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Publications (10 of 121) Show all publications
Prusakova, L., Hubik, P., Aijaz, A., Nyberg, T. & Kubart, T. (2020). Room Temperature Reactive Deposition of InGaZnO and ZnSnO Amorphous Oxide Semiconductors for Flexible Electronics. Coatings, 10(1), Article ID 2.
Open this publication in new window or tab >>Room Temperature Reactive Deposition of InGaZnO and ZnSnO Amorphous Oxide Semiconductors for Flexible Electronics
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2020 (English)In: Coatings, ISSN 2079-6412, Vol. 10, no 1, article id 2Article in journal (Refereed) Published
Abstract [en]

Amorphous oxide semiconductors (AOSs) are interesting materials which combine optical transparency with high electron mobility. AOSs can be prepared at low temperatures by high throughput deposition techniques such as magnetron sputtering and are thus suitable for flexible transparent electronics such as flexible displays, thin-film transistors, and sensors. In magnetron sputtering the energy input into the growing film can be controlled by the plasma conditions instead of the substrate temperature. Here, we report on magnetron sputtering of InGaZnO (IGZO) and ZnSnO (ZTO) with a focus on the effect of deposition conditions on the film properties. IGZO films were deposited by radio-frequency (RF) sputtering from an oxide target while for ZTO, reactive sputtering from an alloy target was used. All films were deposited without substrate heating and characterized with respect to microstructure, electron mobility, and resistivity. The best as-deposited IGZO films exhibited a resistivity of about 2 x 10(-2) Ohm center dot cm and an electron mobility of 18 cm(2)center dot V-1 center dot s(-1). The lateral distribution of the electrical properties in such films is mainly related to the activity and amount of oxygen reaching the substrate surface as well as its spatial distribution. The lateral uniformity is strongly influenced by the composition and energy of the material flux towards the substrate.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
amorphous oxide semiconductors, magnetron sputtering, InGaZnO, ZnSnO
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-407292 (URN)10.3390/coatings10010002 (DOI)000513694500027 ()
Available from: 2020-03-23 Created: 2020-03-23 Last updated: 2020-03-23Bibliographically approved
Englund, S., Kubart, T., Keller, J., Moro, M. V., Primetzhofer, D., Suvanam, S. S., . . . Platzer Björkman, C. (2019). Antimony-Doped Tin Oxide as Transparent Back Contact in Cu2ZnSnS4 Thin-Film Solar Cells. Physica Status Solidi (a) applications and materials science, 216(22), Article ID 1900542.
Open this publication in new window or tab >>Antimony-Doped Tin Oxide as Transparent Back Contact in Cu2ZnSnS4 Thin-Film Solar Cells
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2019 (English)In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 216, no 22, article id 1900542Article in journal (Refereed) Published
Abstract [en]

Antimony-doped tin oxide (Sn2O3:Sb, ATO) is investigated as a transparent back contact for Cu2ZnSnS4 (CZTS) thin-film solar cells. The stability of the ATO under different anneal conditions and the effect from ATO on CZTS absorber growth are studied. It is found that ATO directly exposed to sulfurizing anneal atmosphere reacts with S, but when covered by CZTS, it does not deteriorate when annealed at T < 550 degrees C. The electrical properties of ATO are even found to improve when CZTS is annealed at T = 534 degrees C. At T = 580 degrees C, it is found that ATO reacts with S and degrades. Analysis shows repeatedly that ATO affects the absorber growth as large amounts of Sn-S secondary compounds are found on the absorber surfaces. Time-resolved anneal series show that these compounds form early during anneal and evaporate with time to leave pinholes behind. Device performance can be improved by addition of Na prior to annealing. The best CZTS device on ATO back contact herein has an efficiency of 2.6%. As compared with a reference on a Mo back contact, a similar open-circuit voltage and short-circuit current density are achieved, but a lower fill factor is measured.

Keywords
antimony-doped tin oxides, Cu2ZnSnS4, sulfurization, thin-film solar cells, transparent back contacts
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-402260 (URN)10.1002/pssa.201900542 (DOI)000488074100001 ()
Funder
Swedish Foundation for Strategic Research , FFL13-0178Swedish Foundation for Strategic Research , RMA15‐0030Swedish Foundation for Strategic Research , RIF13‐0053Swedish Research Council, 821‐2012‐5144Swedish Research Council, 2017‐00646 9
Available from: 2020-01-13 Created: 2020-01-13 Last updated: 2020-01-31Bibliographically approved
Tian, L., Törndahl, T., Ling, J., Pati, P. B., Zhang, Z.-B., Kubart, T., . . . Tian, H. (2019). Mechanistic Insights into Solid-State p-Type Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 123(43), 26151-26160
Open this publication in new window or tab >>Mechanistic Insights into Solid-State p-Type Dye-Sensitized Solar Cells
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2019 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 43, p. 26151-26160Article in journal (Refereed) Published
Abstract [en]

