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41 results on '"Yli-Koski, Marko"'

6. Plasma-enhanced atomic layer deposited SiO2 enables positive thin film charge and surface recombination velocity of 1.3 cm/s on germanium.

Author

Liu, Hanchen, Pasanen, Toni P., Leiviskä, Oskari, Isometsä, Joonas, Fung, Tsun Hang, Yli-Koski, Marko, Miettinen, Mikko, Laukkanen, Pekka, Vähänissi, Ville, and Savin, Hele

Subjects
SURFACE recombination, THIN films, SURFACE charges, SURFACE passivation, GERMANIUM, ALUMINUM oxide films
Abstract

The excellent field-effect passivation provided by aluminum oxide (Al2O3) on germanium surfaces relies on the high negative fixed charge present in the film. However, in many applications, a neutral or a positive charge would be preferred. Here, we investigate the surface passivation performance and the charge polarity of plasma-enhanced atomic layer deposited (PEALD) silicon oxide (SiO2) on Ge. The results show that even a 3 nm thick PEALD SiO2 provides a positive charge density (Qtot, ∼2.6 × 1011 cm−2) and a relatively good surface passivation (maximum surface recombination velocity SRVmax ∼16 cm/s). When the SiO2 thin film is capped with an ALD Al2O3 layer, the surface passivation improves further and a low midgap interface defect density (Dit) of ∼1 × 1011 eV−1 cm−2 is achieved. By varying the SiO2 thickness under the Al2O3 capping, it is possible to control the Qtot from virtually neutral (∼2.8 × 1010 cm−2) to moderately positive (∼8.5 × 1011 cm−2) values. Consequently, an excellent SRVmax as low as 1.3 cm/s is obtained using optimized SiO2/Al2O3 layer thicknesses. Finally, the origin of the positive charge as well as the interface defects related to PEALD SiO2 are discussed. [ABSTRACT FROM AUTHOR]

Published
2023
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17. Achieving surface recombination velocity below 10 cm/s in n-type germanium using ALD Al2O3.

Author

Isometsä, Joonas, Fung, Tsun Hang, Pasanen, Toni P., Liu, Hanchen, Yli-koski, Marko, Vähänissi, Ville, and Savin, Hele

Subjects
SURFACE recombination, SURFACE passivation, ALUMINUM oxide films, ALUMINUM oxide, FIELD-effect transistors, GERMANIUM
Abstract

Desirable intrinsic properties, namely, narrow bandgap and high carrier mobility, make germanium (Ge) an excellent candidate for various applications, such as radiation detectors, multi-junction solar cells, and field effect transistors. Nevertheless, efficient surface passivation of Ge has been an everlasting challenge. In this work, we tackle this problem by applying thermal atomic layer deposited (ALD) aluminum oxide (Al2O3), with special focus on the process steps carried out prior to and after dielectric film deposition. Our results show that instead of conventional hydrofluoric acid (HF) dip, hydrochloric acid (HCI) pre-treatment is an essential process step needed to reach surface recombination velocities (SRVs) below 10 cm/s. The main reason for efficient surface passivation is found to be a high dielectric charge that promotes the so-called field-effect passivation. Furthermore, the results demonstrate that the post-deposition anneal temperature, time, and ambient play a role in passivating Ge-dangling bonds, but surprisingly, good surface passivation (SRV below 26 cm/s) is obtained even without any post-deposition annealing. The results pave the way for high-performance n-type Ge optoelectronic devices that could use induced junctions via negatively charged Al2O3 layers. [ABSTRACT FROM AUTHOR]

Published
2021
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24. Light-induced degradation in copper-contaminated gallium-doped silicon

Author

Lindroos, Jeanette, Yli-Koski, Marko, Haarahiltunen, Antti, Schubert, Martin C., Savin, Hele, Publica, Sähkötekniikan korkeakoulu, School of Electrical Engineering, Mikro- ja nanotekniikan laitos, Department of Micro and Nanosciences, Aalto-yliopisto, and Aalto University

Subjects
inorganic chemicals, lifetime, gallium, Silicon, Energy, Physics, technology, industry, and agriculture, silicon, Gallium, complex mixtures, Silicium-Photovoltaik, Degradation, copper, Charakterisierung, Zellen und Module, Charakterisierung von Prozess- und Silicium-Materialien, Copper, degradation, Solarzellen - Entwicklung und Charakterisierung
Abstract

To date, gallium-doped Czochralski (Cz) silicon has constituted a solar cell bulk material free of light-induced degradation. However, we measure light-induced degradation in gallium-doped Cz silicon in the presence of copper impurities. The measured degradation depends on the copper concentration and the material resistivity. Gallium-doped Cz silicon is found to be less sensitive to copper impurities than borondoped Cz silicon, emphasizing the role of boron in the formation of copper-related light-induced degradation.

