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ul-Hassan, Jawad
Alternative names
Publications (10 of 86) Show all publications
Ayedh, H. M., Baathen, M. E., Galeckas, A., ul-Hassan, J., Bergman, P., Nipoti, R., . . . Svensson, B. G. (2018). (Invited) Controlling the Carbon Vacancy in 4H-SiC by Thermal Processing. ECS Transactions, 86(12), 91-97
Open this publication in new window or tab >>(Invited) Controlling the Carbon Vacancy in 4H-SiC by Thermal Processing
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2018 (English)In: ECS Transactions, ISSN 1938-5862, E-ISSN 1938-6737, ECS Transactions, Vol. 86, no 12, p. 91-97Article in journal (Refereed) Published
Abstract [en]

The carbon vacancy (VC) is perhaps the most prominent point defect in silicon carbide (SiC) and it is an efficient charge carrier lifetime killer in high-purity epitaxial layers of 4H-SiC. The VC concentration needs to be controlled and minimized for optimum materials and device performance, and an approach based on post-growth thermal processing under C-rich ambient conditions is presented. It utilizes thermodynamic equilibration and after heat treatment at 1500 °C for 1 h, the VC concentration is shown to be reduced by a factor ~25 relative to that in as-grown state-of-the-art epi-layers. Concurrently, a considerable enhancement of the carrier lifetime occurs throughout the whole of >40 µm thick epi-layers.

Place, publisher, year, edition, pages
Electrochemical Society, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-160924 (URN)10.1149/08612.0091ecst (DOI)2-s2.0-85058420747 (Scopus ID)
Available from: 2019-10-15 Created: 2019-10-15 Last updated: 2019-10-21Bibliographically approved
Lilja, L., Farkas, I., Booker, I., ul-Hassan, J., Janzén, E. & Bergman, P. (2017). Influence of n-Type Doping Levels on Carrier Lifetime in 4H-SiC Epitaxial Layers. In: Silicon Carbide and Related Materials 2016: . Paper presented at 11th European Conference on Silicone Carbide & Related Materials, Halkidiki, Greece, 25-29 September, 2016 (pp. 238-241). Trans Tech Publications Ltd, 897
Open this publication in new window or tab >>Influence of n-Type Doping Levels on Carrier Lifetime in 4H-SiC Epitaxial Layers
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2017 (English)In: Silicon Carbide and Related Materials 2016, Trans Tech Publications Ltd , 2017, Vol. 897, p. 238-241Conference paper, Published paper (Refereed)
Abstract [en]

In this study we have grown thick 4H-SiC epitaxial layers with different n-type doping levels in the range 1E15 cm-3 to mid 1E18 cm-3, in order to investigate the influence on carrier lifetime. The epilayers were grown with identical growth conditions except the doping level on comparable substrates, in order to minimize the influence of other parameters than the n-type doping level. We have found a drastic decrease in carrier lifetime with increasing n-type doping level. Epilayers were further characterized with low temperature photoluminescence and deep level transient spectroscopy.

Place, publisher, year, edition, pages
Trans Tech Publications Ltd, 2017
Series
Materials Science Forum, ISSN 1662-9752
Keywords
Auger Recombination, Carrier Lifetime, Epitaxial Growth, Chemical Vapor Deposition (CVD), Photoluminescence
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160906 (URN)10.4028/www.scientific.net/MSF.897.238 (DOI)2-s2.0-85020038744 (Scopus ID)
Conference
11th European Conference on Silicone Carbide & Related Materials, Halkidiki, Greece, 25-29 September, 2016
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-24Bibliographically approved
Khosa, R. Y., Sveinbjörnsson, E., Winters, M., ul-Hassan, J., Karhu, R., Janzén, E. & Rorsman, N. (2017). Low Density of Near-Interface Traps at the Al2O3/4H-SiC Interface with Al2O3 Made by Low Temperature Oxidation of Al. In: Silicon Carbide and Related Materials 2016: . Paper presented at 11th European Conference on Silicone Carbide & Related Materials, Halkidiki, Greece, 25-29 September, 2016 (pp. 135-138). Trans Tech Publications Ltd, 897
Open this publication in new window or tab >>Low Density of Near-Interface Traps at the Al2O3/4H-SiC Interface with Al2O3 Made by Low Temperature Oxidation of Al
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2017 (English)In: Silicon Carbide and Related Materials 2016, Trans Tech Publications Ltd , 2017, Vol. 897, p. 135-138Conference paper, Published paper (Refereed)
Abstract [en]

We report on a very low density (<5×1011 cm-2) of near-interface traps (NITs) at the Al2O3/4H-SiC interface estimated from capacitance-voltage (CV) analysis of MOS capacitors at different temperatures. The aluminum oxide (Al2O3) is grown by repeated deposition and subsequent low temperature (200°C) oxidation for 5 min of thin (1-2 nm) Al layers using a hot plate. We refer to this simple method as hot plate Al2O3. It is observed that the density of NITs is significantly lower in the hot plate Al2O3 samples than in samples with Al2O3 grown by atomic layer deposition (ALD) at 300°C and in reference samples with thermally grown silicon dioxide grown in O2 or N2O ambient.

