DELTA-DOPED AVALANCHE PHOTODIODES FOR HIGH BIT-RATE LIGHTWAVE RECEIVERS

High-performance photodetectors are an essential component of future fiber-optic based communication systems operating at multigigabit-per-second bit rates. Separate absorption, grading, and multiplication avalanche photodiodes (SAGM-APD's) have attained gain-bandwidth products of over 85 GHz. Due to various design constraints stemming from intrinsic material properties, chief among them being the maximum doping limit for the InP multiplication layer, higher gain-bandwidth (GB) products in this structure have not yet been achieved. In this paper, we estimate the GB product limits and the noise performance of a new SAGM-APD structure: the delta-doped SAGM-APD. We show that GB products in excess of 140 GHz for a 0.2-mu-m-thick multiplication layer and possibly larger GB products for smaller widths can be obtained. While recent calculations have predicted increased GB products for this delta-doped SAGM-APD structure, in this paper, we explicitly prove using conventional theory that this is possible only with a concomitant increase in the multiplication noise. We further demonstrate 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. Finally, we shown that the delta-doped SAGM-APD structure is a very good candidate for high bit-rate receiver applications.