Non-steady-state photoelectromotive force in the wide-band-gap dielectric MnO

Although manganese oxide is a wide-band-gap dielectric with a band gap $E_g\backsimeq$ 4 eV and, in the undoped state, is characterized by a high electrical resistivity, it has been found experimentally that there is a non-steady-state photoelectromotive force in dynamic space-charge gratings formed in MnO by light with a photon energy of 1.96 eV ($\lambda$ = 633 nm). The dependences of the photoelectromotive force signal amplitude on the phase modulation frequency, light intensity, and spatial frequency of the interference pattern have been investigated. The unusual frequency dependence of the signal has been explained in terms of the two-level semiconductor model taking into account the presence of shallow traps in the crystal. The photoelectric parameters of the material have been determined.