An indirect method of studying band alignments in nBn photodetectors using off-axis electron holography

Mid-wave and long-wave infrared nBn photodetectors with absorbers consisting of InAs/InAsSb superlattices and barriers consisting of InAs/AlGaSb(As) superlattices were grown using molecular beam epitaxy. High-resolution X-ray diffraction showing significant differences in Ga composition in the barrier layer, and different dark current behavior at 77 K, suggested the possibility of different types of band alignments between the barrier layer and the absorber for the mid- and long-wave infrared samples. Examination of the barrier layers using off-axis electron holography showed the presence of positive charge with an estimated density of 1.8 × 10¹⁷/cm³ in the mid-wave sample as a result of a type-II band alignment, whereas negligible charge was detected in the long-wave sample, consistent with a type-I band alignment.