Photoluminescence excitation spectroscopy of GaAs:Er,O in the near-band-edge region

We report a spectroscopic study of GaAs:Er,O samples grown by metalorganic chemical vapor deposition, with excitation in the near-band-edge region, 1.22-1.62 eV. Photoluminescence under host-excitation is dominated by luminescence due to the Er-2O center (an erbium atom at a gallium site coupled with two adjacent oxygen atoms) in these samples. The characterization of different Er centers is demonstrated by the observation of I-4(15/3)-->I-4(11/2) intra-4f-shell transitions by photoluminescence excitation (PLE) spectroscopy. The transitions between these crystal-field-split 4f-shell levels are observed at similar to 1.26 eV (similar to 980 nm) which is at an energy attainable by PLE spectroscopy with a Ti:Sapphire laser. Two lines are assigned to the Er-2O center. This allows a semi-quantitative measurement of the relative concentrations of different centers to be made. PLE spectroscopy was also employed to study the trap levels related to the Er-2O center. However, we find no evidence for such a trap level in this energy range. The expected position of this trap is discussed in the light of these results and recent calculations. (C) 1996 American Institute of Physics.