Investigation of the Structural, Electronic, and Thermoelectric Properties of Mono-Chalcogenide

Student: Aida Sheibani

Degree: M.S., July 2020

Major Professor: Dr. Bothina Manasreh

Research Area(s):

Modeling & Simulation

Microelectronics

The limitation of fossil fuel resources has motivated scientists to search for a way to increase the efficiency of production while limiting the carbon dioxide emission.
Thermoelectric (TE) materials have drawn attention due to their applications in converting wasted heat into electric current without producing pollution.

For studying structural and electronic properties of GeTe, GeS, and GeSe the DFT calculation was used.
The thermoelectric properties were calculated using semi-classical Boltzmann transport theory using BoltzTrap code.
To investigate the stability of the structure in GeTe, the phonon dispersion and second order harmonic interaction force constants were calculated.
The elastic constants matrix was used for studying stability of doped GeS, and GeSe.

Showing the effect of polar distortion on electronic, transport properties, and lattice thermal conductivity of GeTe.
Clarifying the structural transformation by introducing dopant to GeS and GeSe .
Describing the changes in band structure, due to presence of dopant.

The rhombohedral structure is the ground state structure for GeTe, which has an indirect band gap of 0.55 eV.
Polar structures with higher polarization tend to show higher thermoelectric efficiencies.
The ground state structure for GeS and GeSe is orthorhombic and the band gaps were found to be direct in the case of GeS and indirect for GeSe with values of 1.23 eV and 0.82 eV, respectively.
The figure of merit is found to decrease upon doping with group III, IV, V, VI of the GeSe alloy by 33% and 26% at 300 K and 600 K, respectively