Optical metastability in undoped GaN grown on Ga-rich GaN buffer layers

Investigations on defect-related optical metastability in undoped GaN epilayers grown on GaN buffer layers are presented. The III/V ratio in the buffer layer was varied over a range such that the resistivity of the GaN epilayers traversed a semiconducting to semi-insulating transition. The high-resistive and semi-insulating GaN epilayers show photo induced metastability, which is revealed through a number of features: (i) the intensity of the blue luminescence band decreases as the intensity of the yellow luminescence band increases; (ii) quenching of photocurrent; and (iii) persistent photoconductivity, under the illumination of a low-power ultraviolet laser. It has been shown that these unwanted transient effects can be eliminated in the GaN epilayers by reducing the III/V ratio in the buffer layer. A qualitative discussion of these results suggests that the metastable defects, which are associated with both yellow and blue luminescence bands, may have important consequences for our understanding of defect-related luminescence in GaN. (C) 2002 American Institute of Physics.