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Optical studies
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Optical characterization is an efficient way to determine material quality and purity, as well as to determine the bandgap of the CIGS alloy.
We use two separate setups dedicated to different wavelength domains. A setup dedicated to visible/UV is equipped with a DIGIKROM DK 240 monochromator covering the range 800 - 250nm, detection is performed with a HAMAMATSU 928 photomultiplier.
Excitation is performed using various lasers : from He/Ne (red) to 325nm He/Cd.
In the infrared domain, a HRS monochromator is fitted with a HAMAMATSU photomultiplier, cooled at 77K for the range 800 - 1600nm. in the 1600 - 2100 nm can be performed using an extended InGaAs photodiode.
The sample can be at room temperature, or mounted in an helium free closed loop cryostat, which allow to cool down the sample to 10K.
Transmission and reflectivity experiment can be performed using a white halogen lamp as excitation source. This allow for an easy evaluation of the bandgap, which in the case of CIGS translate into gallium composition.
Time resolved spectroscopy is performed using q-switched solid state red and green lasers at 655 and 532 nm. The signal is detected by a fast photodiode and sampled by a Gigasample/sec scilloscope. This simple setup allow us to investigate the nanosecond time domain, which is relevant for CIGS carrier lifetimes.
