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Lilja, Louise
Publications (10 of 14) Show all publications
Lilja, L. (2018). 4H-SiC epitaxy investigating carrier lifetime and substrate off-axis dependence. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>4H-SiC epitaxy investigating carrier lifetime and substrate off-axis dependence
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon carbide (SiC) is a wide bandgap semiconductor with unique material properties making it useful for various device applications using high power, high frequency and high temperature. Compared to Si-based electronics, SiC based electronics have an improved energy efficiency. One of the most critical problems is to reduce this planets power consumption, where large improvements can be made enhancing the energy efficiency. Independent on how the electrical power is generated, power conversion is needed and about 10% of the electrical power is lost for every power conversion step using Si-based electronics. Since the efficiency is related to the performance of the semiconductor device, SiC can make contributions to the efficiency. Compared to Si, SiC has three times larger bandgap, about ten times higher breakdown electric field strength and about three times higher thermal conductivity. The wide bandgap together with the chemical stability of SiC makes it possible for SiC electronic devices to operate at much higher temperatures (>250°C) compared to Si-based devices and do not require large cooling units as with Si power converters.

The current status for 4H-SiC devices regard unipolar devices (≤ 1700 V), such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes (SBDs), are now on the market for mass production. The research focus is now on high-voltage (>10 kV) bipolar devices, such as, bipolar junction transistors (BJTs), p‑i‑n diodes and insulated-gate bipolar transistors (IGBTs).

The focus of this thesis are material improvements relevant for the development of 4H-SiC high-voltage bipolar devices. A key parameter for such devices is the minority carrier lifetime, where long carrier lifetimes reduce the on-resistance through conductivity modulation. However, too long carrier lifetimes give long reverse recovery times leading to large switching losses. Thus, a tailored carrier lifetime is needed for the specific application. Carrier lifetimes of the epilayers can both be controlled by the CVD growth conditions and by post-growth processing, such as thermal oxidation and carbon implantation followed by thermal annealing. Emphasis in this thesis (Paper 1‑2) is to find optimal CVD growth conditions (growth temperature, C/Si ratio, growth rate, doping) improving the carrier lifetime. Since the main lifetime limiting defect has shown to be the Z1/2 center, identified as isolated carbon vacancies, growth conditions minimizing the Z1/2 concentration are strived for.

To achieve high-voltage bipolar devices, thick epilayers of high quality is needed. An important factor is then the growth rate that needs to be relatively high in order to reduce the fabrication time, and thus the cost of the final device. In this thesis the growth process has been optimized for high growth rates (30 µm/h) using standard silane and propane chemistry (Paper 3), compared to other chemistries that includes chlorine, which results in corroded reactor parts and new defects in the epitaxial layers.

Another important parameter for 4H-SiC bipolar devices is the basal plane dislocations (BPDs) in the substrate and epilayers, since the BPDs can act as source of nucleation and expansion of Shockley stacking faults (SSFs). The expanded SSFs give a lowered carrier lifetime and form a potential barrier for carrier transport leading to an increased forward voltage drop which in turn leads to bipolar degradation. The bipolar degradation is detrimental for 4H-SiC bipolar devices. Several strategies are developed to reduce the density of BPDs including buffer layers, growth interrupts and decreasing the substrates off-cut angle. Paper 4‑6 is focused on developing a CVD growth process for low substrate off-cut angles (1° and 2°) compared to the today’s standard off-cut angle of 4°. By reducing the substrate off-cut angle the number of BPDs intersecting the substrate surface is reduced. In addition, the conversion from BPDs to threading edge dislocations (TEDs) during epitaxial growth is increased with lower off-cut angles.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 63
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1960
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-152500 (URN)10.3384/diss.diva-152500 (DOI)9789176851937 (ISBN)
Public defence
2018-12-18, Planck, Fysikhuset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2018-12-10 Created: 2018-11-05 Last updated: 2018-12-10Bibliographically approved
Booker, I. D., Abdalla, H., Hassan, J., Karhu, R., Lilja, L., Janzén, E. & Sveinbjörnsson, E. (2016). Oxidation-induced deep levels in n- and p-type 4H- and 6H-SiC and their influence on carrier lifetime. Physical Review Applied, 6(1), 1-15, Article ID 014010.
Open this publication in new window or tab >>Oxidation-induced deep levels in n- and p-type 4H- and 6H-SiC and their influence on carrier lifetime
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2016 (English)In: Physical Review Applied, ISSN 2331-7019, Vol. 6, no 1, p. 1-15, article id 014010Article in journal (Refereed) Published
Abstract [en]

