@Misc{Supelec592,
author = {Babar Bashir},
title = {{Designing of High Reflectance Distributed Bragg reflectors (DBRs), mirrors using AlGaInN material system in the UV wavelength range}},
year = {2009},
month = {jun},
abstract = {Gallium Nitride (GaN) and its alloys with aluminum (AlxGa1-xN)
and indium (InyGa1-yN \& AlzIn1-zN) have gained lots of attention
in optoelectronics research community in the last decade. These
semiconductors relativity have a wide bandgap and easy to make
n-type layers by Si doping and p-type layers by Mg doping.
Consequently nitride alloys have proved to be very attractive
candidate for the fabrication of Distributed Bragg reflectors
(DBRs) for VCSEL including other optoelectronic devices.
Distributed Bragg reflectors have prime importance in the
performance of VCSEL. DBRs not only provide highest possible
reflectivity, usually 99.9% is required, but also conduct
electricity, confine current, to the gain region. That’s why
accurate modeling and simulation of DBRs have significant
importance for the future fabrication of VCSEL.
Matrix transmission method is employed to model and simulate the
nitride based DBRs. As refractive index and absorption
coefficient is key parameters to design optoelectronic devices
and necessary to model the DBRs are modeled. Refractive index is
modeled in this thesis work by Adachi’s model and Sellmeier model.
In first part of thesis, matrix transmission based DBR model is
implemented on AlxGa1-xN based DBRs. Refractive index is modeled
by Adachi’s model and Sellmeier model. As Adachi’s model is
widely considered most accurate model so it is used to calculate
the refractive index over the entire range mole fraction of Al
(Aluminum). Absorption is also modeled. Reflectivity spectrum is
plotted by AlGaN/AlGaN, AlGaN/GaN, AlN/GaN and AlGaN/AlN based
DBRs. Phase response and transmissivity also are plotted. The
bandwidth is an important parameter in nitride alloys. So how
bandwidth is influenced by number of parameters like
reflectivity, number of periods and Bragg wavelength are
analyzed. The bandwidth with and without dispersion is plotted.
Two design curves are plotted that are very useful to practical
realization of DBRs. These curves give us minimum operating
wavelength and minimum Al content in 2nd layers over the number
of periods.
In second part of thesis, InyGa1-yN alloy is investigated and try
to find hurdles to calculate accurate optical parameters e.g.
energy bandgap, refractive index and absorption coefficient.
Stress free InGaN/AlGaN DBRs are also modeled and their
reflection spectrum is plotted.
In third and last part of thesis, AlzGa1-zN alloy is investigated
and discussed obstacles to calculate its accurate optical
parameters. AlGaN/GaN lattice matched DBRs are also discussed
with details and reflection spectrum is plotted.
In conclusion, we demonstrated which nitride alloy is most
promising for designing and fabrication of DBRs in this date and
which one could be in future.}
}