The research focus of the group is the study of defects in semiconductor materials in order to explain their effects on electrical and optical properties of semiconductor devices.

Defects in semiconductors

The semiconductors in research focus are group IV materials (Si, Ge, SiC, GeSn); III-V materials (e.g. (In,Ga)As) and ternary and quaternary chalcogenide materials (e.g. Cu(In,Ga)Se2, Cu2ZnGeS4)), with applications in microelectronics, optoelectronics and photovoltaics (solar cells).

Defects are investigated through the electronic energy levels they introduce in the bandgap of the semiconductor, and through their vibrational (local vibrational modes (LVM)) and electron magnetic resonance (EPR, ENDOR) spectra.

We aim at structural identification of defects, at their quantification and at understanding their impact on material and device properties. 

The characterization techniques we focus on, are

  • Electron paramagnetic resonance (EPR)
  • Fourier-transform infrared spectroscopy (FTIR)
  • Deep-level transient spectroscopy (DLTS)

Research topics

  • Characterization of point and extended defects in group IV and compound semiconductors
  • Structural, electric and optical characterization of thin-film solar cells
  • Vibrational mode study of Metal-Organic Frameworks in Mid- and Far-IR

Running and recent projects

  • Electrical and physical characterization of trap states at the SiC/gate dielectric interface in SiC metal-oxide-semiconductor field-effect transistors

    This research project is financed by the Vlaio agency for innovation and entrepreneurship (VLAIO - Vlaanderen), through the Baekeland scholarship of Jan Lettens. It involves a scientific collaboration between the University of Antwerp, Ghent University and ON-Semiconductor.

    Promoters: Sofie Cambré (UAntwerpen) and Henk Vrielinck (UGent)
  • Wide-range multi-purpose Fourier-Transform Infrared spectrometer for Materials, Archaeological and Geological Research (FT-IMAGER)

    Via this Hercules-1 (FWO) project (AUGE/13/16), a combined Fourier-Transform Infrared spectrometer and microscope operating in the 10 cm-1 – 15000 cm-1 wavenumber range has become available at UGent. This instrument is used in a very broad range of research topics of the promoters and catalyzes new scientific collaborations within Ghent University, with other Universities and research institutions.

    The research website of this project can be found here.

    Promoters: Henk Vrielinck, Klaartje De Buysser, Johan Lauwaert, Stephen Louwye, Kenneth Mertens, Gűnther Roelkens, Peter Vandenabeele and Pascal Van Der Voort.

    One particular research theme we have focused on within this project, in collaboration with the COMOC research group and the CMM, is characterization of the vibrational modes of metal-organic frameworks, with special attention for the low-frequency modes in the far infrared.

    Selected Publications

    Attenuated total reflection (ATR) micro-Fourier transform infrared (Micro-FT-IR) spectroscopy to enhance repeatability and reproducibility of spectra derived from single specimen organic-walled dinoflagellate cysts

    Pjotr Meyvisch (UGent) , Pieter Gurdebeke (UGent) , Henk Vrielinck (UGent) , Kenneth Neil Mertens, Gerard Versteegh and Stephen Louwye (UGent)


    Fructosamine-3-kinase as a potential treatment option for age-related macular degeneration

    Sander De Bruyne, Caroline Van den Broecke (UGent) , Henk Vrielinck (UGent) , Samira Khelifi (UGent) , Olivier De Wever (UGent) , Ken Bracke (UGent) , Manon Huizing, Nezahat Boston, Jonas Himpe (UGent) , Marijn Speeckaert (UGent) , et al.


    Elucidating the vibrational fingerprint of the flexible metal-organic framework MIL-53(Al) using a combined experimental/computational approach

    Alexander Hoffman (UGent) , Louis Vanduyfhuys (UGent) , Irena Nevjestic (UGent) , Jelle Wieme (UGent) , Sven Rogge (UGent) , Hannes Depauw (UGent) , Pascal Van Der Voort (UGent) , Henk Vrielinck (UGent) and Veronique Van Speybroeck (UGent)

    (2018) JOURNAL OF PHYSICAL CHEMISTRY C. 122(5). p.2734-2746

  • Identification of electrically active defects in materials for solar cells

    The purpose of this project funded by the Ghent University Special Research Fund is to identify defects in the absorber layer of solar cells, which limit the efficiency of the cells. The research focuses on thin film solar cells, mainly with CuIn1-xGaxSe2 absorber. Defects in solar cells and absorber bulk materials are characterized electrically using Deep-Level Transient and Admittance spectroscopy, optically via Fourier-Transform infrared and Infrared photoluminescence (PL) spectroscopy and structurally. The results of this research help directing the optimization of solar cells of this type.

