DiSC (Defects in SemiConductors)

Facilities

Fourier Transform Infrared spectroscopy (FT-IR)

FT-IR VERTEX 80v + Hyperion 2000

This facility was realized through a Hercules-1 project: FT-IMAGER, a wide-range multi-purpose Fourier-Transform Infrared facility for Materials, Archaeological and GEological Research. Information on the consortium behind this project and recent research results can be found on this site.

Basic instruments

  • BRUKER Vertex 80v vacuum wide-range multi-purpose FT-IR spectrometer, with spectral range between 15000 and 10 cm-1 (near- to far-IR)
  • Hyperion 2000 microscope in the near, mid and far IR

Peripheral equipment

  • Liquid helium cryostats for mid and far IR region: contact gas and cold finger
  • Home-built vacuum sample compartment for photoluminescence extension

Measurement modes

  • Transmission – Specular Reflection - Attenuated total reflection (ATR)
  • Photothermal ionization spectroscopy (PTIS)
  • Photoluminescence

Recent publications

Deep level transient spectroscopy (DLTS)

The following services with different measurement modes are possible for deep level transient spectroscopy.

Basic instruments

  • PhysTech Fourier Transform DLTS equipped with liquid He/liquid N2 crystats (4-600 K) and Leybold temperature controller
  • Agilent fast pulse generator (pulse length >1 ns) for fast electrical filling pulses
  • Laser diodes (900 nm and 1500 nm) for optical filling pulses

Measurement modes

  • DLTS: classical capacitance DLTS using electrical pulse (voltage range +/-100 V)
  • CC-DLTS: constant capacitance DLTS
  • ODLTS: capacitance DLTS using optical pulse
  • CDLTS: current DLTS using optical or electrical pulse
  • QDLTS: charge DLTS

Topics with selected papers

Electron Paramagnetic Resonance (EPR)

Spectroscopy at microwave frequencies is complicated by the narrow bandwidth of microwave components. Moreover, in EPR resonance cavities are used as microwave amplified, fixing the measurement frequency for every specific sample. In EPR spectroscopy this difficulty is easily overcome, since the separation of energy levels can be changed conveniently by varying the strength of an externally applied magnetic field. For this reason electron magnetic resonance experiments are typically performed at a single microwave frequency, and a spectrum is recorded as magnetic field sweeps. The spectrometers in our lab use a single microwave frequency of 9.5 GHz (X-band) and 34.0 GHz (Q-band).

The possibility to record spectra at different microwave frequencies is a great asset in EPR spectroscopy. Sometimes, having spectra at several microwave frequencies is even indispensable for unambiguous spectrum interpretation. It allows to separate field-dependent (e.g. electron and nuclear Zeeman interaction) from field-independent interactions (hyperfine, zero-field splitting) in the spin-Hamiltonian of detected paramagnetic centers. High-spin centers with large zero-field splitting may even require high-frequency EPR (≥ 94 GHz) and large magnetic fields (several Tesla) for detection of the EPR-allowed transitions. On the other hand, high-frequency EPR requires superconducting magnets and is difficult to operate (small microwave components, samples and sample holders). The intermediate Q-band frequency presents a nice compromise, combining the ease of operation of standard EPR (at X-band) with an already improved sensitivity and g-factor resolution, and increased detectabilty for centers with large zero-field splitting (compared to X-band).


In favor of the highest frequency, there is increased sensitivity, minimization of higher order effects, improved resolution, and spectroscopy between levels whose zero field splitting is of the order of the microwave quantum.

  • Q-band EPR/ENDOR (Bruker Elexsys E500)
    The frequency range is 33.8 GHz - 34.1 GHz. Microwave power: 160 mW and maximum magnetic field value: 1.5 T.
    Temp range 3 - 300 K
    In situ illumination possible
  • X-band EPR/ENDOR (Bruker ESP300E)
    The frequency range is 9.5 GHz - 9.8 GHz. Microwave power: 200 mW and maximum magnetic field value: 1.0 T.
    Temp range 3 - 300 K (regular cavity) and 300 - 1273 K (cylindrical cavity)
    In situ illumination possible
  • X-band EPR (Varian E-line)
    The frequency range is 8.87 GHz - 9.65 GHz. Microwave power: 200 mW and maximum magnetic field value: 0.9T
    Temp range 3 - 300 K
    Dual cavity

EPR magnets

Left picture: Q-band setup, middle: X-band EPR/ENDOR, right picture: X-band EPR

Topics with selected papers

Other electrical characterisation

Hall - Van der Pauw setup

The Van der Pauw method makes it possible to precisely determine the electrical resistivity of a material by means of 4 contact points. Two contact points apply a well known current to the material, the other two measure the voltage across the material. This technique has the advantage to cancel out contact resistance on the measurement result. The same setup could also be used to measure Hall voltage.

Hall - Van der Pauw

Minority carrier lifetime measurement

The lifetime of minority charge carriers can be measured using contact and non-contact methods.

All requests for DLTS, FTIR and EMR measurements may be addressed directly to and will be evaluated on an individual basis.