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(Si)GeSn nanoelectronics

We investigate the potential of (Si)Ge(Sn) alloys, as well as their tensile strained counterparts, as novel channel materials for future energy efficient nanoelectronic devices, e.g. MOSFETs or tunneling FETs (TFETs). The integration of these alloys requires the development of low temperature processes to suppress device degrading Sn segregations. Therefore, several MOSFET building blocks, e.g. MOS capacitors (MOSCAPs) and contacts, have been investigated.

Figure 1. Sketch of a CV measurement on sGe MOSCAPs [2].Figure 1. : Sketch of a CV measurement on sGe MOSCAPs. Reprinted with permission from ACS Appl. Mater. Interfaces 7, 62-67. Copyright 2015 American Chemical Society [2].

Recently [2] we demonstrated the formation of high-k gate stacks on top of tensile strained Ge(Sn) layers, c.f. Figure 1. For this purpose combinations of HfO2 and Al2O3 were deposited using a low temperature ALD (ALD) process. Temperature- and frequency-dependent capacitance-voltage (CV) measurements were conducted to investigate the electrical properties of these low bandgap materials with special emphasis on the channel/high k interface, exemplarily shown in Figures 2 a)-b).

Figure 2. (a): XTEM image of sGeSn/high-k/metal gate stack. (b):  Temperature dependent CV curves at 1 MHz for sGeSn structure (all from [2]).Figure 2. (a): XTEM image of sGeSn/high-k/metal gate stack. (b): Temperature dependent CV curves at 1 MHz for sGeSn structure. Reprinted with permission from ACS Appl. Mater. Interfaces 7, 62-67. Copyright 2015 American Chemical Society [2].


For contact formation in the metastable (Si)GeSn alloy system, obstacles as the limited thermal budget have to be overcome. In recent studies ([1], [3]) we demonstrated the fabrication of metallic contacts made by Ni alloying of GeSn and SiGeSn. This process is utilized as a standard metallization process in Si nanoelectronics. Figure 3 depict the formation of low-resistive Ni(Si)GeSn phases, which may serve as source/drain stressors in next generation, strain-engineered high-mobility Ge and GeSn MOSFETs.

Figure 3. (a): TEM micrograph of high quality polycrystalline NiGeSn alloy. Figure 3. : TEM micrograph of high quality polycrystalline NiGeSn alloy. © IOP Publishing. Reproduced with permission. All rights reserved [3].

In a recent study [4] we fabricated direct bandgap GeSn p-i-n diodes, the main building blocks for TFETs. The electrical characterization of these devices, which may allow the extraction of material parameters such as tunneling masses, exhibited a distinct region of negative differential resistance with peak-to-valley current ratios up to 2.3 at 4 K, as depicted in Fig. 4 a) and b).

Germanium-Sn PIN diodeFigure 4. : Temperature dependent electrical characterization of p-i-n diode (a), with close up of NDR region (b). Reprinted with permission from Appl. Phys. Let. 107, 042101. Copyright 2015, AIP Publishing LLC [4]. For personal use only. Any other use requires prior permission of the author and the AIP Publishing LLC.

[1] S. Wirths, R. Troitsch, G. Mussler, P. Zaumseil, J.M. Hartmann, T. Schroeder, S. Mantl, and D. Buca,
ECS Transactions, vol. 64, no. 6, pp. 107-112, 2014.
Ni(SiGeSn) Metal Contact Formation on Low Bandgap Strained (Si)Ge(Sn) Semiconductors

[2] S. Wirths, D. Stange, M.-A. Pampillón, A. T. Tiedemann, G. Mussler, A. Fox, U. Breuer, B. Baert, E. San Andrés, N.D. Nguyen, J.M. Hartmann, Z. Ikonic, S. Mantl, and D. Buca,
ACS Appl. Mater. Interfaces, vol. 7, pp. 62–67, 2015.
High-k Gate Stacks on Low Bandgap Tensile Strained Ge and GeSn Alloys for Field-Effect Transistors

[3] 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

[4] C. Schulte-Braucks, D. Stange, N. von den Driesch, S. Blaeser, Z. Ikonic, J.M. Hartmann, S. Mantl, and D. Buca,
Appl. Phys. Let., 107(4), 042101 (2015)
Negative differential resistance in direct bandgap GeSn p-i-n structures


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