Abstract:
Gallium Arsenide (GaAs), an outstanding member of the III-V semiconductor family with larger
and direct band gap enable transistors made of GaAs preferred compared to silicon. The
problem of computationally understanding properties of such materials goes down to solving
Schrödinger equation of a collection of mobile nuclei and electrons. Thus, DFT the most
successful method that forms the basis for advanced ab initio calculations was employed. Being
motivated by the promising role of GaAs in future technology and the DFT contribution in
computational material science, the researcher was determined to study the structural,
electronic, optical, mechanical and thermal properties of GaAs using DFT. In selecting suitable
DFT software, the researcher opted for open-source plane-wave DFT code – Quantum
ESPRESSO. The lattice parameter of GaAs was calculated using GGA-PBE and LDA, both are
in a better agreement to the experimental value. The band gap of GaAs calculated using LDA is
much better than GGA in approaching the experimental value. From the DOS and PDOS
calculation, a strong covalent bonding between Ga and As is observed. The optical properties of
GaAs have been investigated in the photon energy range 0 to 25eV. Maximum values of real and
imaginary part dielectric constant, refractive index, extinction coefficient, absorption coefficient
have been observed; and are all in good agreement with theoretical values. The calculated
elastic constants indicate GaAs is mechanically stable at ambient condition. The phonon DOS
and the corresponding phonon dispersion relation were calculated within temperature range of
0K to 300K. The maximum numbers of branches is six and are displayed at K point. The
temperature dependencies of vibrational energy, free energy, entropy and heat capacity of GaAs
were calculated within room temperature and all are fairly in good agreement with experimental
values.
