Measurements of the nonradiative states of optically illuminated semiconductors by a superconducting tunnel junction

A novel technique which utilizes a superconducting tunnel junction as a phonon detector is introduced to detect nonequilibrium phonons from the nonradiative states in optically illuminated semiconductors such as Si or GaAs. The method proved to have very high sensitivity for phonon detection with a large S/N ratio. The detected phonon signal as a function of wavelength of the light for GaAs exhibited modulated structures below the band-gap energy consistent with the presence of an EL2 level.