We present a complete analysis of the electron- and hole-capture and -emission processes of the deep levels ON1, ON2a, and ON2b in 4H-SiC and their 6H-SiC counterparts OS1a and OS1b through OS3a and OS3b, which are produced by lifetime enhancement oxidation or implantation and annealing techniques. The modeling is based on a simultaneous numerical fitting of multiple high-resolution capacitance deep-level transient spectroscopy spectra measured with different filling-pulse lengths in n- and p-type material. All defects are found to be double-donor-type positive-U two-level defects with very small hole-capture cross sections, making them recombination centers of low efficiency, in accordance with minority-carrier-lifetime measurements. Their behavior as trapping and weak recombination centers, their large concentrations resulting from the lifetime enhancement oxidations, and their high thermal stability, however, make it advisable to minimize their presence in active regions of devices, for example, the base layer of bipolar junction transistors.

Place, publisher, year, edition, pages
American Physical Society, 2016
Keywords
Time-resolved photoluminescence, Deep level transient spectroscopy, Minority carrier transient spectroscopy, Lifetime enhancement, Oxidation; Recombination center, 4H-SiC, 6H-SiC
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-121546 (URN)10.1103/PhysRevApplied.6.014010 (DOI)000380125700001 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

At the time for thesis presentation publication was in status: Manuscript

Available from: 2015-09-24 Created: 2015-09-24 Last updated: 2018-09-01Bibliographically approved
Lilja, L., ul-Hassan, J., Janzén, E. & Bergman, J. P. (2016). Smooth 4H-SiC epilayers grown with high growth rates with silane/propane chemistry using 4° off-cut substrates. In: Fabrizio Roccaforte, Francesco La Via, Roberta Nipoti, Danilo Crippa, Filippo Giannazzo and Mario Saggio (Ed.), Silicon Carbide and Related Materials 2015: . Paper presented at The 16th International Conference on Silicon Carbide and Related Materials (ICSCRM2015), Giardini Naxos, Sicily, Italy, October 4th October 9th, 2015. (pp. 209-212). Trans Tech Publications, 858
Open this publication in new window or tab >>Smooth 4H-SiC epilayers grown with high growth rates with silane/propane chemistry using 4° off-cut substrates
2016 (English)In: Silicon Carbide and Related Materials 2015 / [ed] Fabrizio Roccaforte, Francesco La Via, Roberta Nipoti, Danilo Crippa, Filippo Giannazzo and Mario Saggio, Trans Tech Publications, 2016, Vol. 858, p. 209-212Conference paper, Published paper (Refereed)
Abstract [en]

4H-SiC epilayers with very smooth surfaces were grown with high growth rates on 4° off-cut substrates using standard silane/propane chemistry. Specular surfaces with RMS values below 0.2 nm are presented for epilayers grown with growth rates up to 30 μm/h using horizontal hot-wall chemical vapor deposition, with up to 100 μm thickness. Optimization of in-situ etching conditions and C/Si ratio are presented.

Place, publisher, year, edition, pages
Trans Tech Publications, 2016
Series
Materials Science Forum, ISSN 1662-9752 ; 858
Keywords
Atomic force microscopy, Chemical vapor deposition, Epitaxial growth, Silicon carbide
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-153288 (URN)10.4028/www.scientific.net/MSF.858.209 (DOI)
Conference
The 16th International Conference on Silicon Carbide and Related Materials (ICSCRM2015), Giardini Naxos, Sicily, Italy, October 4th October 9th, 2015.
Available from: 2018-12-10 Created: 2018-12-10 Last updated: 2018-12-10
Lilja, L., Ul-Hassan, J., Janzén, E. & Bergman, P. (2015). In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates. Physica status solidi. B, Basic research, 252(6), 1319-1324
Open this publication in new window or tab >>In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates
2015 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, no 6, p. 1319-1324Article in journal (Refereed) Published
Abstract [en]

