Ballistic phonon transmission across wafer-bonded crystals

We have studied phonon transmission through wafer-bonded GaAs-GaAs interfac es using the techniques of phonon imaging. The short wavelength phonons use d for imaging (lambda approximate to 10 nm) are an extremely sensitive prob e of the bond. We report unprecedented transmission of phonons through care fully prepared bonds. This transmission is remarkable since strong phonon s cattering is usually observed at virtually any free surface. The dramatic d ifferences between phonon transmission through well bonded interfaces and p honon transmission through poorly bonded interfaces are the basis of an eas ily determined quality factor of the bond. In contrast to electron microsco py, the phonon measurements of bond quality are not destructive. (C) 1999 A merican Institute of Physics. [S0003-6951(99)00205-3].