9629636 Campbell The objectives of this research program will be two fold: 1) to build on previous work in the avalanche photodiodes (APD) photodetectors to develop a realistic model that can be used as a tool to facilitate device design and optimization and to conduct a systematic experimental study of the critical structural parameters, including the bandedge discontinuities, the widths of the barrier and well regions, and the composition profile of the barrier layers. Tight coupling between the simulation and experimental work is a strength of this program and will provide the feedback necessary for understanding and developing these technologically important photodetectors. 2) It is also the objective of this proposed research to realize new photodetectors that utilize novel resonantcavity structures to achieve enhanced performance relative to conventional photodetectors. A crucial aspect to achieving these novel photodetectors is a fundamental understanding of the physical effects that determine their performance. For example, the resonantcavity approach has been successfully extended to avalanche photodiodes. However, there are aspects to the impact ionization process in this type of structure that are not well understood. The resonant-cavity structure can provide several performance advantages, one of which is that the tradeoff between responsivity/bandwidth that is inherent to conventional PIN photodiodes structures can be circumvented. For the typical normal-incidence photodetector, a wide bandwidth necessitates a thin absorption layer which, in turn, results in low quantum efficiency. The resonant-cavity structure, on the other hand, effectively decouples the responsivity from the transit-time component of the bandwidth because the optical signal makes multiple passes across the thin absorbing layer inside the microcavity. For example, it has been demonstrated with Si-based resonant-cavity photodiodes that a 10x increase in bandwidth can be achieve without sacrificing quantum efficiency. In addition, the narrow spectral response of these photodetectors may be used to advantage for applications such as wavelength-division multiplexing. For example, high Q cavities can provide an integrated filtering function. ***
