The evolution of long-haul optical fiber telecommunications systems to bit rates greater than 10 GB/s has created a need for avalanche photodiodes (APDs) with higher bandwidths and higher gain-bandwidth products than are currently available. It is also desirable to maintain good quantum efficiency and low excess noise. At present, the best performance (f3dB ~ 15 GHz at low gain and gain-bandwidth product ~ 150 GHz) has been achieved by AlInAs/InGaAs(P) multiple quantum well (MQW) APDs. In this paper we report a resonant-cavity InAlAs/InGaAs APD that operates near 1.55 μm. These APDs have achieved very low noise (k equivalent to 0.18) as a result of the very thin multiplication regions that were utilized. The low noise is explained in terms of a new model that accounts for the non-local nature of impact ionization. A unity-gain bandwith of 24 GHz and a gain-bandwidth-product of 290 GHz were achieved.
