Low-dimensional semiconducting materials for next-generation nanoelectronics

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2016-12-09
Degree programme
83 + app. 49
Aalto University publication series DOCTORAL DISSERTATIONS, 259/2016
This thesis focuses on the fabrication and characterisation of silicon nanocrystal (SiNC), and two-dimensional gallium chalcogenides, namely, gallium selenide (GaSe) and gallium telluride (GaTe) for next-generation nanoelectronics and nanophotonics applications.  In the first part, silicon nanocrystal (SiNC)-based thin-film devices have been fabricated, where the idea of scaling down of channel length was implemented in such a way that very few SiNCs can be fitted inside the channel in the channel length direction in order to decrease the number of barriers to increase electrical conductivity. In this study, we have demonstrated the scaling down of channel length to 20 nm in order to reduce the number of barriers provided by each of the SiNCs, which are fabricated using a very high-frequency (VHF) plasma-enhanced chemical vapour deposition (CVD) system with a diameter of 10 ±1 nm. A high electrical conductivity has been achieved by optimising channel length. In addition, we have demonstrated the surface nitridation of SiNCs to protect the highly reactive surface of SiNCs from further native oxidisation and successfully suppressed the degradation of transport properties.  In the second part, we report on the nonlinear optical properties of few-layer GaTe studied by multiphoton microscopy. Second and third harmonic generation from few-layer GaTe flakes were observed in this study with the laser pump wavelength of 1560 nm. These processes were found to be sensitive to the number of GaTe layers. The second- and third-order nonlinear susceptibilities of 2.7 x 10-9 esu and 1.4 x 10-8 esu were estimated, respectively.  In the third part, we have established Raman fingerprint of GaTe and GaSe to investigate their crystal quality. Unencapsulated GaTe (GaSe) oxidises in ambient conditions which are well detected in their Raman analysis. X-ray photoelectron spectroscopy (XPS) analysis of GaTe (GaSe) shows a good agreement with Raman analysis. 50 nm-thick Al2O3 deposited by atomic layer deposition (ALD) to encapsulate GaTe (GaSe) inhibits degradation in ambient conditions.
Supervising professor
Lipsanen, Harri, Prof., Aalto University, Department of Micro- and Nanosciences, Finland
Thesis advisor
Riikonen, Juha, Dr., Aalto University, Department of Micro- and Nanosciences, Finland
2D materials, graphene, gallium selenide, gallium telluride, Raman, multiphoton microscopy, atomic layer deposition, silicon nanocrystals
Other note
  • [Publication 1]: Susoma Jannatul Ferdous, Yoshifumi Nakamine, Tetsuo Kodera, Koichi Usami, Yukio Kawano and Shunri Oda. Channel length scaling and surface nitridation of silicon nanocrystals for high-performance electron devices. Japanese Journal of Applied Physics, 52, 04CH08-1, 2013.
    DOI: 10.7567/JJAP.52.04CH08 View at publisher
  • [Publication 2]: Jannatul Susoma, Lasse Karvonen, Antti Säynätjoki, Soroush Mehravar, Robert A. Norwood, Nasser Peyghambarian, Khanh Kieu, Harri Lipsanen, and Juha Riikonen. Second and third harmonic generation in few-layer gallium telluride characterized by multiphoton microscopy. Applied Physics Letters, 108, 073103, 2016.DOI: 10.1063/1.4941998
  • [Publication 3]: Wonjae Kim, Changfeng Li, Ferney A. Chaves, David Jiménez, Raul D. Rodriguez, Jannatul Susoma, Matthias A. Fenner , Harri Lipsanen, and Juha Riikonen. Tunable graphene-GaSe dual heterojunction device. Advanced Materials, 28, 1845-1852, 2016.
    DOI: 10.1002/adma.201504514 View at publisher
  • [Publication 4]: Jannatul Susoma, Jouko Lahtinen, Mariia Grigoreva, Harri Lipsanen, and Juha Riikonen. Crystal quality of two-dimensional gallium telluride and gallium selenide using Raman fingerprint. Applied Physics Letters, 2016.