Study On Breakdown Characteristics And Linearity Of Avalanche Photodiodes

In this paper,models of avalanche photodiodes based on compound semiconductors are established,the break-down characteristics and the linearity are studied.The simulated electric field distribution,carrier density,gain-bandwidth product and responsibility are extracted,which is used to explain the principle of the device and optimize the structure.The content is as following:(1)A model of 4H-SiC PIN ultraviolet avalanche photodiodes is established.The thickness and the doping concentration of the critical layer are changed to observe how the avalanche break-down voltage and the gain are affected.The results are explained by the electric field distribution and the width of the space-charge region.By fitting the extracted critical electric field strength from the simulation with the emprical formula from documents,the relation between the critical electric field strength of avalanche break-down and the doping concentration is concluded,providing a theoretical basis for optimization of the break-down voltage.(2)A model of InAlAsSb SACM(separate absorption,charge and multiplication)infrared avalanche photodiodes is established.The thickness and the doping concentration of the absorption layer,the charge layer and the multiplication layer are changed to observe how the avalanche break-down voltage,the punch-through voltage and the gain are affected.By altering the multiplication layer to a hetero-junction structure with high/low band-gap layers,the avalanche break-down voltage is decreased without raising the punch-through voltage.(3)A model of InGaAs/InAlAs SAGCM(separate absorption,grading,charge and multiplication)infrared avalanche photodiodes is established.By controlling the structure of the grading layer and the charge layer,the thickness and the doping concentration of the grading layer,the thickness of the absorption layer,the linearity is studied,as well as the break-down characteristic,gain and responsibility.