Ballistic phonon transmission across wafer-bonded crystals

Abstract

We have studied phonon transmission through wafer-bonded GaAs–GaAs interfaces using the techniques of phonon imaging. The short wavelength phonons used for imaging (λ≈10 nm ) are an extremely sensitive probe of the bond. We report unprecedented transmission of phonons through carefully prepared bonds. This transmission is remarkable since strong phononscattering is usually observed at virtually any free surface. The dramatic differences between phonon transmission through well bonded interfaces and phonon transmission through poorly bonded interfaces are the basis of an easily determined quality factor of the bond. In contrast to electron microscopy, the phonon measurements of bond quality are not destructive.