Enhancement of persistent photoconductivity of ZnO nanorods under polyvinyl alcohol encapsulation Sayan Bayan a,n , Sheo K. Mishra b , Biswarup Satpati a , Purushottam Chakraborty a a Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064, India b Department of Physics, University of Lucknow, Lucknow 226007, India article info Keywords: Semiconductors Polymer Nanostructures Photoconductivity abstract We report on the observation of enhanced and persistent ultraviolet (UV) photoconduc- tivity of polyvinyl alcohol (PVA) encapsulated ZnO nanorods. A simple aqueous solution growth technique is adopted to grow ZnO nanorods in the form of thin film as well as powder. The morphological features of nanorods (before and after PVA coating) have been studied using electron microscopy. Both bare and PVA coated nanorods are found to exhibit photoconductivity under UV light illumination. PVA encapsulation of nanorods has led to the lower adsorption of oxygen molecules on the surface of nanorods leading to the exhibition of high dark current and a slower growth in photocurrent under steady illumination. The appealing aspect of the present investigation lies in the observation of highly enhanced persistent photoconductivity in the encapsulated nanorods. Based on the fact of confinement of the desorbed oxygen molecules, a new mechanism has been proposed to support the encapsulation led enhancement in persistent photoconductivity. The encapsulation led confinement of the desorbed oxygen molecules around the nanorods results in the faster development of surface built-in potential and hence exhibits enhanced persistent photoconductivity, thereby indicating the uniqueness of the proposed mechanism. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Recently the scientific community has shown consider- able interest in the development of materials applicable for the detection of ultra-violet (UV) light of the electro- magnetic spectrum [1,2]. UV photodetection is essential not only for health and environment related issues but also a vital subject for various optical communication and military applications [1]. Accordingly development of UV detectors based on wide band gap materials is encouraged owing to the several limitations of the existing photode- tectors at their individual level [2]. Amongst various wide band gap materials, zinc oxide (ZnO) (E g  3.37 eV at room temperature) is promising for application in light emitting and detecting devices that work in the ultraviolet (UV) region [3–5]. One-dimensional nanostructures of zinc oxide (ZnO) are considered as potential candidates for their application in UV photodetection [4,5]. Compared to the thin film of ZnO, the nanorods of ZnO are found to exhibit higher photoresponse in terms of photo-to-dark current ratio and responsivity [6]. With the advancement of fabrication and processing technology it has been possible to fabricate a quality photodetector based on one-dimensional nanostructures of ZnO [7,8]. In addition, reports on the enhancement of UV photoconductivity aspects of ZnO nanomaterials upon coating with metal nanoparticles or polymers are also available [9–11]. Poly- mer coating over ZnO nanostructures has been found to be efficient for the enhancement of photoresponse [10,11]. In addition to that, the improvement in photoconductivity Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing http://dx.doi.org/10.1016/j.mssp.2014.03.039 1369-8001/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: sayan.bayan@gmail.com (S. Bayan). Materials Science in Semiconductor Processing 24 (2014) 200–207