Dr J S Marsland
In the past the usefulness of avalanche photodiodes has been limited by the additional noise produced by the avalanche mechanism. New theoretical work performed in the Solid State group has shown how an avalanche photodiode may be modified to limit the additional noise. Figure 1 shows that the excess noise factor is reduced to nearly one, the value expected for a completely noise free avalanche, for gains of 2, 4, 8 and 16. The five lines relate to five different values of the ionization coefficient ratio, k, and the dotted lines show the excess noise factor for the same k values predicted by established theory that does not include the non-local nature of impact ionization. Research opportunities exist in this area in both further theoretical study and in experimental measurement of device performance.
Figure 1 - Excess noise factor