Spectral oscillations of photoconductivity

Abstract

Interaction of photoexcited carriers with optical phonons can produce oscillations in the spectrum of photoconductivity. The separation between successive minima is related to the phonon energy. The oscillation occurs when the excited carriers lose their energy rapidly by the emission of optical phonons and do not exchange energy with acoustical phonons effectively during their lifetime. Under such conditions, the energy distribution of carriers varies with photon energy periodically within the range of one optical phonon energy from the edge of the energy band, leading to a variation of photoconductivity either through an energy dependence of the carrier mobility or through an energy dependence of the carrier lifetime. Oscillations of this nature have been observed in a variety of semiconductors and have been found in intrinsic as well as extrinsic photoconductivity and photomagnetic effect. Studies of the oscillations have provided information on the energy band, excitons, impurity levels and phonon energy. Under high magnetic fields, additional structures in the spectrum can be observed which are associated with the Landau levels. The effect provides an additional means for the study of Landau levels and quantum transport.