RESEARCH ARTICLE Comparative study of plasmonic resonance in transparent conducting oxides: ITO and AZO Sukla Rajak & Mina Ray Received: 28 June 2013 /Accepted: 10 July 2014 /Published online: 27 July 2014 # The Optical Society of India 2014 Abstract This work aims to report a comparative study of two transparent conducting oxides, namely indium tin oxide (ITO) and aluminium-doped zinc oxide (AZO or ZnO:Al) for the excitation and propagation of surface plasmon polariton wave. Resonance curves for several thicknesses and angle of incidence have been simulated in order to study the resonant behaviour of these materials, using MATLAB. It can be shown that ZnO: Al can support plasmonic excitation by an incident electromagnetic wave of 2.5 micrometer wavelength in MID IR wavelength window. In the frequency range of interest, 200 nm or thicker AZO film gives lower value of minimum reflectivity compared to ITO film for the angle of incidence varying from 42 to 51°, other structural parameters remaining unaltered. Keywords Transparent conducting oxides . Surface plasma waves . Plasmonic resonance . Fano resonance Introduction The collective oscillations of free charges in a material due to an applied electromagnetic field are responsible for plasmonic phenomena occurring at optical and tele- communication frequencies. The essential property of any plasmonic material is that it should have negative real permittivity which would be provided by the free electrons in the material. When an electric field is present within a metal, the free carriers in the metal tend to move in such a manner so as to screen this field. The Drude free carrier model reveals that this screening effect causes negative permittivity. Surface plasma waves (SPWs), a particular mode of guided waves that can be derived from Maxwell ’s equations, propagate along the metal-dielectric interface and sur- face plasmon polaritons (SPPs) are the quantisation of these waves. For coupling between the applied electromagnetic field and SPPs to occur as from Kretschmann configuration (Fig 1), the wave vector on both sides of the conducting layer should be matched and the frequency of the light must be lower than the screened plasma absorption frequency of the conduc- tor. According to Drude free electron model screened plasma frequency ω ps = √ne 2 / με 0 ε ∞ , where n is the charge carrier density, μ is their effective mass, ε 0 is the permittivity of free space and ε ∞ is high fre- quency dielectric constant[1, 2]. For noble metals like gold and silver, ω ps lie in the ultraviolet to visible regions of optical frequencies. This is the main reason behind use of noble metals for most SPW studies in the visible wavelength region. However, due to interband electronic transitions in the metals their uses are limited due to large losses in the visible and ultra-violet (UV) spectral ranges. The metals even with the highest conductivities suffer from large losses at optical frequencies [3, 4] which remained a major obstacle in the design and fabrication of effi- cient plasmonic devices. As alternatives to conventional metals for the produc- tion of transparent electrodes for opto-electronic device applications and solar cells [5–7] transparent conducting S. Rajak Department of Physics, M.U.C. Women’ s College, Burdwan, West Bengal, India e-mail: sukla.phy@gmail.com M. Ray (*) Department of Applied Optics and Photonics, University of Calcutta, JD-2, Sector-III, Salt Lake City, Calcutta, West Bengal, India e-mail: mraphy@caluniv.ac.in J Opt (July–September 2014) 43(3):231–238 DOI 10.1007/s12596-014-0215-8