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GeSnSi CVD Epitaxy using Silane, Germane, Digermane, and Tin tetrachloride
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.
(Deaprtment of Physics and Astronomy, Uppsala University)
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
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(English)Article in journal (Refereed) Submitted
Abstract [en]

In this study, strain relaxed and compressive strained Ge1-x-ySnxSiy (0.015≤x≤0.15 and 0≤y≤0.15) layers were epitaxially grown on Si substrate in a chemical vapor deposition reactor at atmospheric pressure. Digermane (Ge2H6) and germane (GeH4) were used as Ge precursors and tin tetrachloride (SnCl4) was used as Sn precursor. The growth temperature was kept below 400ᵒC to suppress Sn out diffusion. The layers crystal quality and strain were characterized using XRD, high resolution reciprocal lattice mapping and transmission electron microscopy and the surface morphology was investigated by atomic force microscopy (AFM). Furthermore, the low temperature epitaxial growth up to 15% Si atoms incorporation in Ge0.94Sn0.06 was demonstrated by adding silane (SiH4) as Si precursor. Sn contents calculated from high resolution XRD patterns were confirmed by Rutherford backscattering spectroscopy which shows that Sn atoms are mostly positioned in substitutional sites. AFM analysis showed below 1nm surface roughness for both strained and strain relaxed GeSn layers which make the promising materials for photonics and electronics applications.

National Category
Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-192065OAI: oai:DiVA.org:kth-192065DiVA: diva2:957850
Note

QC 20160906

Available from: 2016-09-05 Created: 2016-09-05 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.
Series
TRITA-ICT, 2016:20
Keyword
Thermoelectric, SiGe, GeSn(Si), Chemical vapor deposition, Nanowires
National Category
Nano Technology Other Physics Topics
Research subject
Physics
Identifiers
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)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research , EM11-0002
Note

QC 20160907

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

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