Research

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 Si, Ge, diamond, III-V, II-VI and Cu(In/Ga)Se2, with applications in 

  • Microelectronics
  • Optoelectronics
  • Photovoltaics (solar cells).

Defects are investigated trough their electronic and vibrational (local vibrational modes (LVM)) and electron magnetic resonance spectra.

We aim at obtaining physical properties, structural identification and quantification of defects via various electrical characterization and (quasi) spectroscopic techniques. Special attention is given to defect determination at the edge of the detection limits. 

The characterization techniques that are used are

  • Electron paramagnetic resonance (EPR, in collaboration with the EMR group)
  • Fourier-transform infrared spectroscopy (FTIR)
  • Deep-level transient spectroscopy (DLTS).

Research topics

  • Characterization of defects in group IV semiconductors
  • Electric and optical characterization of thin-film solar cells
  • Detection and identification of shallow- and semi-shallow- level defects in semiconductors
  • Optical properties of absorber layers in thin-film solar cells
  • Vibrational mode study of Metal-Organic Frameworks in Mid- and Far-IR

Running/recent projects

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

    Abstract
    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)

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

    Abstract
    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.


    Publications
  • Identification of electrically active defects in materials for solar cells

    Abstract
    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).


    Publications