Metal-Oxide Semiconductor (MOS)nanostructures have a potential future prospect large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications. The fabrication and design of photodetectors or optical switches based on nanostructures with different morphology, suitable choice of substrate with different growth techniques have shown rapid advancement in past few years. Nanostructure photodetector can be designed in different ways either based on the device structure or based on mechanism of photoconduction. Possibly the most simple type of device structure is metal semiconductor metal (MSM) type which can be operated based on resistive nature of the materials whose conductions are modulated by generation of electron-hole pairs in presence of excitation by suitable frequency of photon and its transportation in external circuit. Photodiodes, avalanche photodiodes (APD), phototransistors and Photo multiplier tube(PMT) type complex device architecture with high end fabrication techniques are being used for high speed applications in communication systems. Apart from high end fabrication techniques like chemical vapour deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD) and use of different substrates, techniques like design of hetero structure devices, doping the active material with suitable elements, surface modification of the active materials and integration of closely spaced inter-digtated electrodes have been employed for the enhancement of the performance of the device.