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Research Area - Nitrides

Optical Characterisation

Optical spectroscopic techniques are powerful, non-destructive tools for studying properties of semiconductor materials, such as fundamental parameters (bandgaps, dielectric constants optical transition probabilities), elementary excitations (excitons, polaritons, plasmons, phonons), extrinsic and intrinsic defects, internal strain and electric fields etc. Optical spectroscopy is generally based on a measurement of the spectral dependence of the optical response of the material after an excitation (optical, electron, ion, thermal etc).

In our Semiconductor Materials group the main techniques we are using is photoluminescence (PL) spectroscopy. We have several fully equipped set-up for carrying out the conventional PL, PL excitation (PLE), polarization-resolved PL, magneto-PL (up to 14 T), micro-PL (with space resolution < 2 mm), and time-resolved PL (TRPL) (with time response < 50 ps). The studied samples are optically excited by discrete laser lines or tunable lasers (in continuous wave, picosecond, or femtosecond modes) in spectral range 266 – 1350 nm. For detection of the PL spectra charge-coupled devices (CCDs), photomultiplier tubes (PMTs) or photovoltaic detectors covering a spectral range from deep ultraviolet (DUV) to mid-infrared (MIR) are used. All measurements are performed in variable-temperature cryostats in temperature range 2-300 K.   Other techniques we are applying are: Raman spectroscopy (RS), Fourier Transform Infrared ( FTIR) spectroscopy , Scanned Near-field Optical Microscopy (SNOM), cathodoluminescence (CL), and spectroscopic ellipsometry (SE).   Our research covers optical properties of GaN and InN epitaxial layers, bulk GaN, InGaN/GaN and AlGaN/GaN heterostructures as well as low-dimensional structures – quantum wells (QWs) and superlattices (SLs). The recent and ongoing projects we are working include:

  • Electronic structure and recombination dynamics of free and donor-bound excitons in GaN (P. P. Paskov, J. P. Bergman, B. Monemar)
  • Mg-related acceptors in polar and nonpolar homoepitaxial GaN layers grown by MOCVD, MBE and HVPE (B. Monemar P. P. Paskov, G. Pozina, C. Hemmingsson J. P. Bergman)
  • Optical signatures of extended structural defects in nonpolar and semipolar GaN layers grown on different substrates by different lateral overgrowth techniques (P. P. Paskov, B. Monemar)
  • Effect of the surface potential and depletion field in GaN/AlGaN and InGaN/GaN QW structures (G. Pozina, B. Monemar, P. P. Paskov)
  • Emission properties of nonpolar and semipolar InGaN/GaN QW structures grown on bulk GaN substrates (P. P. Paskov, B. Monemar)
  • Phonon modes and strain anisotropy in nonpolar GaN and InN layers studied by generalized infrared spectroscopic ellipsometry (V. Darakchieva, B. Monemar) '
  • Electron accumulation at polar and nonpolar surfaces of InN (V. Darakchieva, B. Monemar)

Responsible for this page: Fredrik Karlsson
Last updated: 04/17/13