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Effect of strain on Ni-(GeSn)x contact formation to GeSn nanowires
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits. Nocilis Materials, Sweden .
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.ORCID iD: 0000-0001-5678-5298
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2014 (English)In: Materials Research Society Symposium Proceedings, 2014, Vol. 1707Conference paper (Refereed)
Abstract [en]

In this study, the formation of Ni-(GeSn)x on strained and relaxed Ge1-xSnx (0.01≤x≤ 0.03) nanowires in contact areas has been investigated. The epi-layers were grown at different temperatures (290 to 380°C) by RPCVD technique. The strain in GeSn layers tailored through carefully chosen of growth parameters and virtual substrate. The nanowires were fabricated through both I-line and dry-etching. 15 nm Ni was deposited either on the contact areas or whole length of nanowires. The wires went through rapid thermal annealing at intervals of 360 to 550°C for 30s in N2 ambient. The results show the thermal stability and amount of particular phases were strain-dependent. The formation of Ni-GeSn was eased when GeSn layers were strain-free. When the Sn content is high the epi-layers suffer from Sn segregation. The Sn-rich surface impedes remarkably the Ni diffusion. The electrical conductivity measurement of nanowires shows low resistivity and Ohmic contact are obtained for Ni-GeSn.

Place, publisher, year, edition, pages
2014. Vol. 1707
, Materials Research Society Symposium Proceedings, ISSN 0272-9172
Keyword [en]
Ge, Ni, Sn, Germanium, Nanowires, Ohmic contacts, Rapid thermal annealing, Tin, Contact formation, Effect of strain, Electrical conductivity measurements, Growth parameters, Low resistivity, Strain-dependent, Virtual substrates, Whole lengths, Nickel
National Category
Materials Engineering
URN: urn:nbn:se:kth:diva-167536DOI: 10.1557/opl.2014.559ScopusID: 2-s2.0-84926314889OAI: diva2:819275
2014 MRS Spring Meeting, 21 April 2014 through 25 April 2014

QC 20150610

Available from: 2015-06-10 Created: 2015-05-22 Last updated: 2016-09-06Bibliographically approved
In thesis
1. Growth, processing and characterization of group IV materials for thermoelectric applications
Open this publication in new window or tab >>Growth, processing and characterization of group IV materials for thermoelectric applications
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Discover of new energy sources and solutions are one of the important global issues nowadays, which has a big impact on economy as well as environment. One of the methods to help to mitigate this issue is to recover wasted heat, which is produced in large quantities by the industry, through vehicle exhausts and in many other situations where we consume energy. One way to do this would be using thermoelectric (TE) materials, which enable direct interconversion between heat and electrical energy. This thesis investigates how the novel material combinations and nanotechnology could be used for fabricating more efficient TE materials and devices.

The work presents synthesis, processing, and electrical characterization of group IV materials for TE applications. The starting point is epitaxial growth of alloys of group IV elements, silicon (Si), germanium (Ge) and tin (Sn), with a focus on SiGe and GeSn(Si) alloys. The material development is performed using chemical vapor deposition (CVD) technique. Strained and strain-relaxed Ge1-x Snx (0.01≤x≤0.15) has been successfully grown on Ge buffer and Si substrate, respectively. It is demonstrated that a precise control of temperature, growth rate, Sn flow and buffer layer quality is necessary to overcome Sn segregation and achieve a high quality GeSn layer. The incorporation of Si and n- and p-type dopant atoms is also investigated and it was found that the strain can be compensated in the presence of Si and dopant atoms. 

Si1-xGexlayers are grown on Si-on-insulator wafers and condensed by oxidation at 1050 ᵒC to manufacture SiGe-on-insulator (SGOI) wafers. Nanowires (NWs) are processed, either by sidewall transfer lithography (STL), or by using conventional lithography, and subsequently manufactured into nanoscale dimensions by focused ion beam (FIB) technique. The NWs are formed in an array, where one side is heated by a resistive heater made of Ti/Pt. The power factor of NWs is measured and the results are compared for NWs manufactured by different methods. It is found that the electrical properties of NWs fabricated with FIB technique can be influenced due to Ga doping during ion milling.

Finally, the carrier transport in SiGe NWs formed on SGOI samples is tailored by applying a back-gate voltage on the Si substrate. In this way, the power factor is improved by a factor of 4. This improvement is related to the presence of defects and/or small fluctuation of nanowire shape and Ge content along the NWs, generated during processing and condensation of SiGe layers. The SiGe results open a new window for operation of SiGe NWs-based TE devices in the new temperature range of 250 to 450 K.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 53 p.
TRITA-ICT, 2016:20
Thermoelectric, SiGe, GeSn(Si), Chemical vapor deposition, Nanowires
National Category
Nano Technology Other Physics Topics
Research subject
urn:nbn:se:kth:diva-192142 (URN)978-91-7729-076-6 (ISBN)
External cooperation:
Public defence
2016-09-30, Sal B, Kistagången 16, Kista, 10:00 (English)
Swedish Foundation for Strategic Research , EM11-0002

QC 20160907

Available from: 2016-09-07 Created: 2016-09-06 Last updated: 2016-09-09Bibliographically approved

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