This work has been motivated by the outstanding need to prepare suitable substrate for growth of III-nitride heteroepitaxial thin films. The issue of lattice and thermal expansion mismatches between the substrates and overlayers, which results in a high threading dislocation density in the films, is seen to be detrimental to photon and carrier transport in these systems. Thus, looking for appropriate substrates or modifying substrates appropriately, has attracted enormous attentions. The work includes the chemical and structural modifications of silicon, gallium arsenide and sapphire substrates, to obtain appropriate characteristics. The work also consists of a significant portion on the adsorption and desorption characteristic of Ga metal on various high and low index silicon surfaces. This study not only complements the search for substrate for GaN growth, but also in other interesting aspects of initial stages of metal/semiconductor interface formation, evolution of superstructural 2D- surface phases and formation of sub-nanodimension metal nanostructures and delta doped.