Place, publisher, year, edition, pages
Trans Tech Publications Ltd, 2017
Series
Materials Science Forum
Keywords
Gate Dielectrics, Aluminum Oxide, Interface States, Near-Interface Traps (NITs)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-160907 (URN)10.4028/www.scientific.net/MSF.897.135 (DOI)2-s2.0-85020132120 (Scopus ID)
Conference
11th European Conference on Silicone Carbide & Related Materials, Halkidiki, Greece, 25-29 September, 2016
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-24Bibliographically approved
Booker, I. D., Farkas, I., Ivanov, I. G., Ul Hassan, J. & Janzén, E. (2016). Chloride-based SiC growth on a-axis 4H-€“SiC substrates. Paper presented at 6th South African Conference on Photonic Materials (SACPM 2015), Mabula Game Lodge, South Africa, 4 – 8 May 2015. Physica. B, Condensed matter, 480, 23-25
Open this publication in new window or tab >>Chloride-based SiC growth on a-axis 4H-€“SiC substrates
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2016 (English)In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 480, p. 23-25Article in journal (Refereed) Published
Abstract [en]

Abstract SiC has, during the last few years, become increasingly important as a power-device material for high voltage applications. The thick, low-doped voltage-supporting epitaxial layer is normally grown by CVD on 4° off-cut 4H–SiC substrates at a growth rate of 5 – 10 ÎŒ m / h using silane (SiH4) and propane (C3H8) or ethylene (C2H4) as precursors. The concentrations of epitaxial defects and dislocations depend to a large extent on the underlying substrate but can also be influenced by the actual epitaxial growth process. Here we will present a study on the properties of the epitaxial layers grown by a Cl-based technique on an a-axis (90° off-cut from c-direction) 4H–SiC substrate.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
4H–SiC; a-face; DLTS; Photoluminescence; Raman; Epitaxy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-123948 (URN)10.1016/j.physb.2015.08.038 (DOI)000365600300005 ()
Conference
6th South African Conference on Photonic Materials (SACPM 2015), Mabula Game Lodge, South Africa, 4 – 8 May 2015
Available from: 2016-01-14 Created: 2016-01-14 Last updated: 2017-11-30Bibliographically approved
Bernardin, E., Frewin, C. L., Dey, A., Everly, R., Ul Hassan, J., Janzén, E., . . . Saddow, S. E. (2016). Development of an all-SiC neuronal interface device. MRS Advances, 1(55), 3679-3684
Open this publication in new window or tab >>Development of an all-SiC neuronal interface device
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2016 (English)In: MRS Advances, ISSN 2059-8521, Vol. 1, no 55, p. 3679-3684Article in journal (Refereed) Published
Abstract [en]

The intracortical neural interface (INI) is a key component of brain machine interfaces (BMI) which offer the possibility to restore functions lost by patients due to severe trauma to the central or peripheral nervous system. Unfortunately today’s neural electrodes suffer from a variety of design flaws, mainly the use of non-biocompatible materials based on Si or W with polymer coatings to mask the underlying material. Silicon carbide (SiC) is a semiconductor that has been proven to be highly biocompatible, and this chemically inert, physically robust material system may provide the longevity and reliability needed for the INI community. The design, fabrication, and preliminary testing of a prototype all-SiC planar microelectrode array based on 4H-SiC with an amorphous silicon carbide (a-SiC) insulator is described. The fabrication of the planar microelectrode was performed utilizing a series of conventional micromachining steps. Preliminary data is presented which shows a proof of concept for an all-SiC microelectrode device.

