat)abstract
- Heteroepitaxial growth of 3C-SiC on 0.8 and 1.2 degree off-oriented 6H-SiC substrates was studied using a sublimation growth process. The 3C-SiC layers were grown at high growth rates with layer thickness up to 300 µm. The formation and the quality of 3C-SiC are influenced by the off-orientation of the substrate, the growth temperature (studied temperature range from 1750 oC to 1850oC), and the growth ambient (vacuum at 5*10-5 mbar and nitrogen at 5*10-1 mbar). The largest domains of 3C-SiC and the lowest number of double positioning boundaries were grown using nitrogen ambient and the highest growth temperature. The combined use of low off-axis substrate and high growth rate is a potential method to obtain material with bulk properties.
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| 53. |
- Jokubavicius, Valdas, 1983-, et al.
(författare)
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Silicon Carbide Surface Cleaning and Etching
- 2018
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Ingår i: Advancing Silicon Carbide Electronics Technology I. - : Materials Research Forum LLC. - 9781945291845 - 9781945291852 ; , s. 1-26
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Bokkapitel (refereegranskat)abstract
- Silicon carbide (SiC) surface cleaning and etching (wet, electrochemical, thermal) are important technological processes in preparation of SiC wafers for crystal growth, defect analysis or device processing. While removal of organic, particulate and metallic contaminants by chemical cleaning is a routine process in research and industrial production, the etching which, in addition to structural defects analysis, can also be used to modify wafer surface structure, is very interesting for development of innovative device concepts. In this book chapter we review SiC chemical cleaning and etching procedures and present perspectives of SiC etching for new device development.
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| 54. |
- Jokubavicius, Valdas, et al.
(författare)
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Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates
- 2015
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 15:6, s. 2940-2947
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the formation of structural defects in thick (∼1 mm) cubic silicon carbide (3C-SiC) layers grown on off-oriented 4H-SiC substrates via a lateral enlargement mechanism using different growth conditions. A two-step growth process based on this technique was developed, which provides a trade-off between the growth rate and the number of defects in the 3C-SiC layers. Moreover, we demonstrated that the two-step growth process combined with a geometrically controlled lateral enlargement mechanism allows the formation of a single 3C-SiC domain which enlarges and completely covers the substrate surface. High crystalline quality of the grown 3C-SiC layers is confirmed using high resolution X-ray diffraction and low temperature photoluminescence measurements.
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| 55. |
- Jokubavicius, Valdas, et al.
(författare)
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Stability in growth of 6H-SiC and 3C-SiC for LEDs and solar cells
- 2012
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Ingår i: 2012 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO). - : IEEE. - 9781557529435
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Konferensbidrag (refereegranskat)abstract
- 6H- and 3C-SiC layers were grown using a sublimation based process. The polytype balance is mainly given by the substrate orientation and growth temperature. This paves the way to use 6H- and 3C-SiC in optoelectronic applications.
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| 56. |
- Jokubavičius, Valdas
(författare)
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Sublimation Growth of 3C-SiC : From Thick Layers to Bulk Material
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon carbide (SiC) is a semiconductor material which holds high promises for various device applications. It can be obtained in different crystal structures called polytypes. The most common ones are hexagonal (6H- and 4H-SiC) and cubic (3C-SiC) silicon carbide. The 6H- and 4H-SiC single crystal substrates are commercially available, while technologies for the growth of 3C-SiC are still under development. The unique 3C-SiC properties like isotropy, narrower bandgap (2.4 eV) compared to hexagonal polytypes (about 3 eV) and high electron mobility make it better over hexagonal counterparts for some semiconductor applications, for example, metal oxide semiconductor field effect transistors (MOSFETs). However, due to lack of high quality material, the full potential of 3C-SiC in device applications has not been revealed. In addition, it has properties suitable to explore new concepts in efficient photovoltaics or solar driven hydrogen generation by water splitting.There is a need for 3C-SiC seeds to grow large 3C-SiC crystals by the widely used Physical Vapor Transport (PVT) technique. In case of hexagonal SiC polytypes such seeds were produced by the Lely method during which hexagonal SiC crystals spontaneously nucleate on the inner walls of a crucible. However, the formation of 3C-SiC using the Lely method is rarely observed. Therefore, the 3C-SiC has to be heteroepitaxially grown on silicon or hexagonal SiC substrates. Silicon is an inexpensive material with very high crystalline quality. However, due to almost 20% mismatch in lattice parameters and 8% difference in thermal expansion coefficient there is a high density of structural defects formed at the 3C-SiC/Si interface. In contrast, the 3C-SiC/hexagonal SiC material system does not encounter such problems, but there are other challenges like polytype stability or formation of structural defects called double positioning boundaries (DPBs).This thesis work mainly focuses on the growth of 3C-SiC on hexagonal SiC substrates using sublimation epitaxy. The research covers the development of growth process for thick (~1 mm) 3C-SiC layers, advancement of the growth process to eliminate DPBs and growth of bulk material using thick 3C-SiC layers as seeds. The 3C-SiC was grown on off-oriented hexagonal SiC substrates. The surfaces of such substrates contain high density of steps. Therefore, they have mostly been used for the growth of homoepitaxial hexagonal layers or bulk crystals via step flow mechanism. However, as demonstrated in this thesis, under special conditions the 3C-SiC with high crystalline quality can also be grown on off-oriented hexagonal substrates. The stability window for the growth of hexagonal and cubic polytypes on nominally on-axis hexagonal SiC substrates is also explored. Moreover, it is demonstrated how the temperature profile inside the graphite crucible is influenced by the change in thermal insulation properties and how such change results in enhanced polytype stability during the growth of thick SiC layers. In addition, different sources for sublimation epitaxial growth of doped SiC layers were analyzed to gain further understanding of new parameter windows.As a part of this thesis, a sublimation etching of 6H-, 4H- and 3C-SiC polytypes is presented using two different etching arrangements in vacuum (10-5 mbar) and Ar ambient. It is demonstrated that this technique can be used to remove residual scratches on the surface as well as to obtain various surface step structures which could be used for the growth of graphene nanostructures.
