This work is a contribution to the investigation of the spin properties of III-V semiconductors with possible applications to the emerging semiconductor spintronics field. Two approaches have been explored in this work to achieve a long and robust spin polarization: i) Spatial confinement of the carriers in 0D nanostructured systems (quantum dots). ii) Defect engineering of paramagnetic centres in a bulk systems. Concerning the first approach, we investigated the polarization properties of excitons in nanowire-embedded GaN/AlN quantum dots. We evidence a sizeable and temperature insensitive linear polarization degree of the photoluminescence (~15 %) under quasi-resonant excitation with no temporal decay during the exciton lifetime. A detailed theoretical model has also been developed to account for the observed results. Regarding the second approach, we demonstrated a proof-of-concept of conduction band spin-filtering device based on the implantation of paramagnetic centres in InGaAs epilayers. This approach relies on the creation of Ga interstitial defects in dilute nitride GaAsN compounds and it overcomes the limitations inherent to the introduction of N in the compounds.