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Schematic diagram of the -QWIP (as-grown). Three doped layers (labeled TC, MC, and BC) separate two major active regions; one containing MWIR quantum wells (InGaAs) and the other containing LWIR quantum wells (GaAs). Three different measurement configurations (TM, MB, and TB) are also indicated.
The conduction band profile of the detector for negative bias (negative on TC). Under this condition, the band profile of the TM region is close to the flat-band situation, making the MWIR wells inactive for photocarrier generation. Hence, photocarrier generation takes place only in the LWIR wells, as indicated by vertical arrows. Similarly, the MWIR well becomes active for positive bias.
Dark current characteristics of the detector at (a) 300 K and (b) 77 K, measured across TM, MB, and TB. TM and MB regions separately show typical I-V characteristics of a structure as expected. Three out of four mesas on this sample show very similar I-V, indicating a good uniformity.
(a) Interband response of the -QWIP measured with front-side illumination. (b) Intersubband spectral response measured with 45° back-side illumination at 80 K for positive (left scale) and negative (right scale) bias voltages indicated by and V(−). A good selection between the MWIR and LWIR bands can be observed. When this detector is coupled with a grating, both interband and intersubband responses can be measured with normal incidence light.
Active elements in an -based -QWIP.
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