4H-SiC epilayers were grown on 2 degrees off-cut substrates using standard silane/propane chemistry, with the aim of characterizing in-grown stacking faults. The stacking faults were analyzed with low temperature photoluminescence spectroscopy, room temperature photoluminescence mappings, room temperature cathodoluminescence and synchrotron white beam X-ray topography. At least three different types of in-grown stacking faults were observed, including double Shockley stacking faults, triple Shockley stacking faults and bar-shaped stacking faults. Those stacking faults are all previously found in 4 degrees and 8 degrees off-cut epilayers; however, the geometrical size is larger in epilayers grown on 2 degrees off-cut substrates due to lower off-cut angle. The stacking faults were formed close to the epilayer/substrate interface during the epitaxial growth. (C) 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

Place, publisher, year, edition, pages
WILEY-V C H VERLAG GMBH, 2015
Keywords
chemical vapor deposition; epitaxy; photoluminescence; SiC; stacking faults
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-120065 (URN)10.1002/pssb.201451710 (DOI)000355756200018 ()
Note

Funding Agencies|Swedish Research Council (VR); Advanced Functional Materials (AFM); Swedish Foundation for Strategic Research (SSF)

Available from: 2015-07-06 Created: 2015-07-06 Last updated: 2018-12-10
Han, G., Mueller, W. E. G., Wang, X., Lilja, L. & Shen, Z. (2015). Porous titania surfaces on titanium with hierarchical macro- and mesoporosities for enhancing cell adhesion, proliferation and mineralization. Materials science & engineering. C, biomimetic materials, sensors and systems, 47, 376-383
Open this publication in new window or tab >>Porous titania surfaces on titanium with hierarchical macro- and mesoporosities for enhancing cell adhesion, proliferation and mineralization
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2015 (English)In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 47, p. 376-383Article in journal (Refereed) Published
Abstract [en]

Titanium received a macroporous titania surface layer by anodization, which contains open pores with average pore diameter around 5 gm. An additional mesoporous titania top layer following the contour of the macropores, of 100-200 nm thickness and with a pore diameter of 10 nm, was formed by using the evaporation-induced self-assembly (EISA) method with titanium (IV) tetraethoxide as the precursor. A coherent laminar titania surface layer was thus obtained, creating a hierarchical macro- and mesoporous surface that was characterized by high-resolution electron microscopy. The interfacial bonding between the surface layers and the titanium matrix was characterized by the scratch test that confirmed a stable and strong bonding of titania surface layers on titanium. The wettability to water and the effects on the osteosarcoma cell line (SaOS-2) proliferation and mineralization of the formed titania surface layers were studied systematically by cell culture and scanning electron microscopy. The results proved that the porous titania surface with hierarchical macro- and mesoporosities was hydrophilic that significantly promoted cell attachment and spreading. A synergistic role of the hierarchical macro- and mesoporosities was revealed in terms of enhancing cell adhesion, proliferation and mineralization, compared with the titania surface with solo scale topography.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Porosity; Titanium oxide; Cell adhesion; Cell proliferation; Surface topography
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-114233 (URN)10.1016/j.msec.2014.11.021 (DOI)000347581600045 ()25492210 (PubMedID)
Note

Funding Agencies|European Commission [604036, 215507, 286059, 266033, 268476, 311848]; Knut and Alice Wallenberg foundation; ERC Advanced Investigator Grant [268476]; Deutsche Forschungsgemeinschaft [Schr 277/10-2]; International Human Frontier Science Program; Public Welfare Project of Ministry of Land and Resources of the Peoples Republic of China [201011005-06]; International Science and Technology Cooperation Program of China [2008DFA00980]

