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Optical Characterization

Fig. 1: Setup for low-temperature photoluminescence measurements.

Optical characterization is a powerful method for understanding the properties of semiconductor materials and devices. At NaMLab, optical characterization is applied to determine defect types and energies, phonon energies and minority carrier lifetimes in semiconductor materials. Furthermore, the functionality and performance of photoactive devices are characterized with optical methods.

The optical laboratory at NaMLab is equipped with high resolution spectrometers and sensitive detectors for the ultraviolet (UV) to the near infrared (NIR) range. For excitation, different laser sources from UV (325 nm) to the visible range (514 nm) are available as well as broad band high-power light sources (Xenon lamps). This allows measuring the photoluminescence and excitation spectra of a large number of semiconductors. Additionally, the spectral response of photodiodes and solar cells can be investigated.

Fig. 2
CaptionFig. 2: Micro-Raman spatially resolved spectral map of semiconductor device structures.



The established methods at NaMLab include:

  • Low-temperature photoluminescence (15 – 300 K) in the UV – NIR range (340 nm – 1700 nm) with UV (325 nm) or VIS laser excitation
  • Spectral response with and without bias illumination for photosensors and solar cells
  • Micro-Raman with 457, 514 and 785 nm excitation wavelength (spatial resolution: 1 µm)
  • IR and VIS-NIR ellipsometry; VIS-NIR reflectometry
  • Microwave detected photoconductivity for 2D mapping of minority carrier lifetimes in silicon
Fig. 3: Photoluminescence spectrum of a 1 μm thick ultra-pure epitaxial GaN layer grown on a 2 μm thick MOCVD-GaN template. Characteristic photoluminescence peaks are indicated.


The potential of these techniques are highlighted in two examples:

  • Photomasks with array structures were characterized with Mueller Matrix spectroscopic ellipsometry as a function of the azimuth angle (Fig. 2). The intensity changes of the plot could be correlated to analytically determined Rayleigh singularities of different orders in transmission and reflection.
  • The material properties of epitaxially grown GaN are determined by photoluminescence at 15 K. Highly resolved excitonic emission lines reveal (compressive or tensile) stress and the impurity in corporation in GaN layers.


Contact: Dr. Andre Wachowiak, Dr. Walter Weber


NaMLab gGmbH
Nöthnitzer Str. 64 a
01187 Dresden

Phone: +49.351.21.24.990-00
Fax: +49.351.475.83.900

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