Analysis and optimization of an MSM photodetector based on thin polysilicon layer

The analysis and optimisation of a microphotonic structure for high speed and efficient optical detection of metal-semiconductor-metal (MSM-PD) type based on polysilicon thin layer as light absorption region is presented. The photoresponse of the MSM-PD is analyzed in dependence with material parameters and structure geometry for simultaneously optimization of the speed and responsivity. The results of the analysis have been applied for design and fabrication of a MSM-PD structure on polycrystalline silicon layer deposited by LPCVD on Si substrate covered with a SiO₂ layer. The thickness of this insulating layer was design to assure a high reflectance of unabsorbed light at the first path through the thin polysilicon layer. Advantages of a high bandwidth in the GHz range and a fabrication process compatible with conventional CMOS make this type of photodetector one of the most attractively for photonic integrated circuits.