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| 57. |
- Jokubavicius, Valdas, et al.
(författare)
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Surface engineering of SiC via sublimation etching
- 2016
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Ingår i: Applied Surface Science. - Amsterdam : Elsevier BV. - 0169-4332 .- 1873-5584. ; 390, s. 816-822
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Tidskriftsartikel (refereegranskat)abstract
- We present a technique for etching of SiC which is based on sublimation and can be used to modify the morphology and reconstruction of silicon carbide surface for subsequent epitaxial growth of various materials, for example graphene. The sublimation etching of 6H-, 4H- and 3C-SiC was explored in vacuum (10−5 mbar) and Ar (700 mbar) ambient using two different etching arrangements which can be considered as Si-C and Si-C-Ta chemical systems exhibiting different vapor phase stoichiometry at a given temperature. The surfaces of different polytypes etched under similar conditions are compared and the etching mechanism is discussed with an emphasis on the role of tantalum as a carbon getter. To demonstrate applicability of such etching process graphene nanoribbons were grown on a 4H-SiC surface that was pre-patterned using the thermal etching technique presented in this study.
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| 58. |
- Jokubavicius, Valdas, et al.
(författare)
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Towards bulk-like 3C-SiC growth using low off-axis substrates
- 2013
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2012. - : Trans Tech Publications. ; , s. 275-278
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Konferensbidrag (refereegranskat)abstract
- Bulk-like 3C-SiC was grown on 1.2 degrees low off-axis 6H-SiC substrates using a sublimation epitaxy technique. The effects of temperature ramp-up and increase in layer thickness on the 3C-SiC domain formation were explored. The temperature ramp-up had no significant effect on the domain size. The domain size was considerably increased and the crystal quality was significantly improved by increasing the thickness of the layer towards bulk-like material. Average full width at half maximum values of 149 arcsec and 65 arcsec were measured in samples with thicknesses of 305 mu m and 1080 mu m, respectively, at a footprint of 1x3 mm(2). This result implies that heteropeitaxial growth of 3C-SiC on low off-axis 6H-SiC substrates by a sublimation method can be used to prepare 3C-SiC seeds or can be further developed for growth of bulk 3C-SiC material.
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| 59. |
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| 60. |
- Kaiser, M., et al.
(författare)
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Nucleation and growth of polycrystalline SiC
- 2014
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Ingår i: IOP Conference Series. - : Institute of Physics Publishing (IOPP). ; 56:1, s. 012001-
-
Konferensbidrag (refereegranskat)abstract
- The nucleation and bulk growth of polycrystalline SiC in a 2 inch PVT setup using isostatic and pyrolytic graphite as substrates was studied. Textured nucleation occurs under near-thermal equilibrium conditions at the initial growth stage with hexagonal platelet shaped crystallites of 4H, 6H and 15R polytypes. It is found that pyrolytic graphite results in enhanced texturing of the nucleating gas species. Reducing the pressure leads to growth of the crystallites until a closed polycrystalline SiC layer containing voids with a rough surface is developed. Bulk growth was conducted at 35 mbar Ar pressure at 2250°C in diffusion limited mass transport regime generating a convex shaped growth form of the solid-gas interface leading to lateral expansion of virtually [001] oriented crystallites. Growth at 2350°C led to the stabilization of 6H polytypic grains. The micropipe density in the bulk strongly depends on the substrate used.
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