| AVS 66th International Symposium & Exhibition | |
| Spectroscopic Ellipsometry Focus Topic | Wednesday Sessions |
| Session EL+AS+EM+TF-WeM |
| Session: | Optical Characterization of Thin Films and Nanostructures |
| Presenter: | Flavia Inbanathan, Ohio University |
| Authors: | F.P.N. Inbanathan, Ohio University M. Ebdah, King Saud University, Kingdom of Saudi Arabia P. Kumar, Gurukula Kangri Vishwavidyalaya, India K. Dasari, Texas State University R.S. Katiyar, University of Puerto Rico W.M. Jadwisienczak, Ohio University |
| Correspondent: | Click to Email |
Cadmium Selenide(CdSe), a n-type semiconductor with a direct bandgap of 1.73eV has been explored widely for its suitability in various applications including photovoltaics and optoelectronics, because of its optical and electrical properties. The literature presents various deposition methods for CdSe thin films out of which this work is based on pulsed laser deposition(PLD)[1]. The optoelectronic applications of CdSe thin films depend on their structural and electronic properties that depends on deposition and process parameters[2]. The stability of the thin films at various temperatures is an important factor to improve the efficiency and durability of photosensitive devices. The present work aims to fabricate the high quality CdSe thin films using PLD method and affirms the optimal deposition temperature at 250°C as validated by the films surface roughness and ellipsometry studies[3][4]. The effect of different in-situ deposition temperature on structural, morphological and optical properties through XRD, AFM, SEM, optical absorption/transmission and ellipsometry spectroscopy have been investigated. CdSe thin films with thickness close to 200nm were deposited on the Indium Tin Oxide (ITO) coated glass substrates at temperatures ranging from 150 to 400°C. The light absorption spectrum analysis of all the CdSe films confirmed well defined direct energy band gap from 2.03 to 1.83eV. The ITO substrate is modelled using a two sub-layers model that consists of 130nm graded ITO on top of a 0.7mm bulk ITO layer, and the experimental ellipsometry spectra agreed very well with the fitting spectra. The ellipsometry study confirmed that CdSe thin films show an increase of 44% in refractive index(n) in the violet spectrum, and a constant value in blue-yellow spectral range but with significant changes in red spectrum for increase in temperature upto 350°C; beyond which resulted in constant value, possibly due to the stagnation in the grain growth. The extinction coefficient(k) value of CdSe approaches zero in the red spectrum region for 150oC and 300oC temperatures whereas it showed a value of 0.25 and 0.7 for 250oC and 400oC temperatures, respectively. The peaks observed around 650nm and 750nm in ellipsometry spectra are assigned to excitonic transitions. The collected data will be critically analysed in terms of CdSe optical properties engineered for optoelectronic and photovoltaic applications.
References: [1]Z.Bao et al.,J.Mater.Sci.:Mater Electron(2016)27,7233-7239; [2]S.Mahato, et al., J.Scien.: Adv.Mater. Devices, (2017)2,165-171; [3]A.Evmenova et al.,Advan. Mater. Scien.Eng. (2015), ID 920421,11; [4]B.T.Diroll et al., Chem. Mater.,(2015)27,6463-6469.