INFRARED-ABSORPTION STUDIES OF THE BORON B(2) CENTER IN GAAS

The B(2) local vibrational modes (LVM) at 601 cm** minus **1 and 628 cm** minus **1 are often observed in electron irradiated LEC GaAs crystals and have been attributed both to boron on the arsenic site and to interstitial boron. These local vibrational modes are studied in infrared transmission at high resolution (0. 04 cm** minus **1) at temperatures near 4. 2 K. The strength of the B(2) LVM absorption increases linearly with electron irradiation with zero intercept at zero fluence irrespective of the position of the Fermi level. A splitting of the B(2) LVM attributed to the isotope distribution of gallium nearest neighbors is observed. The results imply that the B(2) centers are boron with gallium nearest neighbors in tetrahedral symmetry and that the B(2) centers are not present in the as-grown crystals but are produced by electron irradiation. We conclude that B(2) is not the commonly-found 78 mev acceptor.