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Correlation of Bandgap Reduction with Inversion Response in (Si)GeSn/High-k/Metal Stacks

Published on 29 March 2018
Correlation of Bandgap Reduction with Inversion Response in (Si)GeSn/High-k/Metal Stacks
Schulte-Braucks C., Narimani K., Glass S., Von Den Driesch N., Hartmann J.M., Ikonic Z., Afanas’ev V.V., Zhao Q.T., Mantl S., Buca D.
Source-TitleACS Applied Materials and Interfaces
Peter Grünberg Institute 9 (PGI 9), JARA-FIT, Forschungszentrum Juelich GmbH, Juelich, Germany, Université Grenoble Alpes, Grenoble, France, CEA, LETI, Minatec Campus, Grenoble, France, Institute of Microwaves and Photonics, Schools of Electronic and Electrical Engineering, University of Leeds, Leeds, United Kingdom, Semiconductor Physics Laboratory, KU Leuven, Leuven, Belgium
The bandgap tunability of (Si)GeSn group IV semiconductors opens a new era in Si-technology. Depending on the Si/Sn contents, direct and indirect bandgaps in the range of 0.4-0.8 eV can be obtained, offering a broad spectrum of both photonic and low power electronic applications. In this work, we systematically studied capacitance-voltage characteristics of high-k/metal gate stacks formed on GeSn and SiGeSn alloys with Sn-contents ranging from 0 to 14 at. % and Si-contents from 0 to 10 at. % particularly focusing on the minority carrier inversion response. A clear correlation between the Sn-induced shrinkage of the bandgap energy and enhanced minority carrier response was confirmed using temperature and frequency dependent capacitance voltage-measurements, in good agreement with k.p theory predictions and photoluminescence measurements of the analyzed epilayers as reported earlier. The enhanced minority generation rate for higher Sn-contents can be firmly linked to the bandgap reduction in the GeSn epilayer without significant influence of substrate/interface effects. It thus offers a unique possibility to analyze intrinsic defects in (Si)GeSn epilayers. The extracted dominant defect level for minority carrier inversion lies approximately 0.4 eV above the valence band edge in the studied Sn-content range (0-12.5 at. %). This finding is of critical importance since it shows that the presence of Sn by itself does not impair the minority carrier lifetime. Therefore, the continuous improvement of (Si)GeSn material quality should yield longer nonradiative recombination times which are required for the fabrication of efficient light detectors and to obtain room temperature lasing action. © 2017 American Chemical Society.
defects, direct band gap, generation/recombination, GeSn, high-k/metal gate
Capacitance, Carrier lifetime, Defects, Epilayers, Germanium alloys, Silicon, Tin, Capacitance voltage characteristic, Direct band gap, Frequency-dependent capacitance, generation/recombination, GeSn, High-k/metal gates, Non-radiative recombinations, Photoluminescence measurements, Energy gap

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