I would like to gratefully acknowledge the enthusiastic supervision of Dr. Ali Rezazadeh during this work. I thank Prof. Garth Swanson for the technical discussions on the spectral response model and Dr. S. E. Kanellopoulos for the help with optical measurements and relevant discussions. Postgraduates of the Physical Electronics Research Group are thanked for numerous stimulating discussions, help with experimental setup and general advice; in particular I would like to acknowledge the help of Dr. Jim Luck for his support. Sean Wootton, Kevin Smith and Nick Nicola are thanked for their assistance with all types of technical problems - at all times.
I am grateful to all my friends from International Hall, University of London, for being the surrogate family during the many years I stayed there and for their continued moral support there after. From the staff, Donald Mann and Margaret Wilson are especially thanked for their care and attention.
Finally, I am forever indebted to my parents and Anita for their understanding, endless patience and encouragement when it was most required. I am also grateful to Naela and Tanvir for their support.