Observation of Metastable and Stable Energy Levels of EL2 in   Semi-insulating GaAs
  By using combination of detailed experimental studies, we identify the metastable and stable energy levels of EL2 in semi-insulating GaAs. These results are discussed in the light of the recently proposed models for stable and metastable configurations of EL2 in GaAs. 
D. Kabiraj and Subhasis Ghosh