    Within this research project we established that the so-called N1 DLTS signal is due to a non-ideal electric contact (non-ohmic, rectifying electric contact) in the cell, rather than to point defects promoting recombination. Furthermore, solar cells with CuIn1-xGaxSe2 and Cu2ZnSnS4 absorbers were characterized, mainly using PL and PL excitation spectroscopy. This research was performed in collaboration with EMPA Zűrich and the Angstrom Solar Center of Uppsala University and led to the PhD thesis of Lisanne Van Puyvelde Electric and optical defect characterisation of Cu2ZnSnS4 and CuIn1-xGaxSe2 based thin-film solar cells.

    Publications Lisanne Van Puyvelde
    Temperature dependence of the PL and PL excitation (PLE) spectrum of a Cu2ZnSnS4 solar cell as a function of temperature. Van Puyvelde et al. Thin Solid Films 582, p. 146-150 (2015).

    Thin-film solar cells remain an active research area in the group. Currently, we are focusing on studying and analyzing the formation of secondary/ternary phases in thin-film solar cells based on chalcogenide and kesterite materials. Also within the thin-film solar cell technology, perovskite are considered as potential materials for PV application, however they show environmental stability issues when they are subjected to moisture, oxygen, light and heat. As part of our research activities, perovskite materials and solar cells devices are investigated using several characterization techniques in order to tackle these issues and explore solutions for device stability and extend their lifetime.

    Selected publications

    The path towards efficient wide band gap thin-film kesterite solar cells with transparent back contact for viable tandem application

    Samira Khelifi (UGent) , Guy Brammertz, Léo Choubrac, Maria Batuk, Sheng Yang (UGent) , Marc Meuris, Nicolas Barreau, Joke Hadermann, Henk Vrielinck (UGent) , Dirk Poelman (UGent) , et al.


    Effect of Na and the back contact on Cu2Zn(Sn,Ge)Se4 thin-film solar cells: towards semi-transparent solar cells

    Andrea Ruiz-PeronaYudania SanchezMaxim GucSamira Khelifi (UGent), et al.

    (2020) SOLAR ENERGY 206, 555-563.

    Wide band gap kesterite absorbers for thin film solar cells: potential and challenges for their deployment in tandem devices

    Bart Vermang, Guy Brammertz, Marc Meuris, Thomas Schnabel, Erik Ahlswede, Leo Choubrac, Sylvie Harel, Christophe Cardinaud, Ludovic Arzel, Nicolas Barreau, Joop Van Deelen, Pieter-Jan Bolt, Patrice Bras, Yi Ren, Eric Jaremalm, Samira Khelifi et al.

    (2019) Sustainable Energy & Fuels 3 (9), 2246-2259

  • Study of the properties of the intrinsic points defects in monocrystalline germanium

    This FWO research project aimed at identifying and determining the thermodynamic properties of intrinsic defects in germanium. To this end monocrystalline Ge samples with various dopant types and concentrations are annealed at high temperature and rapidly cooled (quenched) to room temperature. The nature and concentration of defects in Ge produced in this way is studied with Fourier-Transform IR spectroscopy, Deep-Level Transient spectroscopy and Electron Paramagnetic resonance. In the course of this project a setup for infrared rapid thermal annealing and quenching of small samples was developed. Quenched-in defects were found to be mostly copper-related.

    This research has led to the PhD of dr. Siegfried Segers Study of point defects in monocrystalline germanium.

    Promoters: Freddy Callens, Eddy Simoen, Jan Vanhellemont, Henk Vrielinck

    Publications Siegfried Segers

    DLTS spectrum of samples quenched in silicone oil (tQ=60 min, TH=650°C; VR=-1V, VP =-0.2V, tW=512 ms) (a) experiment and (b) simulation. H1 and H4 have been identified as acceptor defect levels of substitutional Cu in Ge.

    Electrically active defects in group-IV and III-V semiconductors are still in the research focus of the group. Recently the focus has shifted towards compound or alloy group-IV materials (SiC, GeSn) and (In,Ga)As, and towards extended defects in these materials.

    Selected Publications

    Electrical activity of extended defects in relaxed InxGa1−xAs hetero-epitaxial layers

    1. Claeys, P.-C. Hsu, Y. Mols, H. Han, H. Bender, F. Seidel, P. Carolan, C. Merckling, A. Alian, N. Waldron, et al.


    Impact of band to band tunneling in In0.53Ga0.47As tunnel diodes on the deep level transient spectra

    S Gupta, Eddy Simoen (UGent) , R Loo, Q Smets, AS Verhulst, Johan Lauwaert (UGent) , Henk Vrielinck (UGent) and M Heyns

    (2018) APPLIED PHYSICS LETTERS. 113(23).

    Electrical properties of extended defects in strain relaxed GeSn

    Somya Gupta, Eddy Simoen (UGent) , Roger Loo, Yosuke Shimura, Clement Porret, Federica Gencarelli, Kristof Paredis, Hugo Bender, Johan Lauwaert (UGent) , Henk Vrielinck (UGent) , et al.

    (2018) APPLIED PHYSICS LETTERS. 113(2).