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CVD growth of SiC for high-power and high-frequency applications
Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon Carbide (SiC) is a wide bandgap semiconductor that has attracted a lot of interest for electronic applications due to its high thermal conductivity, high saturation electron drift velocity and high critical electric field strength. In recent years commercial SiC devices have started to make their way into high and medium voltage applications.

Despite the advancements in SiC growth over the years, several issues remain. One of these issues is that the bulk grown SiC wafers are not suitable for electronic applications due to the high background doping and high density of basal plane dislocations (BPD). Due to these problems SiC for electronic devices must be grown by homoepitaxy. The epitaxial growth is performed in chemical vapor deposition (CVD) reactors. In this work, growth has been performed in a horizontal hot-wall CVD (HWCVD) reactor. In these reactors it is possible to produce high-quality SiC epitaxial layers within a wide range of doping, both n- and p-type.

SiC is a well-known example of polytypism, where the different polytypes exist as different stacking sequences of the Si-C bilayers. Polytypism makes polytype stability a problem during growth of SiC. To maintain polytype stability during homoepitaxy of the hexagonal polytypes the substrates are usually cut so that the angle between the surface normal and the c-axis is a few degrees, typically 4 or 8°. The off-cut creates a high density of micro-steps at the surface. These steps allow for the replication of the substrates polytype into the growing epitaxial layer, the growth will take place in a step-flow manner. However, there are some drawbacks with step-flow growth. One is that BPDs can replicate from the substrate into the epitaxial layer. Another problem is that 4H-SiC is often used as a substrate for growth of GaN epitaxial layers. The epitaxial growth of GaN has been developed on on-axis substrates (surface normal coincides with c-axis), so epitaxial 4H-SiC layers grown on off-axis substrates cannot be used as substrates for GaN epitaxial growth.

In efforts to solve the problems with off-axis homoepitaxy of 4H-SiC, on-axis homoepitaxy has been developed. In this work, further development of wafer-scale on-axis homoepitaxy has been made. This development has been made on a Si-face of 4H-SiC substrates. The advances include highly resistive epilayers grown on on-axis substrates. In this thesis the ability to control the surface morphology of epitaxial layers grown on on-axis homoepitaxy is demonstrated. This work also includes growth of isotopically enriched 4H-SiC on on-axis substrates, this has been done to increase the thermal conductivity of the grown epitaxial layers.

In (paper 1) on-axis homoepitaxy of 4H-SiC has been developed on 100 mm diameter substrates. This paper also contains comparisons between different precursors. In (paper 2) we have further developed on-axis homoepitaxy on 100 mm diameter wafers, by doping the epitaxial layers with vanadium. The vanadium doping of the epitaxial layers makes the layers highly resistive and thus suitable to use as a substrate for III-nitride growth. In (paper 3) we developed a method to control the surface morphology and reduce the as-grown surface roughness in samples grown on on-axis substrates. In (paper 4) we have increased the thermal conductivity of 4H-SiC epitaxial layers by growing the layers using isotopically enriched precursors. In (paper 5) we have investigated the role chlorine have in homoepitaxial growth of 4H-SiC. In (paper 6) we have investigated the charge carrier lifetime in as-grown samples and traced variations in lifetime to structural defects in the substrate. In (paper 7) we have investigated the formation mechanism of a morphological defect in homoepitaxial grown 4H-SiC.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. , p. 40
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1973
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-154467DOI: 10.3384/diss.diva-154467ISBN: 9789176851494 (print)OAI: oai:DiVA.org:liu-154467DiVA, id: diva2:1288642
Public defence
2019-02-27, Planck, Fysikhuset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2019-02-14 Created: 2019-02-14 Last updated: 2019-02-14Bibliographically approved
List of papers
1. The Role of Chlorine during High Growth Rate Epitaxy
Open this publication in new window or tab >>The Role of Chlorine during High Growth Rate Epitaxy
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2015 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 821-823, p. 141-144Article in journal (Refereed) Published
Abstract [en]

The influence of chlorine has been investigated for high growth rates of 4H-SiC epilayers on 4o off-cut substrates. Samples were grown at a growth rate of approximately 50 and 100 μm/h and various Cl/Si ratios. The growth rate, net doping concentration and charge carrier lifetime have been studied as a function of Cl/Si ratio. This study shows some indications that a high Cl concentration in the growth cell leads to less availability of Si during the growth process.

Place, publisher, year, edition, pages
Pfaffikon, Switzerland: Scientific.Net, 2015
Keywords
Chemical Vapor Deposition (CVD), Chlorine, Doping, Epitaxy, High Growth Rate
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-123951 (URN)10.4028/www.scientific.net/MSF.821-823.141 (DOI)
Conference
European Conference on Silicon Carbide & Related Materials, Grenoble, France, 21-25 September 2014
Available from: 2016-01-14 Created: 2016-01-14 Last updated: 2019-02-14Bibliographically approved
2. Long Charge Carrier Lifetime in As-Grown 4H-SiC Epilayer
Open this publication in new window or tab >>Long Charge Carrier Lifetime in As-Grown 4H-SiC Epilayer
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2016 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 858, p. 125-128Article in journal (Refereed) Published
Abstract [en]

Over 150 μm thick epilayers of 4H-SiC with long carrier lifetime have been grown with a chlorinated growth process. The carrier lifetime have been determined by time resolved photoluminescence (TRPL), the lifetime varies a lot between different areas of the sample. This study investigates the origins of lifetime variations in different regions using deep level transient spectroscopy (DLTS), low temperature photoluminescence (LTPL) and a combination of KOH etching and optical microscopy. From optical microscope images it is shown that the area with the shortest carrier lifetime corresponds to an area with high density of structural defects.

Place, publisher, year, edition, pages
Trans Tech Publications, 2016
Keywords
Carrier Lifetime, Chemical Vapor Deposition (CVD), Chlorine, Epitaxy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-154468 (URN)10.4028/www.scientific.net/MSF.858.125 (DOI)2-s2.0-84971500767 (Scopus ID)
Available from: 2019-02-13 Created: 2019-02-13 Last updated: 2019-02-21Bibliographically approved

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Karhu, Robin

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