Development of electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs).

In this thesis design, development and realisation of a substrate emission
electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs)
emitting in the 980 nm wavelength range is discussed. Chapter 1 provides a
literature review of the relevant VCSEL and (OP-VECSEL) technology required
for the design of an EP-VECSEL. In chapter 2, different areas of the device design
are highlighted, including electrical and optical performance of the distributed
Bragg reflectors (DBRs), active region design, device detuning and antirefiective
coating design.
Chapter 3 provides a description of the method used to fabricate EP-VECSEL
devices and focuses on optimisation of different process steps, namely the trench
etch profile and depth, as well as the contact metalisation. A method for
characterising the detuning of a wafer is also presented. In chapter 4
measurements of fabricated EP-VECSEL are presented, with a method for the
characterisation of the EP-VECSEL material by modulating the output coupler
mirror reflectivity demonstrated. This method is then used to examine the affect
of different substrate dopings on device performance. Data is also presented on
beam quality, power scaling and thermal properties.
Chapter 5 investigates methods for improving electrical aspects of device
operation, with improved nand p DBR designs proposed. In addition, analysis of
SIMS data for an EP-VECSEL and n-DBR are presented, along with an
investigation of the top contact geometry. In chapter 6 a discussion of the QW
active region is provided, first by analysing the epitaxial material used in chapter
4 and then proposing improvements to the growth process. A comparison of a 3,
6 and 9 QW active region is then presented, where the trade offs in the optimum
number of QWs are examined. Finally, this thesis is summarised and a new
device design is proposed from the findings.