Investigation of M.B.E. Grown GaAs - Si Heterostructures for Optical Monolithic Integration.

The field of monolithic optoelectronic structures has been critically reviewed resulting in the proposal for new structures based on a comprehensive study of GaAs/Si heterostructures. The underlying theory of electro-optic effects which these optical devices are based on has been discussed leading to proposals for various alternative configurations (co-planar, longitudinal and transverse) and investigations of their modulation and switching properties in relation to orientation, at a wavelength of 905nm. A detailed consideration of the epitaxial layer properties and related contact metallisation together with the required optical setup was necessary for these investigations. The MBE system and for contact metallisation the sputter deposition system have been utilised under specific experimental requirements. The results of the studies indicate that; 1) A two-step MBE growth procedure incorporating a strain layer under unique annealing conditions provide good GaAs layers on Silicon with very smooth texture and uniform layers. Electrical characterisation of the heterostructures with strain layer show better switching conditions and low interface state densities. 2) Molybdenum provides excellent contacts on both silicon and GaAs and can be utilised for monolithic devices. 3) Good modulation and switching is achieved with the electrode configuration playing a crucial role in the reduction of the applied electrical bias. (97% less). 4) Misoriented substrates, (2°,3°and 4°off (100)) do not significantly change the modulation results and hence can be utilised during layer fabrication to significantly reduce the interface defects and grow better GaAs/Si heterostructures.