Optimization of Multiplication Factor of Avalanche Photodiode

General formulas for the photomultiplication factor M p are derived by considering the dark current injected into the avalanche region and the space charge effect due to the avalanche current. The numerical calculations were carried out in case of the silicon PN junction. The optimum impurity concentration to maximize M p in the avalanche region is derived for a given junction area and a given load resistance. The analyses also indicate M p is much improved with decreasing the dark current. The analytical results are well confirmed in the silicon P + PNN + diode with an engraved guard ring. The junction uniformity was improved by gallium diffusion ( P) preceding boron diffusion ( P + ). Both the spatial variation of M p in the junction plane and the avalanche noise were reduced to one tenth of those of the conventional P + N junction diodes.