Infrared absorption in indium nitride

The room-temperature optical absorption spectra of indium nitride films in the subband-gap energy range 40 meV to 2.0 eV are surveyed. The major features are two broad absorption bands: a band-edge tail with a threshold energy of about 1 eV and a broad peak centered at about 0.3 eV. Both are strongly sample dependent and are identified with crystal defects associated with the observed electrical compensation of the shallow donor impurity. All samples show optical excitation of the 50–60-meV shallow donor seen in thermal excitation measurements, while some exhibit an absorption doublet, whose nature is not understood, around 0.15 eV.