Abstract
With the increasing demand for data-intensive applications, developing higher efficiency and
more thermally stable near-infrared semiconductor lasers is of significant interest for the future
of telecommunications. A key design consideration for these lasers is the temperature sensitivity
of both the output power and emission wavelength, which necessitates using energy-intensive
active cooling to stabilise device operation. Removing the need for active cooling would result
in improved wall-plug efficiency and reduce the complexity and cost of these devices. This
thesis explores the possibility of using new approaches to improve the temperature stability of
semiconductor lasers, such as the use of type-II active regions, in which the electrons and holes
are spatially separated, and by incorporating highly mismatched bismide and nitride alloys into
the active region.
GaInAs/GaAsSb type-II ""W""-lasers emitting at 1255 nm were first investigated. These demonstrated low room temperature threshold current densities around 200–300 A/cm2 and a reduced
thermal redshift of the emission wavelength around 0.31 nm/K. This reduced thermal redshift was
further investigated using temperature-dependent gain studies, supplemented by a comprehensive
modelling investigation, which together demonstrated the significant role of injection-dependent
electrostatic effects on the temperature sensitivity of type-II active regions. This also resulted in
the development of a general-purpose device modelling toolkit.
Beyond changing the geometry of the active region, highly mismatched bismuth-containing
alloys offer the possibility of suppressing intrinsic non-radiative Auger processes. In this thesis,
photoreflectance studies of bismide-nitride alloys were used to quantitatively determine the
compositions of both bulk and quantum well structures, and provided an improved understanding
of the growth constraints of these interesting alloys.
Finally, combining the activities on both novel heterostructures and materials, the prospect of
using ""W""-active regions to integrate dilute bismide and nitride alloys was explored, illustrating
how this approach could further extend the accessible wavelength range and work towards
mitigating the effects of unfavourable Auger losses on device performance.
Overall, these results provide an improved understanding of the unique factors and considerations
at play in type-II systems and highlight the prospect of exploiting these systems to design devices
with a tailored temperature sensitivity, which may lead to improvements in the overall efficiency
and thermal stability of near-infrared semiconductor lasers.