Abstracts Book - IMRC 2018

• SA6-P011
DIELECTRIC FUNCTION AND EXCITON TRANSITIONS IN ALD
GROWN WSe2 MONOLAYER
Won Chegal 1 , Jun Oh Kim 2 , Sang Jun Lee 2 , Sang Woo Kang 1 , Mangesh Diware 1
1 Korean Research Institute of Standards and Science, Advanced Instrumentation Institute,
South Korea. 2 Korean Research Institute of Standards and Science, Division of Industrial
Metrology, South Korea.
Two-dimensional (2D) materials, like transition metal dichalcogenides (TMDCs),
are fascinating semiconductors with exotic physical, optical, electrical, and
mechanical properties, open unique opportunities for fundamental physics and
novel applications. The optical behavior of TMDCs are dominated by strong
many-body interactions such as electron-hole pairs – excitons, charged excitons
– trions, and bound excitons – biexcitons, needs proper understanding the
scientific and technological standpoint. There are contradictory reports in the
literature about characterizing parameters of these quasiparticles, may be due
to the indirect determination. Here, exciton band structure of WSe2 monolayer
is investigated using spectroscopic ellipsometry. It is found that WSe2 monolayer
have indirect band gap at 2.26 eV and the binding energies of ground states of
two so-called A and B excitons are 0.71 eV and 0.28 eV. Energy positions of first
three excited excitonic states are determined, which show deviation hydrogenic
Rydberg series. Non-hydrogenic behavior suggests that each excitonic state
experience different dielectric environment, which generates the non-local
Coulomb interactions in 2D materials. These results will shed some light to
improve the correlation between theoretical predictions and experimental
results, which will be useful for next-generation applications and to get the
critical insight of fundamental physics.
Keywords: ellipsometry, dielectric function, WSe2
Presenting authors email: wchegal@kriss.re.kr