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  • Disputation: 2019-02-27 13:15 Planck, Fysikhuset, Linköping
    Karhu, Robin
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    CVD growth of SiC for high-power and high-frequency applications2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

    Delarbeten
    1. The Role of Chlorine during High Growth Rate Epitaxy
    Öppna denna publikation i ny flik eller fönster >>The Role of Chlorine during High Growth Rate Epitaxy
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    2015 (Engelska)Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 821-823, s. 141-144Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Pfaffikon, Switzerland: Scientific.Net, 2015
    Nyckelord
    Chemical Vapor Deposition (CVD), Chlorine, Doping, Epitaxy, High Growth Rate
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-123951 (URN)10.4028/www.scientific.net/MSF.821-823.141 (DOI)
    Konferens
    European Conference on Silicon Carbide & Related Materials, Grenoble, France, 21-25 September 2014
    Tillgänglig från: 2016-01-14 Skapad: 2016-01-14 Senast uppdaterad: 2019-02-14Bibliografiskt granskad
    2. Long Charge Carrier Lifetime in As-Grown 4H-SiC Epilayer
    Öppna denna publikation i ny flik eller fönster >>Long Charge Carrier Lifetime in As-Grown 4H-SiC Epilayer
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    2016 (Engelska)Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 858, s. 125-128Artikel i tidskrift (Refereegranskat) 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.

    Ort, förlag, år, upplaga, sidor
    Trans Tech Publications, 2016
    Nyckelord
    Carrier Lifetime, Chemical Vapor Deposition (CVD), Chlorine, Epitaxy
    Nationell ämneskategori
    Den kondenserade materiens fysik
    Identifikatorer
    urn:nbn:se:liu:diva-154468 (URN)10.4028/www.scientific.net/MSF.858.125 (DOI)
    Tillgänglig från: 2019-02-13 Skapad: 2019-02-13 Senast uppdaterad: 2019-02-14
  • Disputation: 2019-03-01 13:00 I:101, Hus I, Linköping
    Halvarsson Lundkvist, Agneta
    Linköpings universitet, Institutionen för beteendevetenskap och lärande, Pedagogik och sociologi. Linköpings universitet, Filosofiska fakulteten.
    Learning Dynamics of Workplace Development Programmes: Studies in Swedish national programmes2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    I denna avhandling ligger fokus på tre nationella utvecklingsprogram vars avsikt är att stödja arbetsplatser och organisationer för att realisera beslutsfattares policyer. Med utgångspunkt från ett arbetsplatslärandeperspektiv är syftet med avhandlingen att bidra med kunskap om lärande i arbetsplatsutvecklingsprogram och organisationer som dessa stödjer för att realisera policyer för utveckling av arbetsplatser. Studien har en multipel fallstudiedesign och totalt 115 intervjuer och anteckningar från möten ingår i datamaterialet. Resultaten visar att kontinuerligt lärande mellan intressenter på olika nivåer i programmen var en nödvändig förutsättning när en policy skulle realiseras. Särskilt viktigt var att de som representerade intressenterna tog rollen som mäklare vilket krävde rätt kvalifikationer och karaktärer för att kunna knyta samman de olika intressenterna som realiserade policyn. Den övergripande slutsatsen är att dynamiken i realiserande av policyer av detta slag visar på orimligheten i att hitta en modell för lärande som passar alla arbetsplatsutvecklingsprogram. Vidare kan ett utvecklingsprogram skapa goda förutsättningar för lärande i deltagande organisationer om programmet ger stöd vid utformning av förändringsinsatsen och vid utveckling av en intern infrastruktur som fortsätter att stödja utveckling av arbetsplatsen efter det att programmet avslutas.  

    Delarbeten
    1. Program steering by learning
    Öppna denna publikation i ny flik eller fönster >>Program steering by learning
    2015 (Engelska)Ingår i: Sustainable development in organizations: studies on innovative practices / [ed] Mattias Elg, Per-Erik Ellström, Magnus Klofsten, Malin Tillmar, Cheltenham: Edward Elgar Publishing, 2015, s. 77-92Kapitel i bok, del av antologi (Refereegranskat)
    Ort, förlag, år, upplaga, sidor
    Cheltenham: Edward Elgar Publishing, 2015
    Nyckelord
    Organisationsförändringar
    Nationell ämneskategori
    Ekonomi och näringsliv
    Identifikatorer
    urn:nbn:se:liu:diva-125518 (URN)000374407200006 ()978-17-8471-688-2 (ISBN)
    Tillgänglig från: 2016-02-25 Skapad: 2016-02-25 Senast uppdaterad: 2019-02-13Bibliografiskt granskad
    2. The role of brokers in a workplace development programme targeting SMEs
    Öppna denna publikation i ny flik eller fönster >>The role of brokers in a workplace development programme targeting SMEs
    2018 (Engelska)Ingår i: European Journal of Training and Development, ISSN 2046-9012, E-ISSN 2046-9020Artikel i tidskrift (Refereegranskat) Epub ahead of print
    Abstract [en]

    Purpose

    The purpose of this paper is to investigate the development of a workplace development programme (WPDP) targeting small and medium sized manufacturing enterprises (SMEs) by focussing on the people who acted as brokers providing cross-boundary connections between its collaborating partners.

    Design/methodology/approach

    The material, from interviews with 32 individuals and 11 meetings, was analysed in a boundary-crossing framework, which provided tools to reveal how the roles of brokers at different levels (operative, strategic and national) of the WPDP affected its development.

