In this thesis, we study the structural and optical properties of GaN-based material structures grown on silicon substrates by temperature-dependent Photoluminescence (PL)¡BRaman¡BXRD and time-resolved PL measurements. In non-intentionally doped GaN structure, various excitonic transitions near band edge are observed and identified. We estimate the stress of the GaN samples to be 0.671 Gpa and 0.57 Gpa by using the energy shift of neutral-donor-bound exciton transitions. This is consistent with our Raman measurements. According to the XRD patterns, the length of InGaN/GaN multiple quantum wells in samples D¡BE¡BF are 43.83 nm¡B65 nm and 68.27 nm. In these samples, multiple PL peaks at low temperatures are observed. Carrier recombination lifetime have been measured as well.