Abstract:
The fundamental and technological importance of the group III-nitride
materials can not be overstated, due to their exciting structural and bandstructure properties. These materials have been used widely in applications such as optoelectronics, high-frequency and high-power electronics,
photovoltaics and sensing, to name a few. Because of thermodynamic constraints, it is not easy or cheap to produce large scale good quality single
crystals of AlN, GaN and InN, and due to unavailability of native substrates one is forced to grow them on foreign substrates. The mismatch
of the lattice parameters and thermal expansion coefficients between the
substrate and the overlayer leads to the generation of point and extended
defects and residual strain in the films. Nanostructuring III-nitride films
can help alleviate some of these issues and can also be used to enhance and
tailor the properties of the material because of the novel properties that
arise due to the low-dimensionality.
The systematic work in this thesis helps us understand the enhanced
luminescence and superior transport properties of GaN nanowall network
along with observation of room temperature ferromagnetic properties by
correlating these with experimentally derived electronic band-structure,
and quantum mechanical effects. Due to its unique morphology, polarisation induced spontaneous formation of 2DEG is possible and it determines
many of the transport properties. To further understand how the unique
structure of nanowall network influences its properties, comparative studies with low-dimensional nanorods, and flat or porous thin films have been
carried out.
In this thesis, we carry out comparative studies of GaN thin films and
one and two-dimensional nanostructures to understand the effect of defects
and low-dimensionality on the properties of the material. The work has
been divided into seven chapters described as follows.
