Delta-doped avalanche photodiodes for high bit-rate lightwave receivers

The authors estimate the GB (grain bandwidth) product limits and the noise performance of a new SAGM-APD (separate avalanche, grating, and multiplication avalanche photodiode) structure: the δ-doped SAGM-APD. It is shown that GB products in excess of 140 GHz for a 0.2-μm-thick multiplication layer and possibly larger GB products for smaller widths can be obtained. While recent calculations have predicted increased GB products for this δ-doped SAGM-APD structure, the authors explicitly prove using conventional theory that this is possible only with a concomitant increase in the multiplication noise. It is further demonstrated that it is essential to optimize the width of the multiplication layer for a given bit-rate to achieve minimum multiplication noise consistent with a GB product high enough to accommodate the requisite frequency response at the optimum gain. It is shown that the δ-doped SAGM-APD structure is a very good candidate for high bit-rate receiver applications