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

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Abstract
The growth polar direction during metalorganic vapor phase epitaxy of wurtzite GaN was shown to affect the optical properties in terms of impurity and vacancy incorporation during the growth. The GaN film grown toward the Ga (0001) face (+c polarity) exhibited clear excitonic features in its optical absorption and luminescence spectra up to room temperature. Conversely, the film with the N (0001̄) face (−c polarity) exhibited a broad emission band, which locates in the broad absorption tail. 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 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.