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Title: Optical bandgap of single- and multi-layered amorphous germanium ultra-thin films

Accurate optical methods are required to determine the energy bandgap of amorphous semiconductors and elucidate the role of quantum confinement in nanometer-scale, ultra-thin absorbing layers. Here, we provide a critical comparison between well-established methods that are generally employed to determine the optical bandgap of thin-film amorphous semiconductors, starting from normal-incidence reflectance and transmittance measurements. First, we demonstrate that a more accurate estimate of the optical bandgap can be achieved by using a multiple-reflection interference model. We show that this model generates more reliable results compared to the widely accepted single-pass absorption method. Second, we compare two most representative methods (Tauc and Cody plots) that are extensively used to determine the optical bandgap of thin-film amorphous semiconductors starting from the extracted absorption coefficient. Analysis of the experimental absorption data acquired for ultra-thin amorphous germanium (a-Ge) layers demonstrates that the Cody model is able to provide a less ambiguous energy bandgap value. Finally, we apply our proposed method to experimentally determine the optical bandgap of a-Ge/SiO{sub 2} superlattices with single and multiple a-Ge layers down to 2 nm thickness.
Authors:
;  [1] ;  [2] ;  [3]
  1. Department of Physics and School of Engineering, Brown University, 182-184 Hope St., Providence, Rhode Island 02912 (United States)
  2. Gatan, Inc., 5794 W Las Positas Blvd., Pleasanton, California 94588 (United States)
  3. School of Engineering, Brown University, 184 Hope St., Providence, Rhode Island 02912 (United States)
Publication Date:
OSTI Identifier:
22494858
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 119; Journal Issue: 1; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ABSORPTION; COMPARATIVE EVALUATIONS; CONFINEMENT; GERMANIUM; REFLECTION; SEMICONDUCTOR MATERIALS; SUPERLATTICES; THICKNESS; THIN FILMS