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Engineering Multicomponent Nanostructures for MOSFET, Photonic Detector and Hybrid Solar Cell Applications
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.ORCID iD: 0000-0002-4780-1281
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Silicon technologyhas been seekingfor a monolithic solution for a chip where data processing and data communication is performed in the CMOS part and the photonic component, respectively. Traditionally, silicon has been widely considered for electronic applications but not for photonic applications due to its indirect bandgap nature. However, band structure engineering and manipulation through alloying Si with Ge and Sn has opened new possibilities. Theoretical calculations show that it is possible to achieve direct transitions from Ge ifit is alloyed with Sn. Therefore, a GeSn system is a choice to get a direct bandgap. Extending to ternary GeSnSi and quaternary GeSnSiCstructures grown on Si wafers not only makes the bandgap engineering possible but also allowsgrowing lattice matched systems with different strain and bandgaps located in the infrared region. Different heterostructures can be designed and fabricated for detecting lightas photonic sensing oremitting the light as lasers. Alloying not only makes engineering possible but it also induces strain which plays an important role for electronic applications. Theoretical and experimental works show that tensile strain could increase the mobility, which is promising for electronic devices where high mobility channels for high performance MOSFETs is needed to speed up the switching rate. On the other hand, high n-doping in tensile strains in p-i-n structures makesΓ band transitions most probable which is promising for detection and emission of the light. As another benefit of tensile strain, the direct bandgap part shrinks faster than the indirect one if the strain amount is increased.

To get both electronic and photonic applications of GeSn-based structures, two heterostructures (Ge/GeSn(Si)/GeSi/Ge/Si and Ge/GeSn/Si systems), including relaxed and compressive strained layers used to produce tensile strained layers, were designed in this thesis. The low temperature growth is of key importance in this work because the synthesis of GeSn-based hetrostructures on Si wafers requires low thermal conditions due tothe large lattice mismatch which makes them metastable. RPCVD was used to synthesize theseheterostructures because not only it offers a low temperature growth but also because it is compatible with CMOS technology. For utilization of these structures in devices, n-type and p-type doping of relaxed and compressive strained layers were developed. HRRLMs, HRTEM, RBS, SIMS, and FPP techniques were employed to evaluatestrain, quality, Sn content and composition profile of the heterostructures.

The application of GeSn-based heterostructures is not restricted to electronics and photonics. Another application investigated in this work is photovoltaics. In competition with Si-based solar cells, which have, or areexpected to have,high stability and efficiency, thirdgeneration solar cells offer the use of low cost materials and production and can therefore be an alternative for future light energy conversion technology. Particularly, quantum dot sensitized solar cells are associated with favorable properties such as high extrinsic coefficients, size dependent bandgaps and multiple exciton generation and with a theoretical efficiencyof 44%. In this work, two categories of QDs, Cd-free and Cd-based QDs were employed as sensitizers in quantum dot sensitized solar cells (QDSSCs). Cd-based QDs have attracted large interest due to high quantum yield,however, toxicityremains still totheir disadvantage. Mn doping as a bandgap engineering tool for Cd-based type IIZnSe/CdS QDs wasemployed to boostthe solar cell efficiency. Theoretical and experimental investigations show that compared to single coreQDSSCs,typeII core-shells offer higher electron-hole separation due to efficient band alignment where the photogenerated electrons and holes are located in the conduction band of the shell and valence band of the core, respectively. This electron-hole separation suppresses recombination and by carefully designing the band alignment in the deviceit can increase the electron injection and consequently the power conversion efficiency of the device.

Considering eco-friendly and commercialization aspects, three different “green” colloidal nanostructures having special band alignments, which are compatible for sensitized solar cells, were designed and fabricated by the hot injection method. Cu2GeS3-InP QDs not only can harvest light energy up to the infraredregion but can also be usedastypeII QDs. ZnS-coating was employed as a strategy to passivate the surface of InP QDs from interaction with air and electrolyte. In addition, ZnS-coating and hybrid passivation was applied for CuInS2QDs to eliminate surface traps.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , x, 88 p.
Series
TRITA-BIO-Report, ISSN 1654-2312 ; 2015:16
Keyword [en]
Epitaxial G rowth, Reduced Pressure Chemical Vapor Deposition, GeSnSiC, MOSFET, Photonic Detector, Resistivity, Phosp hor and Boron doping, Colloidal QDs Sensitized Solar Cell, Cd - free and Cd - based QDs, High Resolution Reciprocal Lattice Map, High Resolution X - Ray Diffraction, High Resolution Transmission Electron Microscopy, High resolution Scanning E lectron Microscopy .
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-177609ISBN: 978-91-7595-772-2 (print)OAI: oai:DiVA.org:kth-177609DiVA: diva2:873779
Public defence
2015-12-16, FP41, AlbaNova, Roslagstullsbacken 33, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20151125

