Emission mechanism of the yellow luminescence in undoped GaN

The temperature-dependent behavior of the yellow-band (YB) luminescence in n-type GaN epitaxial layers grown by metalorganic chemical-vapor deposition have been investigated. The YB luminescence peak position initially shows a blueshift in the temperature range from 5 to 40 K and then a redshift in the temperature range from 40 to 280 K. The temperature dependence of the p eak intensity, as well as the integrated intensity. also shows an abrupt ch ange at 40 K. above which the intensities increase with the temperature unt il they reach a maximum value at around 120 K and then decrease monotonical ly. The optical absorption spectrum associated with the transition related with the YB luminescence was observed at temperatures around 100 K and 150 K at which the intensity of the luminescence approached maximum values. Acc ording to the Lucovsky theory, the optical absorption related to the YB is best described by a transition from an impurity level to the conduction ban d. This result indicates that the YB luminescence is due to a transition fr om shallow to deep donor states.