Structural and electronic properties of monolayer and multilayer gallium nitride crystals
Author
Önen, Abdullatif
Advisor
Durgun, Engin
Date
2016-09Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Three-dimensional (3D) Gallium Nitride (GaN) is a III-V compound semiconductor
with direct band gap. It is widely used in light emitting diodes (LED)
and has potential to be used numerous optoelectronic applications. In this thesis,
rstly 3D GaN in wurtzite and zincblende structures are revisited and structural,
mechanical, and electronic properties are studied and compared with the literature.
Next, the mechanical and electronic properties of two-dimensional (2D)
single-layer honeycomb structure of GaN (g-GaN), its bilayer, trilayer and multilayer
van der Waals solids are investigated using density functional theory. Based
on phonon spectrum analysis and high temperature ab initio molecular dynamics
calculations, rst it is showed that g-GaN is stable and can preserve its geometry
even at high temperatures. Then a comparative study is performed to reveal how
the physical properties vary with dimensionality. While 3D GaN is a direct band
gap semiconductor, g-GaN in 2D has relatively wider indirect band gap. Moreover,
2D g-GaN displays higher Poisson's ratio and slightly less charge transfer
from cation to anion. It is also showed that the physical properties predicted
for freestanding g-GaN are preserved when g-GaN is grown on metallic, as well
as semiconducting substrates. In particular, 3D layered blue phosphorus being
nearly lattice matched to g-GaN is found to be an excellent substrate for growing
g-GaN. Bilayer, trilayer and van der Waals crystals can be constructed by special
stacking sequence of g-GaN and they can display electronic properties which can
be controlled by the number of g-GaN layers. In particular, their fundamental
band gap decreases and changes from indirect to direct with increasing number
of g-GaN layers. It is hoped that the present work will provide helpful insights
for growing g-GaN which can be widely used in nanoelectronics applications in
low dimensions.
Keywords
Two-dimensional (2D) materialsGallium nitride (GaN)
First principles simulations
Density functional theory (DFT)