Effect of Al dopant concentration on structural, optical and photoconducting properties in nanostructured zinc oxide thin films T. Ganesh a,b,n , S. Rajesh a,c , Francis P. Xavier a,d a Loyola Institute of Frontier Energy (LIFE), Loyola College, Chennai 600034, India b PG & Research Department of Physics, Presidency College, Chennai 600005, India c PG & Research Department of Physics, A.M. Jain College, Chennai 600114, India d Loyola-ICAM College of Engineering and Technology, Chennai 600034, India article info Available online 22 November 2012 Keywords: Zinc oxide Sol–gel Spin coating Photoresponse Activation energy abstract Thin films of undoped and doped ZnO, with different Al concentrations (1–5 wt%) were deposited onto glass substrates, by the sol–gel spin coating method. Grazing incidence X- ray diffraction (GIXRD) studies confirmed the nature of films as poly-crystalline, with typical hexagonal wurtzite structure. The films showed variation in crystallite size and change in relative intensities, upon different Al doping concentrations. The surface morphology of the films examined using FE-SEM, showed the grain size becoming smaller upon Al doping. The influence of Al with different concentrations, onto ZnO on the optical absorption and transmittance was studied using UV–Vis–NIR spectrophot- ometer in the wavelength range 300–2500 nm. The UV absorption shifted towards shorter wavelength upon Al doping. The average transmittance in the visible region increased for Al doped films up to 1–2 wt% and decreased for other concentration. The dark and photo conductivity measurements of the films indicated increase in the current values upon doping up to 1–2 wt% of Al and decreased for further concentrations. The rise and decay time measured from the photoresponse study, indicate larger values of rise time for the doped films compared to undoped ZnO. However, the film with 1–2 wt% doping of Al showed better response within the doping concentration. The thermal activation energy obtained from temperature-dependant conductivity showed decrease in the value upon Al doping up to 2 wt% and increased beyond this concentration in the temperature range 300–400 K. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Zinc oxide has got a considerable attention and attrac- tion among the researchers owing to its varied properties and important applications in many areas of opto-elec- tronic devices. It is one of the most important metal oxide semiconductor, existing as n-type with a direct wide bandgap of about 3.3 eV and high exciton binding energy of 60 meV at room temperature. The optical, electrical, thermal and chemical properties of ZnO and its avail- ability in non-toxic form have resulted in its potential application. Thin films of ZnO are used as transparent conductors [1], heat mirrors [2], UV light emitters [3], photocatalyst [4], UV LEDs [5] and photovoltaic devices [6]. Several methods are used to grow ZnO films such as CVD [7], electrodeposition [8], pulsed laser deposition [9], molecular beam epitaxy(MBE) [10] and sol–gel process [11,12]. Among the above methods, sol–gel process is simple, inexpensive, flexible and deposition controlled method to obtain nanostructure ZnO films. Due to high cost and scarcity of indium, ITO substrates can be Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/mssp Materials Science in Semiconductor Processing 1369-8001/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mssp.2012.10.008 n Corresponding author at: PG & Research Department of Physics, Presidency College, Chennai 600005, India. Tel.: þ91 9840640924. E-mail address: ntganesh@yahoo.co.in (T. Ganesh). Materials Science in Semiconductor Processing 16 (2013) 295–302