AlN bandgap temperature dependence from its optical properties

In the present work we report on the AlN gap energy temperature dependence studied through the optical properties of high-quality large bulk AlN single crystals grown by a sublimation–recondensation technique. The cathodoluminescence, transmission/absorption as well as optical reflectance measurements at low temperature show a clear feature at about 6.03 eV, which could be attributed to the free exciton A. Even using a rather thick sample it was possible to observe the absorption due to the free exciton A in this energy range due to its large binding energy. We followed the temperature evolution of these features up to room temperature and inferred the gap energy temperature dependence using the exciton binding energy obtained by our group in the past.