Photoconductivity and photoconversion at a photorefractive thin crystal plate Jaime Frejlich a , Ivan de Oliveira b,⇑ , William R. de Araujo c , Jesiel F. Carvalho d , Renata Montenegro d , Marc Georges e , Karl Fleury-Frenette e a Instituto de Física ‘‘Gleb Wataghin”/UNICAMP, Campinas, Brazil b Laboratório de Óptica, Faculdade de Tecnologia/UNICAMP, Limeira, SP, Brazil c Laboratório Nacional de Luz Síncrotron, Campinas, SP, Brazil d Instituto de Física, Universidade Federal de Goiás, Goiânia, GO, Brazil e Centre Spatial de Liège, Université de Liège, Belgium article info Article history: Received 8 December 2015 Received in revised form 23 February 2016 Accepted 24 February 2016 Available online xxxx Keywords: Photoconductivity Photorefractive materials Optoelectronics abstract We report on the photoconductivity and the photoelectric conversion measured on a thin photorefractive sillenite crystal plate, between transparent electrodes, in the longitudinal configuration where the current is measured along the same direction of the light beam through the sample. Its behavior is based on the already reported light-induced Schottky effect. The wavelength for optimal photoconductivity is determined. A specific parameter is formulated here for quantitatively determining the photoelectric conversion efficiency of the sandwiched material. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Photorefractive materials are photoconductive and electro- optics and are particularly suited for almost real-time reversible optical recording by transforming a spatially modulated illumina- tion into a corresponding volume index-of-refraction modulation that can be read using an auxiliary probe beam [1–3]. These mate- rials are also useful as high capacity volume memories [4–7], optical components fabrication [8] and for mechanical vibration modes detection in 2D [9,10] and various nondestructive metrol- ogy applications [11]. In this paper we shall focus only on the pho- toconductive properties and photoelectric conversion performance of photorefractive Bi 12 TiO 20 crystal. Light-induced Schottky effect at a transparent conductive electrode-bulk photorefractive crystal interface was already reported [12] before and shown to be due to the large density of electron-filled Localized States in most photorefractive materials [13] that allow to produce a large density of free electrons in the conduction band (CB), close to the illuminated transparent conduc- tive electrode, by the action of light of adequate wavelength. Free electrons in the CB diffuse to the electrode until a sufficiently large depletion layer and associated electric barrier is build up to stabilize the process. The same barrier but of opposite polarization is build up at the rear photorefractive-electrode interface. As light is strongly absorbed while going through the photorefractive plate thickness, the electric potential barrier is much weaker at the less illuminated rear interface than at the more illuminated front one, as schematically illustrated in Fig. 1. Such an unbalanced voltage difference produces an overall drift of photoelectrons through the ITO-sandwiched photorefractive slab. Photorefractive materials of the Sillenite familly are known to have a large forbidden bandgap (BG) in the range of 3.2 eV (corresponding to a light of k  388 nm) that makes them quite transparent in almost the whole visible range. The action of light on nominally undoped sillenites excites mainly electrons from Localized States in the BG to the CB. The energy gap between the Fermi level and the bottom of the CB in these materials being about 2.2 eV [13–15] (corresponding to k  564 nm), this one should obviously be the minimum photonic energy for photoelectron generation in the sample’s volume, at least in thermally relaxed conditions. Most materials however, and particularly sillenites, have plenty of empty Localized States in between the Fermi level and the CB [15], that may be filled by optical pumping (with light of photonic energy equal to or higher than 2.2 eV, for sillenites) thus allowing light of photonic energy lower (or even much lower) than 2.2 eV to effectively participate in the photoelectric process too. On the other hand, such large number of empty centers makes http://dx.doi.org/10.1016/j.optmat.2016.02.046 0925-3467/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: ivan@ft.unicamp.br (I. de Oliveira). Optical Materials xxx (2016) xxx–xxx Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat Please cite this article in press as: J. Frejlich et al., Opt. Mater. (2016), http://dx.doi.org/10.1016/j.optmat.2016.02.046