We examine carrier transport in unipolar barrier infrared photodetectors and discuss aspects of barrier, contact, and absorber properties that can affect minority carrier collection. In a barrier infrared detector the unipolar barrier should block only the majority carriers while allowing the un-impeded flow of the minority carriers. Under the right conditions, unipolar barrier doping can reduce generation-recombination dark current without affecting minority carrier extraction. In an nBn structure, ideally with an electron unipolar barrier, improper barrier doping or barrier-absorber valence band offset could also block minority carriers and result in higher turn-on bias. We also examined the temperature-dependent turn-on bias in an n⁺Bn device and showed that observed behavior may be attributed to contact doping. Hole mobility in n-doped type-II superlattice (T2SL) is believed to be very low because of the extremely large effective mass along the growth direction. In practice MWIR and LWIR barrier infrared detectors with n-type T2SL absorbers have demonstrated good optical response. A closer inspection of the T2SL band structure offers a possible explanation as to why the hole mobility may not be as poor as suggested by the simple effective mass picture.

Date Published: 4 June 2015
PDF: 8 pages
Proc. SPIE 9451, Infrared Technology and Applications XLI, 94510P (4 June 2015); doi: 10.1117/12.2177549

Published in SPIE Proceedings Vol. 9451:
Infrared Technology and Applications XLI
Bjørn F. Andresen; Gabor F. Fulop; Charles M. Hanson; Paul R. Norton, Editor(s)