The bulk photovoltaic effect of photorefractive :Fe crystals at high light intensities

Abstract

Direct measurements of the bulk photovoltaic current density in photorefractive and crystals were performed at high light intensities. Illumination of the crystals with light pulses of a Q-switched frequency-doubled Nd:YAG laser (pulse duration 20 ns; light wavelength 532 nm) yielded a photovoltaic current through the crystals which charged a capacitor. Afterwards an electrometer measured the voltage of the charged capacitor. From this voltage and from capacity and exposure time the current density was deduced. For intensities above a contribution to which increased quadratically with light intensity I appeared for crystals. Co-doping with Mg and Zn lowered the quadratic component. Our results are in good qualitative and quantitative agreement with previous holographic measurements and support the claim that the intrinsic defect acts as a secondary photorefractive centre in at high light intensities.

Comparative Study of Composition Dependences of Photorefractive and Related Effects in LiNbO3and LiTaO3Crystals

“…In LiTaO 3 it may be caused, similar to well-established findings in LiNbO 3 [3,4] . The excitation wavelength was 632.8 nm with a power of about 2 mW, corresponding to high-intensity excitation regime as a confocal microscope with microscope objective × 100 was used to excite and to collect the luminescence emission.…”

“…Recently, a new interest to LiNbO 3 and LiTaO 3 crystals was stimulated by the study of small polarons and bipolarons [1][2][3][4][5]. Besides of fundamental aspects, polarons are very perspective entities for practical purposes.…”

“…Polaron states can be used in two-color holography as intrinsic photorefractive centers in chemically reduced crystals [6,7]. At the same time, suppression of the photorefractive damage, known to be the main limiting factor for a variety of highthroughput applications of nominally pure LiNbO 3 and LiTaO 3 crystals [1,2], necessarily requires a detailed knowledge of light-induced charge transport governed by polarons related to the particular intrinsic defects [1][2][3][4][5][6][7]. These practical aspects mentioned above require some new effective method for quantitative evaluation of such intrinsic defects.…”

Short-circuit photocurrent in epitaxial lead zirconate-titanate thin films

“…11,12 It is worth noting that these materials also show a significant photorefractive effect. 12,13 Bulk photovoltaic effect consists in the generation of large voltages under homogeneous illumination with UV light. These voltages are usually much larger than the band gap of the material, which is in the range of 3 -4 eV for the ferroelectric oxides with perovskite structure.…”

Photovoltaic effect in a wide-area semiconductor-ferroelectric device

“…Semiconducting ferroelectrics would be potentially interesting photovoltaics, provided that the bandgap is small relative to available solar energies. 6,7 Multiferroic BiFeO 3 (BFO) has been shown to have a low bandgap ($2.7 eV) and comparatively good sunlight response; in general, advances in the fabrication, bandgap engineering, and characterization of ferroelectric thin films make it possible to observe very high white-light photo-response in ferroelectric thin films and bulk. [8][9][10] Semiconductor ferroelectric photo-voltaics (SFPV) show a diode effect associated with the direction of bulk electric polarization which switches its direction when the electric polarization is flipped by an external voltage.…”