energy-difference between the valence and conduction bands (bandgap), and is hence lower in energy than the excitation photon, so that the emission is red-shifted with respect to the excitation light. At low temperatures, a PL peak is quite sharp. As the temperature increases, the peak broadens and shifts to lower energy. This red-shift, typical for such materials, indicates bandgap Introduction Temperature-dependent photoluminescence (PL) spectroscopy is a powerful optical method for characterizing materials. PL can be used to identify defects and impurities in Si and III-V semiconductors, as well as determine semiconductor bandgaps. At room temperature, PL emission is usually broad—up to 100 nm in width. When samples are cooled, structural details may be resolved; a small

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