| Summary: | Using the techniques of scanning tunnelling microscopy and spectroscopy (STM/STS), the structural and electrical properties of silicon on clean cleaved GaAs(110) surfaces were investigated on a nano-meter scale. This work was focused on the effect of cleaving-induced defects on GaAs(110) surface, the resultant silicon formation and the electrical properties of the overlayer/substrate system formed at 280°C. Localised I-V measurements, performed using STS, on atomic step defects of GaAs(110) surfaces showed a Fermi-level shifted ~0.5 and 0.8 eV towards mid-gap position for both n- and p-type substrates respectively. However, measurements taken from silicon-coated atomic steps showed that the Fermi-level reverted back towards its 'ideal' flat band position by ~0.4 eV for both substrates. Similar shifts were also observed on silicon-free as well as coated defect clusters. This behaviour was distinctively different to silicon adsorbed at defect-free surfaces. Hence, these results clearly indicated passivating properties of silicon on the defective surfaces of GaAs(110) when deposited under these conditions. Such observations were also in good agreements with results obtained on macroscopic scale using x-ray photoelectron spectroscopy (XPS). STM images obtained at submonolayer silicon coverages showed preferential adsorption of silicon nanoislands at the defective sites. This suggested that the elevated temperature growth of silicon together with the excess dangling bonds associated with the defects, provided enhanced thermodynamic conditions to induce ordered silicon growth at the surface defects and effectively mopped up the dangling bonds associated with the defects, provided enhanced thermodynamic conditions to induce ordered silicon growth at the surface defects and effectively mopped up the dangling bonds. Implications of this work for use in laser facet are discussed in this thesis. Finally, this project ended with the study of 'real' laser devices using cross-sectional STM/STS techniques. The layered laser structure, which made up of different semiconducting materials, was evident from the cross-sectional STM images. Very often, atomic steps were seen at the active region of the cleaved facets which suggested the importance of facet passivation.
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