Graphene three-terminal nanojunction rectifiers

PhD disertation of Pascal Butti (2017)

Intrinsic voltage rectification in graphene three-terminal junctions (GTTJs) is investigated, with the goal to advance understanding of physical mechanisms behind this effect. In the first part, finite element simulations based on a field-effect transistor model are made to calculate output-voltage characteristics for realistic diffusive GTTJs. Within this model, rectification is described as an electrostatic effect. The simulations fit well to a substantial number of reported experimental results and provide engineering guidelines for rectification efficiency enhancement, such as good graphene material quality and high capacitive gate coupling. According to the simulations, efficiency in diffusive GTTJs is intrinsically limited to around 60%, as a consequence of the inability to pinch off conductivity in graphene. In the second part, etched GTTJs of different sub-micron constriction widths (down to 100 nm) are fabricated on Si/SiO₂ substrates and characterized electrically at 296 K and 87 K. Reproducibility of the rectification effect is demonstrated. Typical room-temperature rectification efficiencies are 10 to 20% at 100 mV input voltage, whereas efficiencies at 87 K are below 10%. The highest room-temperature rectification efficiency measured in our devices is ~40% (at 400 mV input voltage), which is higher than most efficiencies reported in the literature. Experiments show higher efficiencies at room temperature than at 87 K, in contrast to the predictions of the field-effect simulations. This indicates that mechanisms other than the field effect contribute to the rectification effect.

References:

[1] A. Jacobsen, I. Shorubalko, L. Maag, U. Sennhauser, and K. Ensslin "Rectification in three-terminal graphene junctions", Appl. Phy. Lett., 97, 032110 (2010)

[2] P. Butti, I. Shorubalko, U. Sennhauser, and K. Ensslin "Finite element simulations of graphene based three-terminal nanojunction rectifiers", J. of Appl. Phys. 114, 033710 (2013)

[3] P. Butti, R. Brönniman, K. Ensslin, and I. Shorubalko "Joule-heating induced thermal voltages in graphene three-terminal nanojunctions", Appl. Phys. Lett., 112, 133501 (2018)

 

Miniaturized spectrometers 

Surface optical waveguides in combination with subwavelength light scatterers proved to be a promising method for constructing miniaturized spectrometers.

[1] E. Zgraggen, O. Scholder, G. L. Bona, F. Fontana, E. Alberti, A. Crespi, R. Osellame, T. Scharf, and I. Shorubalko "Optical properties of waveguide-coupled nanowires for sub-wavelength detection in microspectrometer applications" J. Opt., 17, 025801 (2015)

[2] M. Madi, F. Ceyssens, I. Shorubalko, H. P. Herzig, B. Guldimann, P. Giaccart "Lippmann waveguide spectrometer with enhanced throughput and bandwidth for space and commercial applications" Optics Express, 26, 2682 (2018)

[3] M. Madi, E. Alberti, I. Shorubalko “Miniaturized Waveguide Imaging Spectrometer” European Patent Application EP3270127, Patent Cooperation Treaty Application WO2018011035, Filed: 15.07.2016, Published: 17.01.2018