Theory of photovoltaic effects in crystals without an inversion center

Photon mechanisms of the shift and ballistic linear photovoltaic effects in semiconductors with a degenerate valence band are investigated theoretically. These mechanisms are attributed both to real-space hole shift in direct optical transitions between branches of the valence band and to the asymmetry of electron-phonon interaction, with allowance for Frölich electronphonon interaction. The temperature and frequency dependences of the photocurrent are determined, and the results are compared with experimental data for p-type GaAs. The light absorption coefficient, the current due to entrainment of electrons by photons, and the shift linear photovoltaic (LPV) effect, all associated with direct optical transitions accompanied by electron spin flip, are calculated for crystals without an inversion center. Allowance is made for the contribution to the entrainment current from inclusion of the wave vector in the energy conservation law and in the momentum conservation law and for the interaction of the magnetic field of the light wave with the electron magnetic moment. The contribution of “isotropization” of the photocarrier distribution function to the shift LPV current in semiconductors with a complex valence band is calculated. It is shown that the scattering of photocarriers by LO-phonons in each stage of the cascade scattering process yields a current contribution.

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