Asymmetry of photostimulated exoemission in ferroelectrics

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Abstract
It is shown that photostimulated exoemission in ferroelectrics is substantially asymmetric. Asymmetry is exhibited in the dependence of emission current on the direction of the crystal polar axis. Consideration is given to the nature of the phenomenon of emission asymmetry which is determined by two factors: a) bending of zones having opposite signs arising near the polar cuts as a result of the screening of the spontaneous induction field; b) existence of asymmetric periodic potential in an acentric polar crystal. The asymmetry parameters have been measured by registering the orientational and spectral dependences of the photoemission quantum yield. The possibility is shown of studying the asymmetry of elementary electronic processes in ferroelectric LiNbO3:Fe excited by light which does not produce an extrinsic photoeffect, but induces on the crystal surface a photovoltaic field with an intensity of 106 V.cm−1. The emission current proceeding from the cut perpendicular to the positive direction of the polar axis is of field nature. The energy of emitted electrons corresponds to the photovoltaic potential.