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In Ultraviolet–Visible (UV–Vis) spectroscopy, the absorption of electromagnetic radiation is used to probe the electronic structure of molecules. This technique provides insights into molecular electronic transitions, particularly the movement of electrons between different molecular orbitals. Radiation is absorbed if the energy of the electromagnetic radiation passing through the molecule is precisely equal to the energy difference between the excited and ground states. During this...
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Using Microwave and Macroscopic Samples of Dielectric Solids to Study the Photonic Properties of Disordered Photonic Bandgap Materials
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Optical Bandgap Definition via a Modified Form of Urbach's Rule.

Mithun Bhowmick1, Haowen Xi2, Bruno Ullrich3

  • 1Department of Mathematical and Physical Sciences, Miami University, Middletown, OH 45042, USA.

Materials (Basel, Switzerland)
|April 3, 2021
PubMed
Summary

This study presents a modified Urbach

Keywords:
GaAsInAsInPInSbUrbach ruleoptical bandgapsemiconductors

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Area of Science:

  • Materials Science
  • Solid State Physics
  • Optoelectronics

Background:

  • Urbach's rule describes the exponential tailing of absorption below the bandgap in semiconductors.
  • The original formulation of Urbach's rule is insufficient for precisely determining the optical bandgap.
  • Accurate optical bandgap determination is crucial for understanding and designing semiconductor devices.

Purpose of the Study:

  • To introduce a novel, esoteric method for determining the optical bandgap of direct gap materials.
  • To demonstrate the utility of a modified Urbach's rule for precise bandgap energy calculation.
  • To derive an explicit expression for the absorption coefficient at the optical bandgap energy.

Main Methods:

  • Modification of Urbach's rule to accurately define the optical bandgap.
  • Application of the modified rule to direct gap semiconductor materials.
  • Derivation of a theoretical expression for the absorption coefficient.

Main Results:

  • The modified Urbach's rule accurately determines the optical bandgap energy.
  • The calculated optical bandgap energy is identical to the threshold energy of band tail absorption.
  • An explicit formula for the absorption coefficient at the optical bandgap energy was obtained.

Conclusions:

  • A modified Urbach's rule provides an accurate method for optical bandgap determination in direct gap materials.
  • This approach bridges the gap between band tail absorption characteristics and precise bandgap energy values.
  • The developed model offers a new tool for optical characterization of semiconductors.