Semiconductor nanostructures and, in particular, quantum dots (QDs) have been
at the forefront of solid-state research for several decades and represent attractive
candidates for applications in quantum information and spintronics. QDs are characterised
by their quasi-three-dimensional quantum confinement of electrons and
holes which results in an ‘artificial-atom’ like structure with discrete but accessible
energy levels. In addition, the spin of carriers in QDs are relatively isolated
from typical spin relaxation mechanisms. This thesis investigates the spin physics
of self-assembled InAs/GaAs QDs grown by molecular beam epitaxy. The design
and growth of QD structures is described and it is shown how spin effects may be
investigated using circularly polarised (CP) light. This work demonstrates how spin
physics may be resolved through analysis of the emission polarisation of a QD ensemble.
In particular, a slope in the polarisation spectrum induced by CP excitation
is shown to correlate with a splitting between polarisation states of the QDs. This
idea is developed to create a new technique capable of resolving spin splittings far
narrower than the ensemble inhomogeneous linewidth. The technique is validated
by resolving Zeeman splitting, allowing g-factors and QD fine-structure effects to
be measured. The sensitivity to external magnetic field and the dynamics of the
optically induced polarisation splitting are investigated. A novel QD spin memory
is demonstrated with a long lifetime consistent with dynamic nuclear spin polarisation (DNSP). However, a rapid initialisation of the effect contradicts the traditional
understanding of DNSP and may open the door to new spin physics in QDs. A
connection is demonstrated between the polarisation splitting and the phenomenon
of negative circular polarisation (NCP). It is shown that NCP, previously only observed
in n-doped QDs, is in fact a general property of all QDs regardless of doping
level, calling into question the currently accepted generation mechanism.