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7. 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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8. 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

9. 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

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