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Welcome to Functional Electronic Materials

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In the Division of Functional Electronic Materials, we conduct scientific research on electronic, magnetic and photonic semiconductor materials and nanostructures. The materials systems currently under study include novel spintronic materials, advanced electronic and photonic materials based on wide bandgap semiconductors and highly mismatched semiconductors, and semiconductor nanostructures.

The research is carried out mostly through a close collaboration with many groups worldwide. Our aim is to obtain a better understanding of fundamental physical properties and a good control of materials properties, and to fully explore functionality of the studied materials for applications in future generation micro- and nano-electronics and photonics as well as in potential multifunctional devices and systems.

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Turning ZnO into an Efficient Energy Upconversion Material by Defect Engineering

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Jan E. Stehr, Shula L. Chen, Nandanapalli Koteeswara Reddy, Charles W. Tu, Weimin M. Chen and Irina A. Buyanova

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Published in Advanced Functional Materials DOI: 10.1002/adfm.201400220

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Photon upconversion materials are attractive for a wide range of applications from medicine, biology, to photonics. Among them, ZnO is of particular interest owing to its outstanding combination of materials and physical properties. Though energy upconversion has been demonstrated in ZnO, the exact physical mechanism is still unknown, preventing control of the processes. Here, defects formed in bulk and nanostructured ZnO synthesized using standard growth techniques play a key role in promoting efficient energy upconversion via two-step two-photon absorption (TS-TPA). From photoluminescence excitation of the anti-Stokes emissions, the threshold energy of the TS-TPA process is determined as being 2.10–2.14 eV in all studied ZnO materials irrespective of the employed growth techniques. This photo-electron paramagnetic resonance studies show that this threshold closely matches the ionization energy of the zinc vacancy (a common grown-in intrinsic defect in ZnO), thereby identifying the zinc vacancy as being the dominant defect responsible for the observed efficient energy upconversion. The upconversion is found to persist even at a low excitation density, making it attractive for photonic and photovoltaic applications.

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Semi-metallic polymers

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Olga Bubnova, Zia Ullah Khan, Hui Wang, Slawomir Braun, Drew R. Evans, Manrico Fabretto, Pejman Hojati-Talemi, Daniel Dagnelund, Jean-Baptiste Arlin, Yves H. Geerts, Simon Desbief,   Dag W. Breiby, Jens W. Andreasen, Roberto Lazzaroni, Weimin M. Chen, Igor Zozoulenko, Mats Fahlman, Peter J. Murphy, Magnus Berggren & Xavier Crispin

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Published in Nature Materials 13, 190–194 (2014) doi:10.1038/nmat3824

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Polymers are lightweight, flexible, solution-processable materials that are promising for low-cost printed electronics as well as for mass-produced and large-area applications. Previous studies demonstrated that they can possess insulating, semiconducting or metallic properties; here we report that polymers can also be semi-metallic. Semi-metals, exemplified by bismuth, graphite and telluride alloys, have no energy bandgap and a very low density of states at the Fermi level. Furthermore, they typically have a higher Seebeck coefficient and lower thermal conductivities compared with metals, thus being suitable for thermoelectric applications.We measure the thermoelectric properties of various poly(3,4-ethylenedioxythiophene) samples, and observe a marked increase in the Seebeck coefficient when the electrical conductivity is enhanced through molecular organization. This initiates the transition from a Fermi glass to a semi-metal. The high Seebeck value, the metallic conductivity at room temperature and the absence of unpaired electron spins makes polymer semi-metals attractive for thermoelectrics and spintronics.

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Media interest:

” Polymers can be semimetals”, Monica Westman Svenselius, LiU news, 2013-12-09.

” Polymerer kan vara halvmetaller”, Monica Westman Svenselius, LiU news, 2013-12-09.

” Polymers can be semimetals”, Phys Org, Dec.9 2013.

” Polymers can behave like insulators, semiconductors and metals -- as well as semimetals”, ScienceDaily, Dec.9 2013.

”Polymers can be semimetals”, Materialstoday, 11 Dec 2013.


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Efficient room-temperature nuclear spin hyperpolarization of defect atom in a semiconductor

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Yuttapoom Puttisong, Xingjun Wang, Irina A. Buyanova, L. Geelhaar, H. Riechert, A. J. Ptak, C. W. Tu and Weimin. M. Chen

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Published in Nature Communications DOI: 10.1038/ncomms2776

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Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we demonstrate that a combined effect of efficient spin-dependent recombination and hyperfine coupling can facilitate strong dynamic nuclear polarization of a defect atom in a semiconductor at room temperature. We provide direct evidence that a sizeable nuclear field (~150 Gauss) and nuclear spin polarization (~15%) sensed by conduction electrons in GaNAs originates from dynamic nuclear polarization of a Ga interstitial defect. We further show that the dynamic nuclear polarization process is remarkably fast and is completed in <5 μs at room temperature. The proposed new concept could pave a way to overcome a major obstacle in achieving strong dynamic nuclear polarization at room temperature, desirable for practical device applications.

