This thesis aims to investigate thermodynamic properties and epitaxial processes at the very early stages of GaP on Si heterogeneous growth for photonics and energy applications. The absolute {001}, {136}, {114} surfaces energies and abrupt and compensated interface energies of the GaP/Si material system are first determined by density functional theory (DFT) calculations. Furthermore, we studied the wetting properties of the GaP/Si through the surface and interface energies computed by DFT. We found that the partial wetting (observed experimentally) is always achieved whatever the chemical potential, and that it is even favoured by the silicon surface passivation. Through free energy change calculations, we have shown that the surface and interface energies play a crucial role in the III-V/Si 3D- growth while the impact of elastic energy contribution on surface island morphology is negligible. These conclusions are generalized to the various III-V/Si systems. A general III-V on Si growth mechanism is finally proposed to clarify the very early stages of growth and the defect generation (such as antiphase domains) that fundamentally originate from the partial wetting of III-V on Si. Experimental studies have been performed to understand the influence of the initial silicon surface on the III-V overgrowth. Furthermore, preliminary studies on AlGaP markers efficiency on antiphase domains annihilation and a first characterization of their electrical properties are also presented. Finally, surface energy engineering was used to demonstrate a textured GaP template monolithically grown on silicon that could be used for photoelectrochemical water splitting applications.