n - Çukurova Üniversitesi

ABSTRACT
PhD. THESIS
ELECTRONIC AND OPTICAL PROPERTIES OF SbSI:
APPLICATION OF DENSITY FUNCTIONAL THEORY
Harun AKKUŞ
DEPARTMENT OF PHYSICS INSTITUE OF NATURAL AND
APPLIED SCIENCES UNIVERSITY OF CUKUROVA
Supervisor: Prof. Dr. Emirullah MEHMETOV
Year: 2007, Page: 113
Jury: Prof. Dr. Emirullah MEHMETOV
Prof. Dr. Bahşeli İ. GULİYEV
Prof. Dr. Birgül YAZICI
Prof. Dr. Bekir ÖZÇELİK
Prof. Dr. Metin ÖZDEMİR
In this dissertation, the electronic and optical properties of ferroelectricsemiconductor
SbSI crystal have been investigated by using the density functional
theory (DFT) and ab-initio pseudopotential method within the local density
approximation (LDA) in a wide temperature region include paraelectric and
ferroelectric phases. It has been shown that SbSI crystal has an indirect band gap in
both phases (1.45 eV and 1.49 eV in the paraelectric and ferroelectric phases,
respectively) and that the smallest direct band gap (1.56 eV and 1.58 eV in the
paraelectric and ferroelectric phases, respectively) is at the S high symmetry point of
the Brillouin zone. Furthermore, it is shown that the phese transition, from
o
paraelectric phase to ferroelectric phase (the transition temperature is about 22 C ),
does not change the nature of the band gap. The total density of states (DOS) of SbSI
crystal have been calculated in the paraelectric and ferroelectric phases. The linear
photon-energy dependent dielectric functions and some optical constants such as the
absorption coefficient, extinction coefficient, refractive index, energy-loss function,
reflectivity and optical conductivity are calculated in both phases. The effective
number of valence electrons and the effective optical dielectric constant are also
calculated for both phases. Moreover, some components of second-order photonenergy
dependent susceptibility tensor of SbSI crystal are calculated in the
ferroelectric phase.
Key Words: SbSI, ferroelectric-semiconductor, electronic structure, optical
properties, density functional theory.
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