In this paper, we present an nBn type dual-band InGaAs photodetector design with bias selectable cut-off wavelengths of 1.7 μm and 2.5 μm. InP based epilayer design consists of a compositionally graded quaternery InAlGaAs barrier region sandwiched between lattice matched InGaAs absorber and extended InGaAs absorber. In this study, we also provide a comparison between suggested nBn structure and a relatively usual npn InGaAs structure, using the same computational environment.
Low dark current and/or high operating temperature are the main motivations behind the nBn detector structures where removing the valence band discontinuity is usually an important design challenge. With the utilization of the bias polarity, these structures can also be easily designed as dual-band detectors and in this study, a dual-band (MWIR / LWIR) HgCdTe nBn detector configuration has been numerically examined. Valence band barrier suppression has been obtained with the delta-doped and compositional graded layers similar to the recent single band studies.
It is numerically shown that Al/Sb free InGaAs unipolar barrier detectors with superior performance compared to the conventional heterojunction detectors can be constructed. Compositionally graded layers provide the transition between the high bandgap InGaAs barrier and the lattice matched InGaAs absorber layers. In addition, the delta doped layers remove the valence band offset in order to block only majority carriers and allow unimpeded flow of minority carriers. More than one order of magnitude reduction in the dark current is observed while photocurrent remains nearly unchanged. Proposed barrier structure utilized in this study is not limited to short wave infrared (SWIR) and can be applied to a variety of materials operating in various infrared regions.
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