Study of the frequency response of the multiplication gain of a two-layer avalanche photodiode

A study of the multiplication gain against frequency has been made for a two-layer avalanche photodiode consisting of an avalanche layer and a drift layer. The analysis shows that as the ratio of the avalanche-layer width to drift-layer width increases (keeping the total depletion-layer width fixed), the multiplication gain increases but the bandwidth of the diode decreases. However, when photons are absorbed in the p-region, i.e., before entering the depletion region, the multiplication gain of the diode remains almost the same while the bandwidth increases as the structure changes from p-i-n to Read type.