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Media interest:

“Ett steg närmare kvantdatorn”, by Monica Westman Svenselius, LiU Nyheter, 2013-04-26

“One step closer to a quantum computer”, by Monica Westman Svenselius, LiU Nyheter, 2013-04-26

“One Step Closer to a Quantum Computer”, Science Daily, April 30 2013

“Success in initializing and reading nuclear spins brings quantum computer a step closer”, PhysOrg, April 30 2013.


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Room-temperature electron spin amplifier based on Ga(In)NAs alloys

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Yuttapoom Puttisong, Irina A. Buyanova, A. J. Ptak, C. W. Tu, L. Geelhaar, H. Riechert and Weimin M. Chen

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Published in Advanced Materials DOI: 10.1002/adma.201202597

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The first experimental demonstration of a spin amplifier at room temperature is presented. An efficient, defect-enabled spin amplifier based on a non-magnetic semiconductor, Ga(In)NAs, is proposed and demonstrated, with a large spin gain (up to 2700% at zero field) for conduction electrons and a high cut-off frequency up to 1 GHz.

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Media interest:

“Viktigt framsteg inom spinntronik”, by Åke Hjelm, LiU Nyheter, Nov.15 2012

“Important advance for spintronics”, by Åke Hjelm, LiU Nyheter, Nov.15 2012

“Första spinnförstärkaren i rumstemperatur”, by Charlotta von Schultz, NyTeknik, 14 november 2012.

”Genombrott: spinnförstärkare i rumstemperatur”, by Jan Tångring, Elektronik Tidningen, Nov.14 2012

“Important Progress for Spintronics: Spin Amplifier Works at Room Temperature”, ScienceDaily (Nov. 16, 2012)

“Important progress for spintronics: A spin amplifier to be used in room temperature”, PhysOrg (Nov.16 201)


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Handbook of Spintronic Semiconductors

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edited by Weimin M Chen and Irina A Buyanova

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Published in Spring 2010 by Pan Stanford Publishing. 400 pages (approx.) ISBN 978-981-4267-36-6

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Room-temperature defect-engineered spin filter based on a non-magnetic semiconductor

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Xingjun J. Wang, Irina A. Buyanova, F. Zhao, D. Lagarde, A. Balocchi, X. Marie, C. W. Tu, J. C. Harmand and Weimin M. Chen

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Published in Nature Materials 8, 198 (2009).

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LiU E-Press offers a free parallel publication.

En översikt på svenska finns i LiUs nyhets-arkiv.

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Media interest:

“Filter gör spinntroniken användbar”, by Hanna Meerveld, Naturvetarna, May 4 2009

“Elektroner spinner i takt i Linköping”, by Anna Wennberg, Elektronik Tidningen, Feb.16 2009

“Stort framsteg för spinntroniken”, by Åke Hjelm, LiU Nyheter, Feb.17 2009

“Great progress for spintronics”, Swedish Research, March 4, 2009


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Effect of Ni-coating on ZnO nanowires: A raman scattering study

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Stanislav Filippov, Xingjun Wang, M. Devika, N. Koteeswara Reddy, C. W. Tu, Weimin. M. Chen and Irina. A. Buyanova.

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Published in J. Appl. Phys. 113, 214302 (2013)

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Optical properties of GaP/GaNP core/shell nanowires: A temperature-dependent study

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Alexander Dobrovolsky, Shula Chen, Yanjin Kuang,Supanee Sukrittanon, Charles W Tu, Weimin M Chen and irina Buyanova

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Published in Nanoscale Research Letters 2013,8:239

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Dynamics of donor bound excitons in ZnO

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Shula Chen, Weimin M. Chen and Irina A. Buyanova

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Published in Appl. Phys. Lett. 102, 121103 (2013)

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Defects in N, O and N, Zn implanted ZnO bulk crystals

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Jan Stehr , Xingjun Wang , Stanislav Filippo v, S. J. Pearton , I. G. Ivanov , Weimin M. Chen , and Irina A. Buyanova
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Published in J. Appl. Phys. 113, 103509 (2013)

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Effect of hyperfine-induced spin mixing on the defect-enabled spin blockade and spin filtering in GaNAs

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Yuttapoom Puttisong, Xingjun Wang, Irina A. Buyanova and Weimin M. Chen

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Published in Phys. Rev. B 87, 125202 (2013)

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Optically detected magnetic resonance studies of point defects in quaternary GaNAsP epilayers grown by vapor phase epitaxy

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Daniel Dagnelund , Jan Stehr , A. Yu. Egorov , Weimin M. Chen , and Irina A. Buyanova
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Published in Appl. Phys. Lett. 102, 021910 (2013)

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Zeeman splitting and dynamics of an isoelectronic bound exciton near the band edge of ZnO

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The first detailed study of an exciton bound to an isoelectronic center

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Shula Chen, Weimin M. Chen and Irina A. Buyanova

