Mode-selective scattering of phonons in a semi-insulating GaAs crystal: A case study using phonon imaging

Using a slotted-crystal geometry, phonon-imaging techniques, and Monte Carlo simulations, we have measured the absolute scattering rates of longitudinal and transverse phonons with frequency higher than 0.7 THz in undoped GaAs at T=1.6 K. Comparisons are made to the theoretical rate constant, ${\mathit{A}}_0$=7.38×${10}^{\mathrm{-}42}$ ${\mathrm{s}}^3$, for mass-defect scattering from naturally occurring isotopes in GaAs. The scattering of longitudinal phonons is found to be consistent with isotope scattering with the rate constant ${\mathit{A}}_{\mathrm{L}}$≤1.3${\mathit{A}}_0$; however, the transverse-phonon scattering is much stronger, yielding the rate constant ${\mathit{A}}_{\mathrm{T}}$=(4.0±0.7)${\mathit{A}}_0$. This mode-selective scattering is inconsistent with simple elastic scattering from mass defects.