Deep-level symmetry studies using ballistic-phonon transmission in undoped semi-insulating GaAs

An anisotropic change in ballistic-phonon transmission induced by irradiation with 1.06-μm-wavelength photons has been measured in undoped semi-insulating GaAs. The anisotropy of the phonon transmission is consistent with scattering from a defect having trigonal symmetry. The metastability, as well as the thermal-annealing and optical-excitation properties of the observed change in phonon transmission, are consistent with those which have been associated with the dominant deep electronic level ($\mathrm{EL}2\mathrm{}$) in undoped semi-insulating GaAs.