**3. Summary and conclusion**

of about 5 × 1020 atoms cm−3, which is located at around 60 nm below the surface of the sample. As a result of the activation annealing, the Se atoms diffused further into the substrate decreasing the maximum Se concentration at a depth of 60 nm from 5 × 10<sup>20</sup> to about 1 × 1020 at cm−3.

integrated and normalized XRD peak data extracted in-situ during the annealing of a sample with Se doping. (c) Integrated

Ge(002) and PdGe(101)

**Figure 23.** (a) In-situ X-ray diffractogram obtained from an Se-doped sample. (b) Pd(111), Pd<sup>2</sup>

and normalized XRD peak data for a sample without Se doping [15].

86 Advanced Material and Device Applications with Germanium

Some of the novel interface control processes developed for the fabrication of NiGe and PdGe Schottky and ohmic contacts on *n*-type germanium have been reviewed.

NiGe grown using the cyclic stacking of Ni/Ge films on an *n*-Ge substrate showed a stable sheet resistivity in the annealing temperature range from 275 to around 500°C. This temperature range was much wider than the corresponding stable-sheet-resistance annealing temperature range obtained from NiGe grown under similar conditions but without the cyclic stacking. The Schottky potential barrier heights for the contacts with cyclically stacked NiGe exhibited stable values which were less than 0.54 eV, even after annealing at temperatures of up to 600°C. The ideality factors of these contacts were less than 1.2, even after annealing at temperatures of up to 500°C. NiGe contacts with the interface incorporation of phosphorus atoms and the insertion of a silicon film at the interface were explained. Ohmic characteristics have been observed for contacts with substantial P interface incorporation and those with minimal P interface incorporation coupled with the insertion of a 0.1 nm-thick Si film, which is essentially a monoatomic Si layer.

A linear relationship was observed between the potential barrier heights and corresponding ideality factors for Schottky contacts of Pd grown on Sb-doped Ge(111) with a doping density of about 2.5 × 1015 cm−3. Current-voltage and capacitance-voltage characteristics were obtained at room temperature. The effective potential barrier heights obtained from these I-V characteristics varied from 0.492 to 0.550 eV, while the ideality factor varied from 1.140 to 1.950. The barrier heights obtained from the reverse bias capacitance-voltage (C−2-V) varied from 0.427 to 0.509 eV. A Gaussian distribution function was fitted over the experimental potential barrier height distributions, resulting in average values of 0.529 and 0.463 eV from I-V and C−2-V characteristics, respectively.

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[5] Patterson JK, Park BJ, Ritley K, Xiao HZ, Allen LH, Rockett A. Kinetics of Ni/a-Ge bilayer

[6] Gaudet S, Detavernier C, Lavoie C, Desjardins P. Reaction of thin Ni films with Ge:

[8] Knaepen W. Characterization of solid state reactions and crystallization in thin films

[9] Hökelek E, Robinson GY. A comparison of Pd Schottky contacts on InP, GaAs and

[10] Comrie CM, Pondo KJ, van der Walt C, Smeets D, Demeulemeester J, Habanyama A, Knaepen W, Detavanier C, Vantomme A. Determination of the dominant diffusing species during nickel and palladium germanide formation. Thin Solid Films. 2012;**526**:261-268

[11] Chilukusha D, Pineda-Vargas CA, Nemutudi R, Habanyama A, Comrie CM. Microprobe PIXE study of Ni-Ge interactions in lateral diffusion couples. Nuclear Instruments and

[12] Motoki M. Interface control process for metal/germanium Schottky contact [MSc thesis].

[13] Chawanda A, Roro KT, Auret FD, Mtangi W, Nyamhere C, Nel J, Leach L. Determination of the laterally homogeneous barrier height of palladium Schottkybarrier diodes on

[14] Güler G, Karatas S, Güllül Ö, Bakkaloglu ÖF. The analysis of lateral distribution of barrier height in identically prepared Co/n-Si Schottky diodes. Journal of Alloys and

[15] Descoins M, Perrin Toinin J, Zhiou S, Hoummada K, Bertoglio M, Ma R, Chow L, Narducci D, Portavoce A. PdGe contact fabrication on Se-doped Ge. Scripta Materialia.

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using in situ X-ray diffraction [PhD thesis]. University of Ghent; 2010

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and NiGe by reaction of Ni film with Ge. Applied Physics Letters. 2006;**89**:131920

Interface Control Processes for Ni/Ge and Pd/Ge Schottky and Ohmic Contact Fabrication: Part Two

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Ni<sup>5</sup> Ge<sup>3</sup>

The sheet resistivity of PdGe grown by Pd reactive diffusion on Ge substrates which had their surfaces implanted with Se atoms was two times lower than that for samples grown under the same conditions but without Se implantation. This result suggests that Se atoms at the Pd/*n*-Ge interface may be used to produce efficient PdGe contacts. The presence of the Se atoms does not modify either the phase-formation sequence or the phase growth kinetics during the Pd reactive diffusion with the Ge substrate, as seen in **Figure 23**.

The three interface control processes analyzed, namely the interface incorporation of P atoms, the thin film insertion of Si at the interface, and the implantation of Se atoms into the surface of the semiconductor substrate, have been demonstrated to be effective, and are therefore recommended for the improvement of Ni and Pd contacts in the next generation of *n*-type germanium-based nanoelectronic devices.
