On the origin of the 265 nm absorption band in AlN bulk crystals

Single crystal AlN provides a native substrate for Al-rich AlGaN that is needed for the development of efficient deep ultraviolet light emitting and laser diodes. An absorption band centered around 4.7 eV (similar to 265 nm) with an absorption coefficient above 1000 cm(-1) is observed in these substrates. Based on density functional theory calculations, substitutional carbon on the nitrogen site introduces absorption at this energy. A series of single crystalline wafers were used to demonstrate that this absorption band linearly increased with carbon, strongly supporting the model that C-N(-) is the predominant state for carbon in AlN. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4717623]