Abstract:
Recent simulation study shows that a considerable and stable band gap can be opened in
2D materials by applying biaxial strain. But a systematic study on the effect of biaxial
strain on band gap and other important material electronic parameters are still missing in
literature. In this thesis, the structural and electronic properties of various configurations
of graphene/hexagonal Boron Nitride hetero bilayer (C/h-BN HBL) system has been
investigated using density functional theory (DFT) under local density approximation
(LDA).Biaxial strain has been applied on this material and its effect on electronic band
structure and properties derived from band structure such band gap, carrier effective
mass, Fermi velocity have also been simulated. This work reveals that irrespective of
the application of biaxial strain it remains direct and hence can be exploited in
optoelectronic applications. Also, it has been observed that the band gap increases
monotonically (29.7meV-113.4meV) from compressive to tensile strain region. The
electron effective mass (0.003732me-0.024902 me) and hole effective mass (0.003747
me-0.023888 me) also increases from compressive to tensile strain region. But Fermi
velocity for both electron (1.257278×106 m/s-0.3866997×106 m/s) and hole
(1.265725×106 m/s-0.3816452×106 m/s) shows an opposite trend. From density of
states (DOS) it is clear that this material system shows a linear trend in lower energy
region as observed in pristine graphene. Band structure calculation shows an almost
linear dispersion relationship at Dirac point which predicts the Fermion like
characteristics of electrons in this material system. Finally, biaxial strained materials
were implemented in the channel of a top gate ballistic MOSFET and device
performance was investigated using non-equilibrium Green’s function (NEGF) coupled
with DFT. The results show that for lower band gap material the transport lacks
saturation region which is crucial for stable operation of transistors in logic circuits. It is
also obvious from the results that carrier effective mass and Fermi velocity has
negligible effect on drive current. Ultimately, an optimum channel material (12% tensile
strained B3 configuration) was proposed and implemented in the channel of MOSFET.
Better device performance with current saturation has been observed with this proposed
material.
