Although considerable progress has been made in, reducing background impurities and controlling optical and electronic properties of heteroepitaxial GaN layers over the last three decades, strong experimental evidence that clarifies the chemical identify of the shallow donors has been presented only recently. Variable temperature photoluminescence studies of recombination processes associated with excitons bound to donors and Fourier transform infrared (FTIR) measurements of donor absorption in hydride-vapor-phase epitaxial GaN are presented. PL studies of undoped and Si-doped homoepitaxial layers are consistent with and support the identification of Si and 0 as the dominants pervasive shallow donors in GaN, as measured by FTIR-and secondary ion mass spectroscopy. Analyses of the two-electron satellite (2ES) transitions reveal the observation of a number of transitions associated with ground and excited states of both the donors and the donor-bound exciton complexes. All the, 2ES lines observed in this work can be accounted for by recombination of excitons bound to Si and 0 donors and line positions are in excellent agreement with the energies of donor intraimpurity transitions measured previously by infrared absorption. (C) 2002 Elsevier Science B.V. All rights reserved.