Experimental setup

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PR measurements are performed at near normal incidence in the 0.7-1.8 eV range, with energy steps and spectral resolution of 1 meV. The standard experimental apparatus operates with the monochromatized light of a 100 W halogen lamp as probe source. The excitation source (PR) is provided by a 2 mW He-Ne laser, mechanically chopped at 220 Hz.

The sample is mounted in thermal contact with the cold finger of a micro-miniature Joule-Thompson refrigerator coupled with a programmable temperature controller that allows measurements in the 80-300 K temperature range and provides the thermal modulation (ΔT ~ 2 K at 0.1 Hz) for TR measurements. With an appropriate sample holder and a function generator to supply the a.c. voltage, ER measurements can be performed in the same temperature range.