Recent developments in phonoconductivity spectroscopy of shallow bound states in semiconductors

The phonon emission spectrum of a superconducting Al-junction contains a sharp quasi-monochromatic lineup to the range of Debye energies tuneable by the bias. This is evident from steep phonon-induced conduction (PIC) thresholds due to excitation of carriers in semiconductors from shallow bound states to the neighbouring band. Information on phonon coupling to carriers and phonon propagation at extremely high frequencies in superconductors and semiconductors can be obtained from such experiments