The study of p-type dye sensitized solar cells (p-DSCs) is appealing but challenging. Although the devices have been studied for 20 years, the light conversion efficiency lags far behind those of n-DSCs. Very recently, on the basis of a core-shell structure, a novel solid-state p-DSC (p-ssDSCs) has been fabricated, which showed great enhancement in open-circuit voltage and dye regeneration rate. To further improve the performance of such devices, charge diffusion, recombination process, and the main limiting factors have to be understood. In the present paper, core-shell p-ssDSCs with ZnO as an electron conductor were fabricated by atomic layer deposition. The charge transport time was determined to be ca. 0.1 ms, which is about 2 orders of magnitude faster than those of typical liquid devices with I-/I-3(-) as a redox mediator. As a consequence, the devices exhibit the highest reported charge diffusion coefficient (D-d)' among p-DSCs. It is ascribed to an electron-limiting diffusion process by the ambipolar diffusion model, suggesting a different charge-transport-determining mechanism in contrast to liquid p-DSCs. The charge recombination rate is 1-2 orders of magnitude slower than its charge transport time, mandating that the estimated charge collection efficiency is near unity. Detailed analysis of the incident photon-to-electron conversion efficiency suggests that the energy conversion efficiency in these p-ssDSCs is currently limited by a large fraction of dyes that is not fully electrically connected in the device.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Physical Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-397591 (URN)10.1021/acs.jpcc.9b08251 (DOI)000493865700013 ()
Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2020-01-15Bibliographically approved
Jablonka, L., Moskovkin, P., Zhang, Z., Zhang, S.-L., Lucas, S. & Kubart, T. (2019). Metal Filling by High Power Impulse Magnetron Sputtering. Journal of Physics D: Applied Physics, 52(36), Article ID 365202.
Open this publication in new window or tab >>Metal Filling by High Power Impulse Magnetron Sputtering
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2019 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 52, no 36, article id 365202Article in journal (Refereed) Published
Abstract [en]

High power impulse magnetron sputtering (HiPIMS) is an emerging thin film deposition technology that provides a highly ionized flux of sputtered species. This makes HiPIMS attractive for metal filling of nanosized holes for highly scaled semiconductor devices. In this work, HiPIMS filling with Cu and Co is investigated. We show that the quality of the hole filling is determined mainly by the fraction of ions in the deposited flux and their energy. The discharge waveforms alone are insufficient to determine the ionization of the metal flux. The experimental results are in a good agreement with Monte-Carlo simulations using the measured flux characteristics. Based on the simulations, strategies to improve the filling are discussed.

Keywords
metallization, HiPIMS, ionized sputtering
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-384881 (URN)10.1088/1361-6463/ab28e2 (DOI)000474655700001 ()
Funder
Swedish Foundation for Strategic Research , SE13-0033
Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-09-17Bibliographically approved
Keller, J., Chen, W.-C., Riekehr, L., Kubart, T., Törndahl, T. & Edoff, M. (2018). Bifacial Cu(In,Ga)Se2 solar cells using hydrogen‐doped In2O3 films as a transparent back contact. Progress in Photovoltaics, 26(10), 846-858
Open this publication in new window or tab >>Bifacial Cu(In,Ga)Se2 solar cells using hydrogen‐doped In2O3 films as a transparent back contact
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 10, p. 846-858Article in journal (Refereed) Published
Abstract [en]

Hydrogen‐doped In2O3 (IOH) films are used as a transparent back contact in bifacial Cu(In,Ga)Se2 (CIGS) solar cells. The effect of the IOH thickness and the impact of the sodium incorporation technique on the photovoltaic parameters are studied, and clear correlations are observed. It is shown that a loss in short circuit current density (JSC) is the major limitation at back side illumination. The introduction of a thin Al2O3 layer on top of the IOH significantly increases the collection efficiency (ϕ(x)) for electrons generated close to the back contact. In this way, the JSC loss can be mitigated to only ~ 25% as compared with front side illumination. The Al2O3 film potentially reduces the interface defect density or, alternatively, creates a field effect passivation. In addition, it prevents the excessive formation of Ga2O3 at the CIGS/IOH interface, which is found otherwise when a NaF layer is added before absorber deposition. Consequently, detrimental redistributions in Ga and In close to the back contact can be avoided. Finally, a bifacial CIGS solar cell with an efficiency (η) of η = 11.0% at front and η = 6.0% at back side illumination could be processed. The large potential for further improvements is discussed.

