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Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon
Published on: July 17, 2020
Direct bandgap narrowing in Ge LED's on Si substrates
Michael Oehme1, Martin Gollhofer, Daniel Widmann
1Institute for Semiconductor Engineering, University of Stuttgart, 70569 Stuttgart, Germany. oehme@iht.uni-stuttgart.de
Abstract:
In this paper we investigate the influence of n-type doping in Ge light emitting diodes on Si substrates on the room temperature emission spectrum. The layer structures are grown with a special low temperature molecular beam epitaxy process resulting in a slight tensile strain of 0.13%. The Ge LED's show a dominant direct bandgap emission with shrinking bandgap at the Γ point in dependence of n-type doping level. The emission shift (38 meV at 10²⁰cm⁻³) is mainly assigned to bandgap narrowing at high doping. The electroluminescence intensity increases with doping concentrations up to 3x10¹⁹cm⁻³ and decreases sharply at higher doping levels. The integrated direct gap emission intensity increases superlinear with electrical current density. Power exponents vary from about 2 at low doping densities up to 3.6 at 10²⁰cm⁻³ doping density.
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