Continuous high-resolution phonon spectroscopy up to 12 meV: Measurement of theA+binding energies in silicon

We have measured the binding energies of ${\mathrm{Ga}}^{+}$, ${\mathrm{Al}}^{+}$, and ${\mathrm{In}}^{+}$ centers in silicon with energy-resolved phonon-induced electrical conductivity. For ${\mathrm{Ga}}^{+}$ and ${\mathrm{Al}}^{+}$ we obtain the value of about 2 meV as earlier found for ${\mathrm{B}}^{+}$, whereas the binding energy of ${\mathrm{In}}^{+}$ is 6 meV. Spectral structures attributed to impurity interactions found for higher concentrations of In at energies up to about 12 meV demonstrate that acoustic phonons up to this energy are transmitted from the tunnel junction to the substrate.