A new center related to ${\mathrm{As}}_{\mathrm{Ga}}$ has been found at relatively high concentrations (${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$) in semi-insulating (2×${10}^7$ Ω cm) molecular beam epitaxial GaAs grown at 400 °C. Although the ir photoquenching and thermal recovery characteristics are nearly identical to those of EL2, the thermal activation energy is only 0.65±0.01 eV, much lower than the EL2 value of 0.75±0.01 eV. Other properties which are different include the electron-capture barrier energy, hyperfine constant, and magnetic circular dichroism spectrum.

• Received 20 July 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.465