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-363288 (URN)10.1002/pip.3025 (DOI)000443696500008 ()
Funder
Swedish Energy Agency, 2016-008376Swedish Foundation for Strategic Research , RMA15-0030
Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2018-11-02Bibliographically approved
Vitelaru, C., Aijaz, A., Parau, A. C., Kiss, A. E., Sobetkii, A. & Kubart, T. (2018). Discharge runaway in high power impulse magnetron sputtering of carbon: the effect of gas pressure, composition and target peak voltage. Journal of Physics D: Applied Physics, 51(16), Article ID 165201.
Open this publication in new window or tab >>Discharge runaway in high power impulse magnetron sputtering of carbon: the effect of gas pressure, composition and target peak voltage
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2018 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 16, article id 165201Article in journal (Refereed) Published
Abstract [en]

Pressure and target voltage driven discharge runaway from low to high discharge current density regimes in high power impulse magnetron sputtering of carbon is investigated. The main purpose is to provide a meaningful insight of the discharge dynamics, with the ultimate goal to establish a correlation between discharge properties and process parameters to control the film growth. This is achieved by examining a wide range of pressures (2-20 mTorr) and target voltages (700-850 V) and measuring ion saturation current density at the substrate position. We show that the minimum plasma impedance is an important parameter identifying the discharge transition as well as establishing a stable operating condition. Using the formalism of generalized recycling model, we introduce a new parameter, 'recycling ratio', to quantify the process gas recycling for specific process conditions. The model takes into account the ion flux to the target, the amount of gas available, and the amount of gas required for sustaining the discharge. We show that this parameter describes the relation between the gas recycling and the discharge current density. As a test case, we discuss the pressure and voltage driven transitions by changing the gas composition when adding Ne into the discharge. We propose that standard Ar HiPIMS discharges operated with significant gas recycling do not require Ne to increase the carbon ionization.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2018
Keywords
magnetron sputtering, carbon sputtering, gas recycling, high power impulse magnetron sputtering (HiPIMS), diamond like carbon (DLC)
National Category
Fusion, Plasma and Space Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-353101 (URN)10.1088/1361-6463/aab590 (DOI)000428686500001 ()
Funder
VINNOVA
Available from: 2018-06-11 Created: 2018-06-11 Last updated: 2018-06-14Bibliographically approved
Keller, J., Chalvet, F., Joel, J., Aijaz, A., Kubart, T., Riekehr, L., . . . Törndahl, T. (2018). Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells. Progress in Photovoltaics, 26(1), 13-23
Open this publication in new window or tab >>Effect of KF absorber treatment on the functionality of different transparent conductive oxide layers in CIGSe solar cells
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2018 (English)In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 26, no 1, p. 13-23Article in journal (Refereed) Published
Abstract [en]

This contribution studies the impact of the KF-induced Cu(In,Ga)Se2 (CIGSe) absorber modification on the suitability of different transparent conductive oxide (TCO) layers in solar cells. The TCO material was varied between ZnO:Al (AZO), ZnO:B (BZO), and In2O3:H (IOH). It is shown that the thermal stress needed for optimized TCO properties can establish a transport barrier for charge carriers, which results in severe losses in fill factor (FF) for temperatures >150°C. The FF losses are accompanied by a reduction in open circuit voltage (Voc) that might originate from a decreased apparent doping density (Nd,app) after annealing. Thermally activated redistributions of K and Na in the vicinity of the CdS/(Cu,K)-In-Se interface are suggested to be the reason for the observed degradation in solar cell performance. The highest efficiency was measured for a solar cell where the absorber surface modification was removed and a BZO TCO layer was deposited at a temperature of 165°C. The presented results highlight the importance of well-designed TCO and buffer layer processes for CIGSe solar cells when a KF post deposition treatment (KF-PDT) was applied.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-332827 (URN)10.1002/pip.2925 (DOI)000418097200002 ()
Funder
Swedish Energy Agency, 2012-004591
Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2018-01-17Bibliographically approved
Ferreira, F., Aijaz, A., Kubart, T., Cavaleiro, A. & Oliveira, J. (2018). Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering. Paper presented at 60th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), APR 29-MAY 04, 2017, Providence, RI. Surface & Coatings Technology, 336, 92-98
Open this publication in new window or tab >>Hard and dense diamond like carbon coatings deposited by deep oscillations magnetron sputtering
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2018 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 336, p. 92-98Article in journal (Refereed) Published
Abstract [en]

