A low-symmetry interstitial boron centre in irradiated gallium arsenide

Irradiation of boron doped gallium arsenide by either 2 MeV electrons or fast neutrons leads to the production of a defect centre involving a single boron atom. The defect has localised vibrational modes at 763 cm -1 , 641 cm -1 and 371 cm -1 for 11 B and correspondingly higher frequencies for 10 B. The centre, previously labelled as B(1), is considered to be due to a bonded boron interstitial atom with lower than axial symmetry. The defect anneals at about 200 degrees C. Absorption from a similar defect in GaP has been reported and discussed previously but the lower frequency vibrational modes are masked by two-phonon absorption features in that host.