Optical absorption of GaN thin films shows previously unreported structure at 3.8 eV, which is interpreted as the excitonic "knee" due to transitions across the fundamental direct energy gap previously thought to occur at an energy of about 3.4 eV. We also give the first report of the specular reflectance of GaN; peaks were observed at 6.8, 9.5, and 10.7 eV.

• Received 17 April 1970

DOI:https://doi.org/10.1103/PhysRevLett.24.1421