Heterojunction photodiode

See also Field effect transistors (FETs) Heterojunction insulated gate FETs (HIGFETs), 22 164. See also Field effect transistors (FETs) Heterojunction photodiode arrays,... 

Conjugated Polymer/Conjugated Polymer Bulk Heterojunction Photodiodes... 

The second photon effect of general utility is the photovoltaic effect. Unlike the photoconductive effect, it requires an internal potential barrier with a built-in electric field to separate a photoexcited hole-electron pair. Although it is possible to have an extrinsic photovoltaic effect, see Ryvkin [2.32], almost all practical photovoltaic detectors employ the intrinsic photoeffect. Usually this occurs at a simple p — n junction. However, other structures employed include those of an avalanche, p—i — n, Schottky barrier and heterojunction photodiode. There is also a photovoltaic effect occuring in the bulk. Each will be discussed, with emphasis on the p—n junction photoeffect. 

The above discussion has been confined to the photovoltaic effect arising at a p—n junction in a semiconductor due to photoexcitation of carriers on either side of the junction. Among the related areas of interest are a) avalanche photodiodes, b) p—i—n photodiodes, c) Schottky barrier photodiodes, d) heterojunction photodiodes, and e) bulk photovoltaic effect Each of these will be discussed briefly. 

Heterojunction Photodiode. In the early 1960s there was considerable interest in semiconductor heterojunctions for use as wide gap emitters in transistors. The heterojunctions were formed by epitaxial growth of one semiconductor, e.g. GaAs, on another, e.g. Ge, having a similar lattice structure and periodicity. Rectification properties could be observed not only in the p—n junction configuration but also in n—n and p — p configurations. The reasons for this were detailed by Anderson [2.44]. 

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