Energy-Resolved Measurements of the Phonon-Ionization of $D^{-}$ and $A^{+}$ Centers in Silicon with Superconducting-Al Tunnel Junctions

By means of phonon spectroscopy with superconducting-Al tunnel junctions as tunable phonon generators we show that the threshold energy of the phonon-induced conductivity for Si: ${\mathrm{B}}^{+}$ and Si: ${\mathrm{P}}^{-}$ agrees well with far-infrared data, proving that the ionization is mainly a one-phonon process. This ionization mechanism allows a sensitive detection of very-high-frequency phonons.