Place, publisher, year, edition, pages
Cambridge University Press, 2016
National Category
Materials Chemistry
Identifiers
urn:nbn:se:liu:diva-160908 (URN)10.1557/adv.2016.360 (DOI)000412692300004 ()2-s2.0-85029850488 (Scopus ID)
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-21Bibliographically approved
Booker, I. D., Janzén, E., Son, N. T., Hassan, J., Stenberg, P. & Sveinbjörnsson, E. (2016). Donor and double donor transitions of the carbon vacancy related EH6/7 deep level in 4H-SiC. Journal of Applied Physics, 119(23), Article ID 235703.
Open this publication in new window or tab >>Donor and double donor transitions of the carbon vacancy related EH6/7 deep level in 4H-SiC
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2016 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 23, article id 235703Article in journal (Refereed) Published
Abstract [en]

Using medium- and high-resolution multi-spectra fitting of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), optical O-DLTS and optical-electrical (OE)-MCTS measurements, we show that the EH6∕7 deep level in 4H-SiC is composed of two strongly overlapping, two electron emission processes with thermal activation energies of 1.49 eV and 1.58 eV for EH6 and 1.48 eV and 1.66 eV for EH7. The electron emission peaks of EH7 completely overlap while the emission peaks of EH6 occur offset at slightly different temperatures in the spectra. OE-MCTS measurements of the hole capture cross section σp 0(T) in p-type samples reveal a trap-Auger process, whereby hole capture into the defect occupied by two electrons leads to a recombination event and the ejection of the second electron into the conduction band. Values of the hole and electron capture cross sections σn(T) and σp(T) differ strongly due to the donor like nature of the deep levels and while all σn(T) have a negative temperature dependence, the σp(T) appear to be temperature independent. Average values at the DLTS measurement temperature (∼600 K) are σn 2+(T) ≈ 1 × 10−14 cm2, σn +(T) ≈ 1 × 10−14 cm2, and σp 0(T) ≈ 9 × 10−18 cm2 for EH6 and σn 2+(T) ≈ 2 × 10−14 cm2, σn +(T) ≈ 2 × 10−14 cm2, σp 0(T) ≈ 1 × 10−20 cm2 for EH7. Since EH7 has already been identified as a donor transition of the carbon vacancy, we propose that the EH6∕7 center in total represents the overlapping first and second donor transitions of the carbon vacancy defects on both inequivalent lattice sites.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016
Keywords
4H-SiC, DLTS, MCTS, Carbon vacancy, EH6/7; Z1/2, UT-1, Negative-U, Trap Auger, Deep level
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-121544 (URN)10.1063/1.4954006 (DOI)000379038800035 ()
Funder
Swedish Foundation for Strategic Research Swedish Research Council
Note

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

Funding agencies: Swedish Foundation for Strategic Research (SSF); Swedish Research Council (VR)

Available from: 2015-09-24 Created: 2015-09-24 Last updated: 2017-12-01Bibliographically approved
Karhu, R., Booker, I., Ivanov, I. G., Janzén, E. & ul-Hassan, J. (2016). Long Charge Carrier Lifetime in As-Grown 4H-SiC Epilayer. Materials Science Forum, 858, 125-128
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
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, 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: 2019-01-10
Winters, M., Habibpour, O., Gueorguiev Ivanov, I., ul-Hassan, J., Janzén, E., Zirath, H. & Rorsman, N. (2015). Assessment of H-intercalated graphene for microwave FETs through material characterization and electron transport studies. Carbon, 81, 96-104
Open this publication in new window or tab >>Assessment of H-intercalated graphene for microwave FETs through material characterization and electron transport studies
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2015 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 81, p. 96-104Article in journal (Refereed) Published
Abstract [en]

Epitaxial graphene is grown on semi-insulating (SI) 4H-SiC in a hot wall CVD reactor by graphitization and in-situ intercalation with (H)ydrogen. A holistic material characterization is performed in order to ascertain the number of layers, layer uniformity, and electron transport properties of the epi-layers via electronic test structures and Raman spectroscopy. Bilayer graphene field effect transistors (GFETs) are fabricated using a full electron beam lithography (EBL) process which is optimized for low contact resistances of r(c) less than 0.2 Omega mm. Mobilities of order 2500 cm(2)/V s are achieved on bilayer samples after fabrication. The devices demonstrate high transconductance g(m) = 400 mS/mm and high current density I-ds = 1.8 A/mm. The output conductance at the bias of maximum transconductance is g(ds) = 300 mS/mm. The GFETs demonstrate an extrinsic f(t)(ext) and f(max)(ext) of 20 and 13 GHz, respectively and show 6 dB power gain at 1 GHz in a 50 Omega system, which is the highest reported to date.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-113163 (URN)10.1016/j.carbon.2014.09.029 (DOI)000345682900011 ()
Note

Funding Agencies|European Science Foundation (ESF) under the EUROCORES Program EuroGRAPHENE; EU Graphene Flagship [604391]; Swedish Foundation for Strategic Research (SSF); Knut and Alice Wallenberg Foundation (KAW); EPIGRAT project

Available from: 2015-01-14 Created: 2015-01-12 Last updated: 2017-12-05
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