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BETA
ul-Hassan, Jawad
Alternative names
Publications (10 of 79) Show all publications
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
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
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: 2016-08-22Bibliographically approved
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
Salemi, A., Elahipanah, H., Buono, B., Hallen, A., Ul-Hassan, J., Bergman, P., . . . Ostling, M. (2015). Conductivity Modulated On-axis 4H-SiC 10+kV PiN Diodes. In: 2015 IEEE 27TH INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES and ICS (ISPSD): . Paper presented at 27th International Symposium on Power Semiconductor Devices and ICs (ISPSD) (pp. 269-272). IEEE
Open this publication in new window or tab >>Conductivity Modulated On-axis 4H-SiC 10+kV PiN Diodes
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2015 (English)In: 2015 IEEE 27TH INTERNATIONAL SYMPOSIUM ON POWER SEMICONDUCTOR DEVICES and ICS (ISPSD), IEEE , 2015, p. 269-272Conference paper, Published paper (Refereed)
Abstract [en]

Degradation-free ultrahigh-voltage (> 10 kV) PiN diodes using on-axis 4H-SiC with low forward voltage drop (V-F = 3.3 V at 100 A/cm(2)) and low differential on-resistance (R-ON = 3.4 m Omega.cm(2)) are fabricated, measured, and analyzed by device simulation. The devices show stable on-state characteristics over a broad temperature range up to 300 degrees C. They show no breakdown up to 10 kV, i.e., the highest blocking capability for 4H-SiC devices using on-axis to date. The minority carrier lifetime (tau(P)) is measured after epitaxial growth by time resolved photoluminescence (TRPL) technique at room temperature. The tau(P) is measured again after device fabrication by open circuit voltage decay (OCVD) up to 500 K.

Place, publisher, year, edition, pages
IEEE, 2015
Series
Proceedings of the International Symposium on Power Semiconductor Devices & ICs, ISSN 1063-6854
Keywords
On-axis 4H-SiC; PiN diode; ultrahigh-voltage; lifetime enhancement; V-F; on-resistance; OCVD; breakdown voltage; bipolar degradation-free
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-126278 (URN)000370717300066 ()978-1-4799-6261-7 (ISBN)
Conference
27th International Symposium on Power Semiconductor Devices and ICs (ISPSD)
Available from: 2016-03-21 Created: 2016-03-21 Last updated: 2016-03-21
Westlund, A., Winters, M., Ivanov, I. G., Ul-Hassan, J., Nilsson, P.-A. -., Janzén, E., . . . Grahn, J. (2015). Correction: Graphene self-switching diodes as zero-bias microwave detectors (vol 106, 093116, 2015). Applied Physics Letters, 106(15), Article ID 159902.
Open this publication in new window or tab >>Correction: Graphene self-switching diodes as zero-bias microwave detectors (vol 106, 093116, 2015)
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 15, article id 159902Article in journal (Other academic) Published
Abstract [en]

n/a

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-118246 (URN)10.1063/1.4916581 (DOI)000353160700053 ()
Available from: 2015-06-04 Created: 2015-05-22 Last updated: 2017-12-04
Westlund, A., Winters, M., Ivanov, I. G., Ul-Hassan, J., Nilsson, P.-A. -., Janzén, E., . . . Grahn, J. (2015). Graphene self-switching diodes as zero-bias microwave detectors. Applied Physics Letters, 106(9), 093116
Open this publication in new window or tab >>Graphene self-switching diodes as zero-bias microwave detectors
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 9, p. 093116-Article in journal (Refereed) Published
Abstract [en]

Self-switching diodes (SSDs) were fabricated on as-grown and hydrogen-intercalated epitaxial graphene on SiC. The SSDs were characterized as zero-bias detectors with on-wafer measurements from 1 to 67 GHz. The lowest noise-equivalent power (NEP) was observed in SSDs on the hydrogen-intercalated sample, where a flat NEP of 2.2 nW/Hz(1/2) and responsivity of 3.9 V/W were measured across the band. The measured NEP demonstrates the potential of graphene SSDs as zero-bias microwave detectors. (C) 2015 AIP Publishing LLC.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-117237 (URN)10.1063/1.4914356 (DOI)000351069900061 ()
Note

