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Q-NET young researchers

Jonna Marika PAAJASTE
Laboratorio NEST: National Enterprise for nanoScience and nanoTechnology, CNR-SNS, Pisa, Italy



Diplomas, University(ies)
puce Master of Science in semiconductor physics (MSc) 2009, "The Fabrication of 2 µm GaSb-based Semiconductor Disk Lasers", Tampere University of Technology

Field of research
Molecular beam epitaxy, semiconductor heterostructures, optoelectronics, hybrid-superconductors, nanodevices

Research experience:
hjg 2006–2013 Molecular beam epitaxy growth and characterization of III-V semiconductor heterostructures for optoelectronic devices, Optoelectronics research centre, Tampere University of Technology, Tampere, Finland

hjg 2013– Study of spin-dependent effects in hybrid superconducting devices with semiconductor nanowires
Laboratory NEST, National Enterprise for nanoScience and nanotechnology, Pisa, Italy

Thesis Project :
PhD thesis study done in Finland:
GaSb-based optical vertical-cavity devices for mid-infrared applications

Inexpensive, compact lasers and detectors in the mid-infrared (2 µm < λ < 5 µm) region would be useful solution for various sensing and laser spectroscopy applications, in particular for the detection of atmospheric pollutants. The thesis aim is the development of devices for 2–3 µm wavelength range, where the antimonide (AlGaIn)(AsSb) alloys offer and excellent option. Focus is on semiconductor disk lasers (SDL) and semiconductor saturable absorber mirrors (SESAMs) for laser mode-locking. High power SDLs have nearly diffraction limited beam and the external cavity configuration enables the use of intra-cavity filters for wavelength tuning and SESAMs for ultra-fast pulse generation. SESAMs have been studied for other semiconductor material groups, but the technology is still new in the mid-infrared region. To expand the use of SESAMs also to this regime, material research is done and the possibilities for SESAM parameter control are explored.

Study related to Q-NET:
Study of spin-dependent effects in hybrid superconducting devices with semiconductor nanowires

The main focus is the nanodevices implemented with semiconductor nanowires (InAs, InAs/InP and/or InSb) contacted to superconducting electrodes. These nanowires are not superconducting but may acquire superconducting-like properties when in contact with a superconductor. Our aim is to investigate the role of the electron spin in superconductor/nanowire systems with nanowires of InAs and InSb, which are semiconductor alloys known to possess a large gyromagnetic factor and large spin-orbit interaction. It is therefore of great relevance to investigate the interplay between spin-dependent phenomena and the proximity effect in these materials. We investigate the samples at very low temperatures (down to 10 mK) also in the presence of magnetic field. The low-temperature magneto-transport measurements will allow us to understand the impact of Zeeman splitting and spin-orbit interaction existing in the nanowires with the Josephson coupling and proximity effect. This will enable the realization of exotic electronic states, and might put the basis for the investigation of Majorana fermions which are predicted to exist in such systems.

List of Publications
K. Yang, D. Heinecke, J. Paajaste, C. Kölbl, T. Dekorsy, S. Suomalainen, M. Guina,
”Mode-locking of 2 μm Tm,Ho:YAG laser with GaInAs and GaSb-based SESAMs”
Opt. Express. 21, 4, 4311–8 (2013)

J. Paajaste, S. Suomalainen, R. Koskinen, A. Härkönen, G. Steinmeyer, M. Guina, ”GaSb-based semiconductor saturable absorber mirrors for mode-locking 2 μm semiconductor disk lasers”, Phys. Status Solidi C 9, 2, 294–297, (2012)

J. Paajaste, J. Nikkinen, R. Koskinen, S. Suomalainen, O.G. Okhotnikov, ”Power scalable 2.5 µm (AlGaIn)(AsSb) semiconductor disk laser grown by molecular beam epitaxy”, J. Crystal Growth, vol. 323, 1, 454–456 (2011)

A. Härkönen, C. Grebing, J. Paajaste, R. Koskinen, J.-P. Alanko, S. Suomalainen, G.  Steinmeyer, M. Guina, “Modelocked GaSb disk laser producing 384 fs pulses at 2 µm wavelength”, Electr. Lett. 47, No. 7, 454–456 (2011)

A. Härkönen, J. Paajaste, S. Suomalainen, J.-P. Alanko, C. Grebing, R. KOskinen, G. Steinmeyer, M. Guina, ”Picosecond passively mode-locked GaSb-based semiconductor disk laser operating at 2 µm”, Opt. Lett. 35, No. 24, pp. 4090–4092 (2010)

K. Haring, J. Viheriälä, M.-R. Viljanen, J. Paajaste, R. Koskinen, S. Suomalainen, A. Laakso, K. Leinonen, T. Niemi, M. Guina, ”Laterally-coupled distributed feedback InGaSb/GaSb diode lasers fabricated by nanoimprint lithography”, Electron. Lett.46, No.16 (2010)

J. Paajaste, S. Suomalainen, R. Koskinen, A. Härkönen, M. Guina, M. Pessa, ”High-power and broadly tunable GaSb-based optically-pumped VECSELs emitting near 2 um”, J. Crystal Growth vol. 311, 1917–1919 (2009)

S. Kivistö, R. Koskinen, J. Paajaste, S.D. Jackson, M. Guina, O.G. Okhotnikov, ”Passively Q-switched Tm3+, Ho3+ -doped silica fiber laser using a highly nonlinear saturable absorber and dynamic gain pulse compression”, Opt. Express 16, 22058–22063 (2008)

J. Lyytikäinen, J. Rautiainen, S. Suomalainen, R. Koskinen, J. Paajaste, A. Härkönen, M. Guina, O.G. Okhotnikov, ”MBE grown optically pumped semiconductor disk lasers emitting at 940 nm” Mat. Sci. Eng. B vol. 147, 161–165 (2008)

S. Suomalainen, M. Guina, T. Hakulinen, R. Koskinen, J. Paajaste, M. Karjalainen, M. Saarinen, S. Marcinkevicius, O.G. Okhotnikov, ”Semiconductor saturable absorbers with recovery time controlled by lattice mismatch and band-gap engineering”, Mat. Sci. Eng. B vol. 147, 156–160 (2008)

Pb/InAs nanowire Josephson junction with high critical current and magnetic flux focusing, J. Paajaste,  M. Amado, S. Roddaro, F. S. Bergeret, D. Ercolani, L. Sorba, and F. Giazotto, Nano Letters 15/3, 1803-1808 (2015).

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