Dark current optimization with band gap engineering has been numerically studied for InGaAs nBn type infrared photodetectors. Undoped InAlGaAs grading layers are utilized in constructing the barrier and dipole deltadoped layers are placed in both sides of the graded layers for eliminating valence band offset. As a result, the high band gap barrier layer blocks the majority carriers and allows minority carrier flow while minimizing various dark current components, as expected from an nBn

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... . Substantial improvement has been shown in the dark current level without compromising any photoresponse compared to the conventional pn junction and recently proposed all InGaAs nBn type photodetectors.