Recent developments in the automotive industry to improve engine efficiency and minimize pollutant emissions are driving the need for higher operating temperatures and loading densities in internal combustion engines. Future engines for internal combustion engines will require coatings with increased temperature stability (up to 500 degrees C) and wear resistance as compared to present day solutions. Hard tetrahedral DLC coatings (ta-C coatings) very low coefficient of friction and performed very well under mixed and boundary lubrication, and, thus, they are very attractive for automotive industry. In this work, DLC coatings were deposited by deep oscillations magnetron sputtering (DOMS), a variant of high power magnetron sputtering (HiPIMS). The main objective is to increase the sp(3) content in the films, as compared to d.c. magnetron sputtering (DCMS), and thus extend their operating range to higher temperatures. Increasing the bias voltage results in denser and smoother films with increasing hardness, as measured by nano-indentation, and increasing mass density, as measured by x-ray reflectivity. Accordingly, the UV Raman spectroscopy analysis of the films shows that the sp(3)/sp(2) ratio in the films increases with increasing substrate biasing. However, the sp(3) bonds convert back to sp(2) upon annealing. Never the less, a significantly higher amount of sp(3) bonds is formed in the DLC films deposited by DOMS, as compared to the DCMS ones, showing that DOMS is a promising path for the development of hard DLC films.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
DLC, DOMS, Mass density, Hardness, Temperature stability
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-348847 (URN)10.1016/j.surfcoat.2017.10.055 (DOI)000425478000015 ()
Conference
60th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), APR 29-MAY 04, 2017, Providence, RI
Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2018-05-02Bibliographically approved
Jablonka, L., Riekehr, L., Zhang, Z., Zhang, S.-L. & Kubart, T. (2018). Highly conductive ultrathin Co films by high-power impulse magnetron sputtering. Applied Physics Letters, 112(4), Article ID 043103.
Open this publication in new window or tab >>Highly conductive ultrathin Co films by high-power impulse magnetron sputtering
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2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 4, article id 043103Article in journal (Refereed) Published
Abstract [en]

Ultrathin Co films deposited on SiO2 with conductivities exceeding that of Cu are demonstrated. Ionized deposition implemented by high-power impulse magnetron sputtering (HiPIMS) is shown to result in smooth films with large grains and low resistivities, namely, 14 mu Omega cm at a thickness of 40 nm, which is close to the bulk value of Co. Even at a thickness of only 6 nm, a resistivity of 35 mu Omega cm is obtained. The improved film quality is attributed to a higher nucleation density in the Co-ion dominated plasma in HiPIMS. In particular, the pulsed nature of the Co flux as well as shallow ion implantation of Co into SiO2 can increase the nucleation density. Adatom diffusion is further enhanced in the ionized process, resulting in a dense microstructure. These results are in contrast to Co deposited by conventional direct current magnetron sputtering where the conductivity is reduced due to smaller grains, voids, rougher interfaces, and Ar incorporation. The resistivity of the HiPIMS films is shown to be in accordance with models by Mayadas-Shatzkes and Sondheimer which consider grain-boundary and surface-scattering.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2018
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-340315 (URN)10.1063/1.5011109 (DOI)000423724300039 ()
Funder
Swedish Foundation for Strategic Research , SE13-0033Swedish Foundation for Strategic Research , RIF14-0053Swedish Research Council, C0514401
Available from: 2018-01-29 Created: 2018-01-29 Last updated: 2019-06-13Bibliographically approved
Jablonka, L., Kubart, T., Gustavsson, F., Descoins, M., Mangelinck, D., Zhang, S.-L. & Zhang, Z. (2018). Improving the morphological stability of nickel germanide by tantalum and tungsten additions. Applied Physics Letters, 112(10), Article ID 103102.
Open this publication in new window or tab >>Improving the morphological stability of nickel germanide by tantalum and tungsten additions
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2018 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 10, article id 103102Article in journal (Refereed) Published
Abstract [en]

To enhance the morphological stability of NiGe, a material of interest as a source drain-contact in Ge-based field effect transistors, Ta or W, is added as either an interlayer or a capping layer. The efficacy of this Ta or W addition is evaluated with pure NiGe as a reference. While interlayers increase the NiGe formation temperature, capping layers do not retard the NiGe formation. Regardless of the initial position of Ta or W, the morphological stability of NiGe against agglomeration can be improved by up to 100 °C. The improved thermal stability can be ascribed to an inhibited surface diffusion, owing to Ta or W being located on top of NiGe after annealing, as confirmed by means of transmission electron microscopy, Rutherford backscattering spectrometry, and atom probe tomography. The latter also shows a 0.3 €‰at. % solubility of Ta in NiGe at 450 °C, while no such incorporation of W is detectable.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-344676 (URN)10.1063/1.5019440 (DOI)000427031300021 ()
Funder
Swedish Foundation for Strategic Research , SE13- 0033Swedish Foundation for Strategic Research , RIF14- 0053Swedish Research Council, C0514401
Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2019-06-28Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2679-2387

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