Published
2013

25. Impact of phosphorus gettering parameters and initial iron level on silicon solar cell properties

Author

Vähänissi, Ville, Haarahiltunen, Antti, Talvitie, Heli, Yli-Koski, Marko, Savin, Hele, Sähkötekniikan korkeakoulu, School of Electrical Engineering, Mikro- ja nanotekniikan laitos, Department of Micro and Nanosciences, Aalto-yliopisto, and Aalto University

Subjects
monocrystalline silicon, iron, silicon solar cells, Physics, phosphorus diffusion gettering
Abstract

We have studied experimentally the effect of different initial iron contamination levels on the electrical device properties of p-type Czochralski-silicon solar cells. By systematically varying phosphorus diffusion gettering (PDG) parameters, we demonstrate a strong correlation between the open-circuit voltage (Voc) and the gettering efficiency. Similar correlation is also obtained for the short-circuit current (Jsc), but phosphorus dependency somewhat complicates the interpretation: the higher the phosphorus content not only the better the gettering efficiency but also the stronger the emitter recombination. With initial bulk iron concentration as high as 2 × 1014 cm−3, conversion efficiencies comparable with non-contaminated cells were obtained, which demonstrates the enormous potential of PDG. The results also clearly reveal the importance of well-designed PDG: to achieve best results, the gettering parameters used for high purity silicon should be chosen differently as compared with for a material with high impurity content. Finally we discuss the possibility of achieving efficient gettering without deteriorating the emitter performance by combining a selective emitter with a PDG treatment.

Published
2012

36. Micro-photoluminescence spectroscopy on metal precipitates in silicon

Author

Gundel, Paul, primary, Schubert, Martin C., additional, Kwapil, Wolfram, additional, Schön, Jonas, additional, Reiche, Manfred, additional, Savin, Hele, additional, Yli-Koski, Marko, additional, Sans, Juan Angel, additional, Martinez-Criado, Gema, additional, Seifert, Winfried, additional, Warta, Wilhelm, additional, and Weber, Eicke R., additional

Published
2009
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40. Impact of phosphorus gettering parameters and initial iron level on silicon solar cell properties.

Author

Vähänissi, Ville, Haarahiltunen, Antti, Talvitie, Heli, Yli ‐ Koski, Marko, and Savin, Hele

Subjects
PHOSPHORUS, NONMETALS, SOLAR cells, SEPARATION (Technology), SOLAR batteries
Abstract

ABSTRACT We have studied experimentally the effect of different initial iron contamination levels on the electrical device properties of p-type Czochralski-silicon solar cells. By systematically varying phosphorus diffusion gettering (PDG) parameters, we demonstrate a strong correlation between the open-circuit voltage ( Voc) and the gettering efficiency. Similar correlation is also obtained for the short-circuit current ( Jsc), but phosphorus dependency somewhat complicates the interpretation: the higher the phosphorus content not only the better the gettering efficiency but also the stronger the emitter recombination. With initial bulk iron concentration as high as 2 × 1014 cm−3, conversion efficiencies comparable with non-contaminated cells were obtained, which demonstrates the enormous potential of PDG. The results also clearly reveal the importance of well-designed PDG: to achieve best results, the gettering parameters used for high purity silicon should be chosen differently as compared with for a material with high impurity content. Finally we discuss the possibility of achieving efficient gettering without deteriorating the emitter performance by combining a selective emitter with a PDG treatment. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Published
2013
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41. Modeling and Optimization of Internal Gettering of Iron in Silicon

Author

Haarahiltunen, Antti, Väinölä, Hele, Yli-Koski, Marko, Sinkkonen, Juha, and Anttila, Olli

Abstract

We present a model for heterogeneous precipitation of iron in silicon. In the model Fokker-Planck Equation is used to simulate the evolution of size distribution of iron precipitates. From the simulation results we may conclude, that in case of low levels of initial iron concentration (<1×1012 cm-3), internal gettering is difficult to achieve just by cooling. The low level of initial iron concentration can be gettered by using an additional nucleation step, which can be just a fast ramp to room temperature, before isothermal gettering anneal. We also analyze the effect of competitive gettering on the final iron concentration and the iron precipitate density profile. We found that internal gettering can reduce iron concentration and the particular advantage is the reduction of the iron precipitate density in the device layer. The iron precipitation in the device layer can also be reduced by increasing the doping concentration as the segregation increases.

Published
2006
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