FINE STRUCTURE OF THE 3.42 eV EMISSION BAND IN GaN

A luminescence band centered around 3.42 eV is commonly observed in GaN. Its appearance has been tentatively assigned to an oxygen donor level. Stimulated laser activity has also been reported at this energy. We present a study of this band in GaN grown by high temperature vapor phase epitaxy (HTVPE). The high quality of this material, with an excitonic line width as narrow as 3 meV, allows us to distingish four different peak positions of this luminescence band. They appear at 3.4066, 3.4121, 3.4186, and 3.4238 eV (T = 6 K). Within the experimental error the lines exhibit an equidistant spacing of 6 meV. They show a pressure behavior similar to shallow levels described by effective mass theory. We discuss our results in the context of incorporation of oxygen and structural defects in GaN