The properties of Si donors in hetero-epitaxial layers were investigated. The n-type layers were grown by metalorganic chemical vapor deposition, and were either unintentionally doped, or intentionally doped with Si. The samples were investigated by means of variable-temperature Hall effect measurements, and photoluminescence spectroscopy. In both types of sample, the n-type conductivity was found to be dominated by a donor with an activation energy of between 0.012 and 0.017eV. This donor was attributed to Si atoms, SiGa, which substituted for Ga in the lattice. The range of activation energies was attributed to various levels of donor concentrations and to acceptor compensation. The photoluminescence signature was attributed to a donor-acceptor pair recombination which involved the Si donor level as the initial state of the radiative transition. This revealed that the optical Si donor level in the band-gap was located at about Ec - 0.022eV. A deeper donor level was also present; with an activation energy of about 0.034eV. It was attributed to O donors, ON, which substituted for N.

W.Götz, N.M.Johnson, C.Chen, H.Liu, C.Kuo, W.Imler: Applied Physics Letters, 1996, 68[22], 3144-6