This thesis presents an experimental investigation on the performance enhancement of graphene/silicon based near-infrared Schottky photodiodes. The photodiode devices were fabricated by transferring CVD graphene layers onto n-type silicon (n-Si) substrates. The samples exhibited strong Schottky diode character and had high spectral sensitivity at 905 nm peak wavelength. The Schottky contact characteristics of the samples (e.g., barrier height, ideality factor and sheet resistance) were determined by analyzing the current-voltage measurement data. All the samples demonstrated a clear photovoltaic activity under light illumination. The Schottky barrier height (SBH) in Gr/n-Si photodiodes was tuned as a function of light power density. Light power density driven modification of the SBH was correlated with the variation in the measured open-circuit voltage. The impact of junction area and number of graphene layers on the spectral responsivity and response speed of Gr/n-Si based Schottky photodiodes were also investigated. Firstly, three batches of Gr/n-Si photodiode samples with junction area of 4 mm2, 12 mm2 and 20 mm2 were produced by transferring monolayer CVD graphene on individual n-Si substrates. The sample with 20 mm2 junction area reached a spectral response of 0.76 AW-1, which is the highest value reported in the literature for self-powered Gr/n-Si Schottky photodiodes without the modification of graphene electrode. In contrast to their spectral responsivities, the response speed of the samples was found to be lowered as a function of the junction area. After that, we increased the number of graphene layers on n-Si. Wavelength-resolved and time-dependent photocurrent measurements demonstrated that both spectral responsivity and response speed are enhanced as the number of graphene layers is increased from 1 to 3 on n-Si substrates. This thesis showed that the device performance of Gr/n-Si Schottky photodiodes can be modified simply by changing the size of graphene electrode and/or as well as the number of graphene layers on n-Si without need of external doping of graphene layer or engineering Gr/n-Si interface.