Influence of neutral region on the low frequency (100 Hz to 1 MHz) optical signal response of planar molybdenum/n-type silicon/molybdenum structures with Schottky barriers at both ends has been investigated. It is found that the presence of the neutral region under optical illumination can enhance the device signal current and the spectrum of increment in the signal current exhibits a low turn-over frequency due to its diffusion mechanism. An equivalent circuit representation of such a structure has also been proposed.