Various nuclear transmutation methods were used to study the effects of Cu doping. In one method, as-grown material was irradiated with thermal neutrons. After thermal annealing, this resulted in the incorporation of CuZn centers. It was suggested that these observations were consistent with isolated CuZn centers being involved in Cu red and green emissions but not in I1d excitonic emission. In the case of a second method, it was shown that Zn annealing could be effectively used in investigations that involved the irradiation of as-grown material. This was because the Zn annealing treatment significantly reduced background photoluminescence emissions from bulk samples. A third technique involved homo-epitaxial layer growth from previously irradiated sources. The epitaxial layers exhibited no predominant I1d excitonic emission, and a very low level of deep emissions. Because Cu atoms were introduced here at Zn sites after crystal growth, the Cu atoms were unable to interact with other dopants or with lattice defects. The absence of interactions during crystal growth permitted the unambiguous incorporation, far from equilibrium, of isolated CuZn centers.

E.D.Wheeler, J.L.Boone, J.W.Farmer, H.R.Chandrasekhar: Journal of the Physics and Chemistry of Solids, 1997, 58[1], 79-84