NATURE OF MG IMPURITIES IN GAN

Mg doped GaN epilayers grown by reactive molecular beam epitaxy (ME) e xhibit clear persistent photoconductivity (PPC) whose manifestation ha s been used to probe the nature of Mg impurities in GaN. PPC buildup a nd decay transients and the dependence of the PPC decay time constant on the PPC buildup time have been systematically measured and formulat ed in the context of lattice relaxed Mg impurities (or AX centers). Ou r results have demonstrated that there is an energy barrier of about 1 29 meV which prevents free hole capture by ionized Mg impurities and t hat there is a lattice relaxation associated with Mg impurities in GaN . We also present a detailed comparison for Mg impurities in p-type Ga N epilayers grown by MBE (hydrogen-free) and metalorganic chemical dep osition (hydrogen rich). (C) 1996 American Institute of Physics.