Cathodoluminescence measurements were performed for carbon doped and undoped aluminum nitride thin films in the temperature range from liquid helium to room temperature. The AlN films were grown on three different substrates: 6H–SiC, 4H–SiC, and sapphire. From these samples, a strong luminescence peak surrounded by two weaker peaks in the near band-edge region, near 6 eV, was observed. For AlN on sapphire, this near band-edge transition can be further resolved into three peaks at 6.11, 5.92, and 5.82 eV. These peaks are believed to be due to exciton recombination. The effects of substrate materials and carbon doping on the exciton peak were discussed. The temperature dependence of the peak position and line width of this transition was also studied. The temperature coefficient of the band-gap energy is estimated to be 0.51 meV/K. © 1998 American Institute of Physics.