Investigation of physical properties of screen printed nanosized ZnO films for optoelectronic applications

¹ Department of Physics, Jamia Millia Islamia, New Delhi 110025, India
² CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012, India

^a e-mail: rayeesphy12@gmail.com

Received: 12 January 2015
Revised: 21 March 2015
Accepted: 25 March 2015
Published online: 24 April 2015

Abstract

Nanosized ZnO particles derived from chemical co-precipitation route were used for casting ZnO films by screen printing method followed by sintering at two different temperatures. The variation in structural, optical and electrical properties of these films with temperature have been investigated by XRD, SEM, FTIR, Raman, UV-VIS, EPR and four probe analytical techniques. XRD patterns of these films exhibit polycrystalline nature with hexagonal wurtzite structure and SEM images reveal the smooth, dense and without any cracks/damage porous surface morphology. Infrared transmission spectra shows peaks pertaining to Zn-O stretching modes and their multiphonon modes. While Raman spectra exhibited strong peaks of E₂ (high) phonon and overtone of surface phonon mode at 429 cm⁻¹ and 1144 cm⁻¹ respectively with weak components of LO and TO branches. The direct band gap energy of these films showed narrowing of band gap from 3.21 eV to 3.12 eV on increasing sintering temperature from 500 °C to 600 °C. DC conductivity measurements confirmed semiconducting behaviour and showed lowering of activation energy. EPR spectra showed single narrow line resonance signal of g-value ~ 1.9469 due to oxygen vacancies which are produced during synthesis of ZnO nanoparticles by sol-gel process. These studies revealed that on increasing sintering temperature the crystallinity of the film improves with reduction in lattice deformations in these screen printed ZnO films.