An epitaxial photoconductive detector for high speed optical detection

In previous work (1,2,3,4) it has been shown that the OPFET is capable of high speed optical detection. Advantages of this detector are: internal gain, low voltage operation, high speed and low noise. The OPFET suffers the disadvantage of small active area which makes it difficult to apply for efficient detection of signals from multimode fibers. A new type of photoconductive detector is described in this paper that has active area comparable to that of a PIN photodiode. A n⁺, p^-, n⁺structure is used under bias conditions similar to a punched-through transistor. The injecting boundary conditions cause the p-epitaxial layer to behave as a photoconductor, thus providing high speed photoconductive gain. This internal detector gain is important in applications where the noise of the external electronics dominates. The advantage of this detector over the avalanche photodiode is that only low voltage is required. The detector is also expected to have low noise and may be competitive in this respect.