In this work, a study of low dimensional germanium (Ge) island on silicon substrate (Si) for visible metal semiconductor metal (MSM) photodetector was presented. The study was carried out using Silvaco ATLAS device simulator. Three Ge islands were designed such as big Ge, small Ge and combination Ge. Bulk Ge is also added for comparison. The structure of the island was constructed at the beginning of Atlas simulation and continued for simulation of MSM photodetector. From the structure, the energy band gap of the material was extracted whereby altering the Ge island sizes has altered the energy bands. The performance of the Ge island on Si as MSM photo detector was evaluated by dark and photo current – voltage (I-V) characteristics. It was found that the Ge island on Si significantly enhanced the current gain (8 times) compared to the bulk Ge. The combination Ge island MSM photo detector exhibited the highest gain and response towards visible light among the three islands.