Berlin 2018 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 37: Oxide Semiconductors
HL 37.4: Vortrag
Donnerstag, 15. März 2018, 10:15–10:30, EW 203
Excitonic absorption and optical properties of ZnO films — •Stefan Zollner1, Nuwanjula Samarasingha1, Zachary Yoder1, Dipayan Pal2, Aakash Mathur2, Ajaib Singh2, Rinki Singh2, and Sudeshna Chattopadhyay2 — 1New Mexico State University, Las Cruces, NM, USA — 2IIT Indore, Indore, India
Using spectroscopic ellipsometry from 0.5 to 6.5 eV, we have investigated the thickness dependence of the optical constants (complex refractive index, dielectric function) of zinc oxide thin films grown on Si and SiO2 by atomic layer deposition. Independent characterization of the films was carried out using powder x-ray diffraction (texture, grain size), x-ray reflectance (density, thickness, roughness), and atomic force microscopy (roughness). The validity of the ellipsometry results was verified with careful error analysis, including a uniqueness fit for the thickness parameter, and comparison of the thickness with XRR. The dielectric function of ZnO layers was described with an oscillator model guided by measurements for bulk ZnO. Our results show convincingly that both the real and imaginary part of the dielectric function of ZnO on Si decrease with decreasing film thickness. We attribute this thickness dependence to the optical transition matrix element (electron-hole overlap) modified by the interface. The results are not so clear for ZnO on SiO2.