Available from: 2015-02-16 Created: 2015-02-16 Last updated: 2017-12-04
Booker, I. D., Ul Hassan, J., Lilja, L., Beyer, F., Karhu, R., Bergman, J. P., . . . Janzén, E. (2014). Carrier Lifetime Controlling Defects Z(1/2) and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC. Crystal Growth & Design, 14(8), 4104-4110
Open this publication in new window or tab >>Carrier Lifetime Controlling Defects Z(1/2) and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC
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2014 (English)In: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, no 8, p. 4104-4110Article in journal (Refereed) Published
Abstract [en]

4H-SiC epilayers grown by standard and chlorinated chemistry were analyzed for their minority carrier lifetime and deep level recombination centers using time-resolved photoluminescence (TRPL) and standard deep level transient spectroscopy (DLTS). Next to the well-known Z(1/2) deep level a second effective lifetime killer, RB1 (activation energy 1.05 eV, electron capture cross section 2 x 10(-16) cm(2), suggested hole capture cross section (5 +/- 2) x 10(-15) cm(2)), is detected in chloride chemistry grown epilayers. Junction-DLTS and bulk recombination simulations are used to confirm the lifetime killing properties of this level. The measured RB1 concentration appears to be a function of the iron-related Fe1 level concentration, which is unintentionally introduced via the corrosion of reactor steel parts by the chlorinated chemistry. Reactor design and the growth zone temperature profile are thought to enable the formation of RB1 in the presence of iron contamination under conditions otherwise optimal for growth of material with very low Z(1/2) concentrations. The RB1 defect is either an intrinsic defect similar to RD1/2 or EH5 or a complex involving iron. Control of these corrosion issues allows the growth of material at a high growth rate and with high minority carrier lifetime based on Z(1/2) as the only bulk recombination center.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2014
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-110278 (URN)10.1021/cg5007154 (DOI)000340080400049 ()
Note

Funding Agencies|The Swedish Energy Agency; Swedish Research Council (VR); Swedish Foundation for Strategic Research (SSF); LG Innotek

Available from: 2014-09-05 Created: 2014-09-05 Last updated: 2017-12-05Bibliographically approved
Kallinger, B., Rommel, M., Lilja, L., ul-Hassan, J., Booker, I. D., Janzén, E. & Bergman, P. (2014). Comparison of carrier lifetime measurements and mapping in 4H SIC using time resolved photoluminescence and μ-PCD. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials, ICSCRM 2013 (pp. 301-304). Stafa-Zurich, Switzerland: Trans Tech Publications, 778-780
Open this publication in new window or tab >>Comparison of carrier lifetime measurements and mapping in 4H SIC using time resolved photoluminescence and μ-PCD
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2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Stafa-Zurich, Switzerland: Trans Tech Publications , 2014, Vol. 778-780, p. 301-304Conference paper, Published paper (Refereed)
Abstract [en]

Carrier lifetime measurements and wafer mappings have been done on several different 4H SiC epiwafers to compare two different measurement techniques, time-resolved photoluminescence and microwave induced photoconductivity decay. The absolute values of the decay time differ by a factor of two, as expected from recombination and measurement theory. Variations within each wafer are comparable with the two techniques. Both techniques are shown to be sensitive to substrate quality and distribution of extended defects.

Place, publisher, year, edition, pages
Stafa-Zurich, Switzerland: Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 0255-5476 ; vol 778-780
Keywords
Carrier lifetime; Photoluminescence; Silicon carbide; μ-PCD
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-110541 (URN)10.4028/www.scientific.net/MSF.778-780.301 (DOI)000336634100071 ()2-s2.0-84896069395 (Scopus ID)9783038350101 (ISBN)
Conference
15th International Conference on Silicon Carbide and Related Materials, ICSCRM 2013
Available from: 2014-09-15 Created: 2014-09-12 Last updated: 2014-09-15
Ul-Hassan, J., Bae, H., Lilja, L., Farkas, I., Kim, I., Stenberg, P., . . . Janzén, E. (2014). Fast growth rate epitaxy on 4((degrees)under-bar) off-cut 4-inch diameter 4H-SiC wafers. In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2: . Paper presented at 15th International Conference on Silicon Carbide and Related Materials (ICSCRM), Miyazaki, Japan, 29 Sptember - 4 October 2013 (pp. 179-182). Trans Tech Publications, 778-780
Open this publication in new window or tab >>Fast growth rate epitaxy on 4((degrees)under-bar) off-cut 4-inch diameter 4H-SiC wafers
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2014 (English)In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 179-182Conference paper, Published paper (Refereed)
Abstract [en]

We report the development of over 100 mu m/h growth rate process on 4-inch diameter wafers using chlorinated growth. The optimized growth process has shown extremely smooth epilayers completely free of surface step-bunching with very low surface defect density, high uniformity in thickness and doping and high run to run reproducibility in growth rate, controlled doping and defect density.

