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Amira Ben Gouider Trabelsi
Amira Ben Gouider
Trabelsi
Feodor Kusmartsev
Feodor
Kusmartsev
Marat Gaifullin
Marat
Gaifullin
Derek Michael Forrester
Derek Michael
Forrester
Anna Kusmartseva
Anna
Kusmartseva
M. Oueslati
M.
Oueslati
Morphological imperfections of epitaxial graphene: from a hindrance to the generation of new photo-responses in the visible domain
Loughborough University
2020
untagged
Physical Sciences not elsewhere classified
2020-01-20 15:08:14
Journal contribution
https://repository.lboro.ac.uk/articles/journal_contribution/Morphological_imperfections_of_epitaxial_graphene_from_a_hindrance_to_the_generation_of_new_photo-responses_in_the_visible_domain/9244832
We report the discovery of remarkable photo-physical phenomena with characteristics unique to epitaxial graphene grown on 6H-SiC (000-1). Surprisingly, the graphene electrical resistance increases under light illumination in contrast to conventional materials where it normally decreases. The resistance shows logarithmic temperature dependences which may be attributed to an Altshuler-Aronov effect. We show that the photoresistance depends on the frequency of the irradiating light, with three lasers (red, green, and violet) used to demonstrate the phenomenon. The counterintuitive rise of the positive photoresistance may be attributed to a creation of trapped charges upon irradiation. We argue that the origin of the photoresistance is related to the texture formed by graphene flakes. The photovoltage also exists and increases with light intensity. However, its value saturates quickly with irradiation and does not change in time. The saturation of the photovoltage may be associated with the formation of a quasi-equilibrium state of the excited electrons and holes associated with a charge redistribution between the graphene and SiC substrate. The obtained physical picture is in agreement with the photoresistance measurements: X-Ray photoelectron spectrometry "XPS", atomic force microscopy "AFM", Raman spectroscopy and the magnetic dependence of photo resistance decay measurements. We also observed non-decaying photoresistance and linear magnetoresistance in magnetic fields up to 1 T. We argue that this is due to topological phases, spontaneously induced by persistent current formation within graphene flake edges by magnetic fields.