Impact of the growth polar direction on the optical properties of GaN films grown by metalorganic vapor phase epitaxy

The growth polar direction during metalorganic chemical vapor phase epitaxy of wurtzite GaN films was shown to affect the optical properties an terms of impurity and vacancy-type defect incorporation during the growth. The GaN film grown towards the Gaface (0001) (+c polarity) exhibited clear excitonic features in its optical absorption and luminescence spectra up to room temperature. Conversely, the film with the N-face (000-1) (-c polarity) exhibited a broad emission band, which is located in the broadened absorption tail. The Stokes shift remained even at 300 K. The difference between the two was explained in terms of the presence of impurity-induced band tail states in -c GaN due to increased impurity density and enhanced incorporation of large volume vacancy-type defects, which were confirmed by secondary ion mass spectrometry [Sumiya et al., Appl. Phys. Lett. 76, 2098 (2000)] and monoenergetic slow positron annihilation technique.