Place, publisher, year, edition, pages
Trans Tech Publications, 2014
Series
Materials Science Forum, ISSN 1662-9752 ; 778-780
Keywords
Fast epitaxial growth; high growth rate; chlorinated growth; atomic force microscopy
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-108193 (URN)10.4028/www.scientific.net/MSF.778-780.179 (DOI)000336634100042 ()
Conference
15th International Conference on Silicon Carbide and Related Materials (ICSCRM), Miyazaki, Japan, 29 Sptember - 4 October 2013
Available from: 2014-06-26 Created: 2014-06-26 Last updated: 2016-06-02Bibliographically approved
Lilja, L., ul-Hassan, J., Booker, I., Bergman, P. & Janzén, E. (2013). Influence of Growth Temperature on Carrier Lifetime in 4H-SiC Epilayers. In: : . Paper presented at 9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St Petersburg, Russia (pp. 637-640). Trans Tech Publications Inc., 740-742
Open this publication in new window or tab >>Influence of Growth Temperature on Carrier Lifetime in 4H-SiC Epilayers
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2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Carrier lifetime and formation of defects have been investigated as a function of growth temperature in n-type 4H-SiC epitaxial layers, grown by horizontal hot-wall CVD. Emphasis has been put on having fixed conditions except for the growth temperature, hence growth rate, doping and epilayer thickness were constant in all epilayers independent of growth temperature. An increasing growth temperature gave higher Z1/2 concentrations along with decreasing carrier lifetime. A correlation between growth temperature and D1 defect was also observed.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2013
Keywords
Atomic Force Microscopy, Carrier Lifetime, DLTS, Epitaxial Growth, Horizontal Hot-Wall CVD, Intrinsic Defect, Photoluminescence (PL)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88341 (URN)10.4028/www.scientific.net/MSF.740-742.637 (DOI)000319785500151 ()
Conference
9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St Petersburg, Russia
Available from: 2013-02-04 Created: 2013-02-04 Last updated: 2018-12-10
ul Hassan, J., Booker, I., Lilja, L., Hallén, A., Fagerlind, M., Bergman, P. & Janzén, E. (2013). On-axis homoepitaxial growth of 4H-SiC PiN structure for high power applications. In: Materials Science Forum (Volumes 740 - 742): . Paper presented at 9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012) (pp. 173-176). Trans Tech Publications Inc.
Open this publication in new window or tab >>On-axis homoepitaxial growth of 4H-SiC PiN structure for high power applications
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2013 (English)In: Materials Science Forum (Volumes 740 - 742), Trans Tech Publications Inc., 2013, p. 173-176Conference paper, Published paper (Refereed)
Abstract [en]

We demonstrate on-axis homoepitaxial growth of 4H-SiC(0001) PiN structure on 3-inch wafers with 100% 4H polytype in the epilayer excluding the edges. The layers were grown with a thickness of 105 µm and controlled n-type doping of 4 x 1014 cm-3. The epilayers were completely free of basal plane dislocations, in-grown stacking faults and other epitaxial defects, as required for 10 kV high power bipolar devices. Some part of the wafer had a lifetime enhancement procedure to increase lifetime to above 2 µs using carbon implantation. An additional step of epilayer polishing was adapted to reduce surface roughness and implantation damage.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2013
Keywords
Carrier Lifetime, Chemical Vapor Deposition (CVD), Growth Mechanism, High Power Devices, On-Axis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-91406 (URN)10.4028/www.scientific.net/MSF.740-742.173 (DOI)000319785500041 ()
Conference
9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012)
Available from: 2013-04-24 Created: 2013-04-24 Last updated: 2013-08-23
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