    Findings

    The findings indicate that cross-boundary connections were made by persons who acted as brokers within and between different levels of the WPDP. The brokers who provided cross-boundary connections between different levels of the WPDP were found to play the most important role for the prompt development of the WPDP.

    Originality/value

    Apart from unique empirical material depicting the development of a collaborative venture between national and regional stakeholders of the manufacturing industry, the value of this study is the attention given to the people behind the policymaking of publicly funded national WPDPs, revealing the complex business of developing policy-driven competence development activities to employees in SMEs.

    Ort, förlag, år, upplaga, sidor
    Emerald Group Publishing Limited, 2018
    Nyckelord
    SME, Manufacturing industry, Programme development, Broker, Cross-boundary connections, Workplace development programme
    Nationell ämneskategori
    Lärande
    Identifikatorer
    urn:nbn:se:liu:diva-151603 (URN)10.1108/EJTD-04-2018-0037 (DOI)2-s2.0-85053333619 (Scopus ID)
    Tillgänglig från: 2018-09-27 Skapad: 2018-09-27 Senast uppdaterad: 2019-02-13Bibliografiskt granskad
    3. Learning conditions for continuous improvement in a public service organization
    Öppna denna publikation i ny flik eller fönster >>Learning conditions for continuous improvement in a public service organization
    2018 (Engelska)Ingår i: Journal of Workplace Learning, ISSN 1366-5626, E-ISSN 1758-7859Artikel i tidskrift (Refereegranskat) Epub ahead of print
    Abstract [en]

    Purpose – This study focuses on a transformation effort in a social welfare department of a Swedish municipality where continuous improvement, which is a Lean principle, was introduced in employees’everyday work via a workplace development programme (WPDP). The aim of this paper is to explore the conditions (internal and external) that enabled or constrained employee learning during the introduction of continuous improvement into employees’ everyday work in a WPDP-supported social welfare department.

    Design/methodology/approach – This case study is based mainly on 22 semi-structured interviews with individuals holding different positions in the department and overarching municipality.

    Findings – The findings show that multiple and emerging conditions, both internal and external, shaped a predominantly restrictive learning environment during the introduction of continuous improvement into the social welfare department. The major conditions identified were related to the initial implementation and top management’s steering and monitoring of the “Lean investment”, activities and support provided by the WPDP, activities and support provided by the internal Lean support team and first-line managers’ abilities to facilitate employee learning.

    Originality/value – Apart from unique empirical material depicting an effort towards change under conditions far from favourable for employee learning, the value of this study lies in the attention given to the external dynamics that drive change in line with the concept of new public management in public service organizations, including a WPDP that supported the social welfare department.

    Ort, förlag, år, upplaga, sidor
    Emerald Group Publishing Limited, 2018
    Nyckelord
    Organizational change, learning environment, public service organization, workplace development programmes
    Nationell ämneskategori
    Lärande
    Identifikatorer
    urn:nbn:se:liu:diva-152661 (URN)10.1108/JWL-03-2018-0049 (DOI)
    Tillgänglig från: 2018-11-12 Skapad: 2018-11-12 Senast uppdaterad: 2019-02-13Bibliografiskt granskad
    4. Conditions for Employee Learning and Innovation: Interweaving Competence Development Activities Provided by a Workplace Development Programme with Everyday Work Activities in SMEs
    Öppna denna publikation i ny flik eller fönster >>Conditions for Employee Learning and Innovation: Interweaving Competence Development Activities Provided by a Workplace Development Programme with Everyday Work Activities in SMEs
    2018 (Engelska)Ingår i: Vocations and Learning, ISSN 1874-785X, E-ISSN 1874-7868, Vol. 11, nr 1, s. 45-63Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The aim of this article is to investigate how the formal competence development activities provided by the Production Leap, a workplace development programme (WPDP), were interwoven with everyday work activities and to identify the conditions that enabled learning and employee-driven innovation that contributed to production improvement, in small and medium-sized enterprises (SMEs) in Sweden. The study adopts a qualitative case approach and draws on evidence from research conducted in four manufacturing SMEs that participated in this Swedish WPDP. Funded by EU authorities, WPDPs provide competence development activities to SMEs in order to boost their production capabilities and/or promote innovation. The findings reveal that the competence development activities provided by the programme triggered learning in everyday work activities and fostered the development of different approaches to employee-driven innovation in the enterprises. The conclusion is that it is essential to consider that employee-driven innovations may take different forms and involve functions that can support innovative learning that goes beyond minor adjustments to the existing standards of production. Moreover, employee-driven innovation may impose new demands on management leadership skills. The findings provide important guidance for future WPDPs, for vocational education and training or university activities that are customised to SME contexts to promote production capabilities, and for SMEs that aim to strengthen employee-driven innovation.

    Ort, förlag, år, upplaga, sidor
    Dordrecht: Springer Netherlands, 2018
    Nationell ämneskategori
    Lärande
    Identifikatorer
    urn:nbn:se:liu:diva-137495 (URN)10.1007/s12186-017-9179-6 (DOI)000426597000003 ()
    Forskningsfinansiär
    VINNOVA, 2013-02430
    Anmärkning

    Funding agencies: Swedish Agency for Innovation Systems (VINNOVA) [Vinnova 2013-02430]

    Tillgänglig från: 2017-05-18 Skapad: 2017-05-18 Senast uppdaterad: 2019-02-13Bibliografiskt granskad