Resonant microcavity photodetectors

Photodetectors with both high bandwidth and high quantum efficiencies are crucial components for a variety of key technologies such as telecommunications, information processing, storage and sensing. The most widely used devices today are p.. i-n photodetectors and avalanche photodetectors. However, conventional device structures suffer from inherent bandwidth- quantum efficiency tradeoff. It can be shown that for small values of absorption layer thickness d, the RC limited bandwidth, which is a function of the active area diameter and d, can be the determining factor governing the frequency response of the device. For the same absorption coefficient, but for higher vales of d, i.e. wider absorption regions, the transit-timelimited bandwidth governs the frequency response. This is due to the fact that for a wider absorption region, the photogenerated carriers have a longer path to travel in order to reach their respective contacts. Thus it would seem beneficial to design structures with thin absorption regions. This would however, limit the quantum efficiency of the device, as is evident from Fig. 1. Most llIV semiconductors of interest have absorption coefficients of approximately, 10' cm, for the wavelengths of interest for telecommunications. Thus, in order to have a quantum efficiency of approximately 80 %, a minimum absorption region thickness of 2 xm is required.