Available from: 2015-11-25 Created: 2015-11-24 Last updated: 2015-11-25Bibliographically approved
List of papers
1. Growth of GeSnSiC layers for photonic applications
Open this publication in new window or tab >>Growth of GeSnSiC layers for photonic applications
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2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 230, 106-110 p.Article in journal (Refereed) Published
Abstract [en]

This work presents epitaxial growth of intrinsic and doped GeSnSiC layers using Ge2H6, SnCl4, CH3SiH3, B2H6, PH3 and Si2H6 deposited at 290-380 degrees C on strain relaxed Ge buffer layer or Si substrate by using reduced pressure chemical vapor deposition (RPCVD) technique. The GeSnSi layers were compressively strained on Ge buffer layer and strain relaxed on Si substrate. It was demonstrated that the quality of epitaxial layers is dependent on the growth parameters and that the Sn content in epi-layers could be tailored by growth temperature. The Sn segregation caused surface roughness which was decreased by introducing Si and Si-C into Ge layer. The Sn content in GeSn was carefully determined from the mismatch, both parallel and perpendicular, to the growth direction when the Poisson ratio was calculated for a certain Ge-Sn composition. The X-ray results were excellently consistent with Rutherford Backscattered Spectroscopy (RBS). Strain relaxed GeSn layers were also used as virtual substrate to grow tensile-strained Ge layers. The Ge cap layer had low defect density and smooth surface which makes it a viable candidate material for future photonic applications.

Keyword
GeSnSi, Sn segregation, Strain engineering, RPCVD, Germanium
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-129442 (URN)10.1016/j.surfcoat.2013.06.074 (DOI)000323855700017 ()2-s2.0-84881311813 (Scopus ID)
Funder
Swedish Research CouncilEU, European Research Council
Note

QC 20131002

Available from: 2013-10-02 Created: 2013-09-30 Last updated: 2017-12-06Bibliographically approved
2. Growth of GeSnSi Alloys by Reduced Pressure CVD
Open this publication in new window or tab >>Growth of GeSnSi Alloys by Reduced Pressure CVD
(English)Manuscript (preprint) (Other academic)
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-177642 (URN)
Note

QS 2015

Available from: 2015-11-25 Created: 2015-11-25 Last updated: 2015-11-25Bibliographically approved
3. Strain engineering in GeSnSi materials
Open this publication in new window or tab >>Strain engineering in GeSnSi materials
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2012 (English)In: SiGe, Ge, and related compounds 5: materials, processing, and devices, Electrochemical Society, 2012, no 9, 527-531 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this study, Ge1-x-ySnxSiy layers (0.01≤x≤ 0.06 and 0≤y≤0.12) using Ge2H6, SnCl4 (SnD4) and Si2H6 have successfully grown at 290-310 °C on Ge virtual layer on Si(100) by using RPCVD technique. It has been demonstrated that the quality of epitaxial layers is dependent on the growth parameters, layer thickness and the quality of Ge virtual layer. The incorporation of P and B in GeSn matrix has been studied and the effect of dopant specie and concentration on Sn content has been presented. It was found that a proper balance of P, B or Si and Sn flux during the epitaxy improves the incorporation of Sn in Ge matrix. This is explained by the compensation of tensile strain induced by dopants or Si with the compressive strain caused by Sn to obtain the minimum energy in Ge matrix. P-i-n type doped structures of Ge-Sn-Si were grown and the layer quality was analyzed.

Place, publisher, year, edition, pages
Electrochemical Society, 2012
Series
ECS Transactions, ISSN 1938-5862 ; 50
Keyword
Compressive strain, Doped structures, Effect of dopants, Growth parameters, Layer thickness, Minimum energy, Strain engineering, Virtual layers
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-144744 (URN)10.1149/05009.0527ecst (DOI)000338015300062 ()2-s2.0-84881311746 (Scopus ID)978-160768357-5 (ISBN)
Conference
5th SiGe, Ge, and Related Compounds: Materials, Processing and Devices Symposium - 220th ECS Meeting; Honolulu, HI; United States; 7 October 2012 through 12 October 2012
Note

