We report transmission electron microscopy (TEM) studies of precipitation in Ag-implanted and annealedAl0.3Ga0.7As.Silver was chosen because it does not form compounds with Ga and/or As when precipitating based on bulk thermodynamics arguments. TEM confirmed the formation of an elemental metal/semiconductor composite, which consists of nanometer-sized Ag (fcc structure) precipitates dispersed in the matrix. The precipitates are nonspherical and have an orientation relationship toAl0.3Ga0.7Asof (200)Ag//(200)AlGaAs, (02-2)Ag//(02-2)AlGaAs, and [011]Ag//[011]AlGaAs. High temperature (900 °C) anneals transform the phase of the precipitate to hexagonal,Ag3(GaAl)compounds. This shape distribution has been correlated with inhomogeneous broadening of the optical absorption. ©1997 American Institute of Physics.