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Published in Phys. Rev. B 86, 235205 (2012)

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Defect properties of ZnO nanowires revealed from an optically detected magnetic resonance study

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Jan E. Stehr, Shula Chen, Stanislav Filippov, M. Devika, N. Koteeswara Reddy, C. W. Tu, Weimin M. Chen and Irina A. Buyanova

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Published in Nanotechnology 24, 015701 (2013)

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Sub-millisecond dynamic nuclear spin hyperpolarization in a semiconductor: A case study from PIn antisite in InP

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Xingjun Wang, Irina A. Buyanova and Weimin Chen

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Published in Phys. Rev. B 86, 205202 (2012)

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Mechanism for radiative recombination and defect properties of GaP/GaNP core/shell nanowires

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Alexander Dobrovolsky , Jan Stehr , Shula Chen , Y. J. Kuang , S. Sukrittanon , C. W. Tu , Weimin M. Chen , and Irina A. Buyanova
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Published in Appl. Phys. Lett. 101, 163106 (2012)

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Evidence for coupling between exciton emissions and surface plasmon in Ni-coated ZnO nanowires

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Qejun Ren, Stanislav Filippov, Shula Chen, M. Devika, N. Koteeswara Reddy, C. W. Tu, Weimin M. Chen and Irina A. Buyanova

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Published in Nanotechnology 23 425201 (2012)

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Surface plasmons are used to enhance light emission from ZnO/transition metal core/shell nanowires


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Efficient upconversion of photoluminescence via two-photon absorption in bulk and nanorod ZnO

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Shula Chen, Jan Stehr, N. Koteeswara Reddy, C. W. Tu, Weimin M. Chen and Irina A. Buyanova

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Published in Applied Physics B: Lasers and Optics 2012, DOI: 10.1007/s00340-012-5138-y
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Deeper understanding of different up-conversion mechanisms in ZnO


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Long delays of light in ZnO caused by exciton-polariton propagation

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 Shula chen, Weimin M. Chen and Irina A. Buyanova

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Published in Physica Status Solidi (b) 249, 1307 (2012)
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This article has been selected as Editor Choice in Physica Status Solidi b : basic solid state physics with a back cover page of this journal in volume 249, issue 7, July 2012

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Antiferromagnetic interaction in coupled CdSe/ZnMnSe quantum dot structures

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 Daniel Dagnelund, Q. J. Ren, Irina A. Buyanova, A. Murayama, and Weimin M. Chen

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Published in Applied Physics Letters 101, 052405 (2012)

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Uncover the exact mechanism for magnetic coupling in QD structures


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Temperature dependence of dynamic nuclear polarization and its effect on electron spin relaxation and dephasing in InAs/GaAs quantum dots

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Jan Beyer, Yuttapoom Puttisong, Irina A. Buyanova, S. Suraprapapich, C. W. Tu, and Weimin M. Chen

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Published in Applied Physics Letters 100, 143105 (2012)

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Towards identification of the dominant electron spin relaxation process at elevated temperatures


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The Hanle effect and electron spin polarization in InAs/GaAs quantum dots up to room temperature

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Jan Beyer , Irina A. Buyanova , S. Suraprapapich , C. W. Tu  and Weimin M Chen

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Published in Nanotechnology 23, 135705 (2012)

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What determine spin polarization at room temperature


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Effects of a longitudinal magnetic field on spin injection and detection in InAs/GaAs quantum dot structures

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  Jan Beyer , P. H. Wang ,  Irina A. Buyanova , S. Suraprapapich , C. W. Tu  and Weimin M. Chen

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Published in Journal of Physics: Condensed Matter 24, 145304 (2012)

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Revealing the factors limiting spin injection and spin detection efficiency


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This paper has been selected as an invited IOP journal highlights article in 2012

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Effects of P implantation and post-implantation annealing on defect formation in ZnO

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Xingjun Wang, Weimin M. Chen, F. Ren, S. Pearton, and Irina A. Buyanova

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Published in Journal of Applied Physics 111, 043520 (2012)

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Identification of dominant defects and their role in materials properties


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Efficient room-temperature spin detector based on GaNAs

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Yuttapoom Puttisong, Irina A. Buyanova, L. Geelhaar, H. Riechert, C. W. Tu, and Weimin M. Chen

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Published in Journal of Applied Physics 111, 07C303 (2012)

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Most efficient room-temperature spin detector to date


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Effects of hydrogenation on non-radiative defects in GaNP and GaNAs alloys: An optically detected magnetic resonance study

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 Daniel Dagnelund, I. P. Vorona, G. Nosenko, Xingjun Wang, C. W. Tu, H. Yonezu, A. Polimeni, M. Capizzi, Weimin M. Chen, and Irina A Buyanova

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Published in Journal of Applied Physics 111, 023501 (2012)

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Remarkable and surprising difference revealed between GaNP and GaNAs


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Responsible for this page: Stanislav Filippov, Yuttapoom Puttisong
Last updated: 04/02/14