Funding Agencies|Swedish Research Council [VR 621-2012-4633]; European Science Foundation (ESF) under the EUROCORES Program EuroGRAPHENE (EPIGRAT); Swedish Foundation for Strategic Research (SSF), project "Graphene based high-frequency electronics" [RE10-0077]; Knut and Alice Wallenberg Foundation (KAW), project "Swedish Graphene Initiative"

Available from: 2015-04-22 Created: 2015-04-21 Last updated: 2017-12-04
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: 2017-12-04
Christle, D. J., Falk, A. L., Andrich, P., Klimov, P. V., ul-Hassan, J., Tien Son, N., . . . Awschalom, D. D. (2015). Isolated electron spins in silicon carbide with millisecond coherence times. Nature Materials, 14(2), 160-163
Open this publication in new window or tab >>Isolated electron spins in silicon carbide with millisecond coherence times
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2015 (English)In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 14, no 2, p. 160-163Article in journal (Refereed) Published
Abstract [en]

The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries(1). Nonetheless, because certain SiC defects have electronic states with sharp optical and spin transitions, they are increasingly recognized as a platform for quantum information and nanoscale sensing(2-16). Here, we show that individual electron spins in high-purity monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects(2,3), these states exhibit exceptionally long ensemble Hahn-echo spin coherence times, exceeding 1 ms. Coherent control of single spins in a material amenable to advanced growth and microfabrication techniques is an exciting route towards wafer-scale quantum technologies.

Place, publisher, year, edition, pages
Nature Publishing Group, 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-114989 (URN)10.1038/NMAT4144 (DOI)000348600200011 ()25437259 (PubMedID)
Note

Funding Agencies|NSF; Center for Nanoscale Materials [CNM 39211]; Knut and Alice Wallenberg Foundation; Linkoping Linnaeus Initiative for Novel Functionalized Materials; Swedish Government Strategic Research Area Grant in Materials Science (Advanced Functional Materials); Ministry of Education, Science, Sports and Culture of Japan [26286047]; AFOSR MURI

Available from: 2015-03-11 Created: 2015-03-06 Last updated: 2017-12-04
ul-Hassan, J., Winters, M., Gueorguiev Ivanov, I., Habibpour, O., Zirath, H., Rorsman, N. & Janzén, E. (2015). Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0001) layers. Carbon, 82, 12-23
Open this publication in new window or tab >>Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0001) layers
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2015 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 82, p. 12-23Article in journal (Refereed) Published
Abstract [en]

Quasi-free-standing monolayer and bilayer graphene is grown on homoepitaxial layers of 4H-SiC. The SiC epilayers themselves are grown on the Si-face of nominally on-axis semi-insulating substrates using a conventional SiC hot-wall chemical vapor deposition reactor. The epilayers were confirmed to consist entirely of the 4H polytype by low temperature photoluminescence. The doping of the SiC epilayers may be modified allowing for graphene to be grown on a conducing substrate. Graphene growth was performed via thermal decomposition of the surface of the SiC epilayers under Si background pressure in order to achieve control on thickness uniformity over large area. Monolayer and bilayer samples were prepared through the conversion of a carbon buffer layer and monolayer graphene respectively using hydrogen intercalation process. Micro-Raman and reflectance mappings confirmed predominantly quasi-free-standing monolayer and bilayer graphene on samples grown under optimized growth conditions. Measurements of the Hall properties of Van der Pauw structures fabricated on these layers show high charge carrier mobility (greater than 2000 cm(2)/Vs) and low carrier density (less than0.9 x 10(13) cm(-2)) in quasi-free-standing bilayer samples relative to monolayer samples. Also, bilayers on homoepitaxial layers are found to be superior in quality compared to bilayers grown directly on SI substrates.

Place, publisher, year, edition, pages
Elsevier, 2015
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-113151 (URN)10.1016/j.carbon.2014.10.010 (DOI)000345683100002 ()
Note

Funding Agencies|European Science Foundation (ESF) under the EUROCORES Program EuroGRAPHENE; Swedish Research Councils (VR); Swedish Government Strategic Research Area Grant in Materials Science

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