A thin dielectric layer plays a significant role to extend the electronic and optical properties of graphene-based field effect transistors. This study investigates the interaction between graphene and aluminum oxide layer (Al2O3) and the influence of Al2O3 on the properties of graphene. The electrical characterization demonstrates the tunability in the resistivity of Al2O3/Gr devices by applying V-g. Al2O3 deposition introduced n-doping in graphene and is affirmed by shifting of charge neutrality point towards negative V-g. The selective coverage of channel, results in the formation of p-n junction within graphene FET which becomes more pronounced upon DUV treatment. Moreover, the study validates the modulation in interface properties of pristine GFET and Al2O3/Gr at different V-g and temperatures. An enhancement in the intervalley and phase coherence scattering rates is observed for Al2O3/Gr device. Therefore, the effect of dielectric layer on graphene based field effect transistors would be of great interest to tune the properties the device.