QC 20140512

Available from: 2014-05-12 Created: 2014-04-29 Last updated: 2015-11-25Bibliographically approved
4. Characterization of Ni(Si,Ge) films on epitaxial SiGe(100) formed by microwave annealing
Open this publication in new window or tab >>Characterization of Ni(Si,Ge) films on epitaxial SiGe(100) formed by microwave annealing
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2012 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, no 9, 092101- p.Article in journal (Refereed) Published
Abstract [en]

Microwave annealing (MWA) is investigated as an alternative technique to rapid thermal processing with halogen lamp heating (RTP) for low-temperature silicide formation on epitaxially grown Si0.81Ge0.19 layers. Phase formation, resistivity mapping, morphology analysis, and composition evaluation indicate that the formation of low-resistivity NiSi1-xGex by means of MWA occurs at temperatures about 100 degrees C lower than by RTP. Under similar annealing conditions, more severe strain relaxation and defect generation are therefore found in the remaining Si0.81Ge0.19 layers treated by MWA. Although silicidation by microwave heating is in essence also due to thermal effects, details in heating mechanisms differ from RTP.

Keyword
Strained Silicon, Temperature, Si1-Xgex, Si, Transistors, Technology, Defects, Layers, Nisi2
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-104251 (URN)10.1063/1.4748111 (DOI)000308408100029 ()2-s2.0-84865845972 (Scopus ID)
Note

QC 20121106

Available from: 2012-11-06 Created: 2012-10-31 Last updated: 2017-12-07Bibliographically approved
5. Efficiency Enhanced Colloidal Mn-Doped Type II Core/Shell ZnSe/CdS Quantum Dot Sensitized Hybrid Solar Cells
Open this publication in new window or tab >>Efficiency Enhanced Colloidal Mn-Doped Type II Core/Shell ZnSe/CdS Quantum Dot Sensitized Hybrid Solar Cells
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2015 (English)In: Journal of Nanomaterials, ISSN 1687-4110, E-ISSN 1687-4129, 921903Article in journal (Refereed) Published
Abstract [en]

Colloidal Mn-doped ZnSe/CdS core/shell quantum dots (QDs) are synthesized for the first time and employed as a strategy to boost the power conversion efficiency of quantum dot sensitized solar cells. By using Mn-doping as a band gap engineering tool for core/shell QDs an effective improvement of absorption spectra could be obtained. The mid-states generated by a proper Mn content alleviate carrier separation and enhance the electron injection rate, thus facilitating electron transport to the TiO2 substrate. It is demonstrated that a device constructed with 0.25% Mn-doped ZnSe/CdS leads to an enhancement of the electron injection rate and power conversion efficiency by 4 times and 1.3, respectively.

Place, publisher, year, edition, pages
Hindawi Publishing Corporation, 2015
Keyword
In-Situ Growth, Semiconductor Nanocrystals, Electron-Transport, Optical-Properties, Strained Si, Band, Films, Nanoparticles, Luminescence, Passivation
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-176996 (URN)10.1155/2015/921903 (DOI)000363630700001 ()2-s2.0-84945898089 (Scopus ID)
Note

QC 20151116

Available from: 2015-11-16 Created: 2015-11-13 Last updated: 2017-12-01Bibliographically approved
6. Synthesisof Cd-Free and Low Toxic Cu2GeS3-Inp Quantum Dots For Infrared Solar Cell Applications
Open this publication in new window or tab >>Synthesisof Cd-Free and Low Toxic Cu2GeS3-Inp Quantum Dots For Infrared Solar Cell Applications
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(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-177644 (URN)
Note

QS 2015

Available from: 2015-11-25 Created: 2015-11-25 Last updated: 2015-11-25Bibliographically approved
7. Green” Colloidal InP/ZnS Quantum Dot Sensitized Solar Cells
Open this publication in new window or tab >>Green” Colloidal InP/ZnS Quantum Dot Sensitized Solar Cells
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(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-177646 (URN)
Note

QS 2015

Available from: 2015-11-25 Created: 2015-11-25 Last updated: 2015-11-25Bibliographically approved
8. Strategiesto Improve Photovoltaic Performance of “Green” CuInS2 Quantum Dots: Hybrid Passivation vs Use of ZnS shells
Open this publication in new window or tab >>Strategiesto Improve Photovoltaic Performance of “Green” CuInS2 Quantum Dots: Hybrid Passivation vs Use of ZnS shells
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(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-177647 (URN)
Note

QS 2015

Available from: 2015-11-25 Created: 2015-11-25 Last updated: 2015-11-25Bibliographically approved

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Jamshidi Zavaraki, Asghar

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