The 1.681eV luminescence center which was characteristic of chemical vapor deposited film samples was studied in homo-epitaxially grown specimens. The present technique relaxed the strain which was typical of films which were grown onto hetero-substrates with lattice mismatch. It thereby markedly reduced the optical line-widths down to 0.0002eV. The no-phonon luminescence transition exhibited a fine structure that consisted of a fully-resolved doublet with line components at 1.6820 and 1.6828eV. The doublet thermalized with an activation energy of 0.0008eV; equal to a spectroscopic spacing of 0.0008eV. In addition, each doublet component comprised an associated close satellite in a mirror-like arrangement. Three other partly-resolved lines increased the total number of components in the no-phonon transition to at least 7. Photoluminescence and photoluminescence excitation measurements which were performed under uniaxial stressing along <001> revealed a splitting of the no-phonon structure into 4 main components. These were studied at various temperatures and stress levels. An electronic level scheme was developed which involved 2 excited states from which electrons radiatively relaxed to 2 lower states. The data were not consistent with excitonic recombination or with electron-to-hole recombination. They indicated that the optical center was subjected to a uniaxial internal over-pressure of some 0.06GPa; due probably to its large size. The luminescence decay time of the optical center was found to be between 4ns (5K) and 2.7ns (300K) in the homo-epitaxial film and was approximately equal to unity, regardless of the temperature, in polycrystalline films.

H.Sternschulte, K.Thonke, R.Sauer, P.C.Münzinger, P.Michler: Physical Review B, 1994, 50[19], 14554-60