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Direct Bandgap Group IV Alloys

Monolithic integration of Si-based photonics and electronics is known to be one key development for energy-efficient computing. Silicon-germanium-tin alloys, such as GeSn, SiGeSn or tensile strained Ge are predestinated group IV semiconductors for this technology since band-engineering allows the fabrication of direct bandgap materials. Not only passive optoelectronic components, but also light emitting devices like lasers and LEDs would strongly benefit from this intrinsic material property. Moreover, a fundamental direct bandgap below 0.5 eV will facilitate novel device concepts for low-power transistors, i.e. Tunnel FETs.

In order to continuously reduce the energy consumption of integrated circuits (ICs), new device structures, new materials and strain engineering have been proposed and investigated. Especially, monolithic integration of Si-based electronics and photonics is known to be key development for energy-efficient computing. Silicon-germanium-tin alloys, such as GeSn, SiGeSn or strained Ge are predestinated group-IV semiconductors for this technology since band-engineering allows the fabrication of direct bandgap materials. A direct bandgap nature Direct bandgap can be achieved in both fully strain-relaxed (Si)GeSn alloys and highly tensile strained Ge or GeSn alloys. This paradigm shift allows the development of efficient optoelectronic components Optoelectronic Applications, i.e. light emitting diodes (LED) and even laser sources [1].

Sketch of a GeSn laser exhibiting a fundamental direct bandgapFigure 1. : Sketch of a GeSn laser exhibiting a fundamental direct bandgap


Moreover, the use of tensile strained Ge(Sn) will boost the performance of p-type transistors in CMOS circuitry, while n-type transistors may benefit from significantly higher electron mobilities from the Γ-valley. High local strain, e.g. applied by (Si)GeSn source/drain stressors as shown in will have substantial impact on future concepts of advanced CMOS as well as ultra-low power devices such as Tunnel-FETs.

S/D stressorsFigure 2. : Sketch of a Ge-MOSFET with SiGeSn source/drain stressors applying local strain within the channel for higher carrier mobilities. © IOP Publishing. Reproduced with permission. All rights reserved [2].


The material development of (Si)GeSn alloys and their application for optoelectronic as well as nanoelectronic devices with the technology available in PGI-9 allows us to take the next step towards energy efficient electronic-photonic ICs (EPICs).

[1] S. Wirths, R. Geiger, N. von den Driesch, G. Mussler, T. Stoica, S. Mantl, Z. Ikonic, M. Luysberg, S. Chiussi, J. M. Hartmann, H. Sigg, J. Faist, D. Buca, and D. Grützmacher,
Nat. Photonics, vol. 9, pp. 88–92, 2015.
Lasing in direct-bandgap GeSn alloy grown on Si

[2] S. Wirths, R. Troitsch, G. Mussler, J.M. Hartmann, P. Zaumseil, T. Schroeder, S. Mantl, D. Buca,
Semicond. Sci. Technol., vol. 30, no. 5, pp. 055003, 2015.
Ternary and quaternary Ni(Si)Ge(Sn) contact formation for highly strained Ge p- and n-MOSFETs


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