These detectors can be used in infrared imaging cameras in manufacturing process monitoring, environmental monitoring, and medical imaging.
The complementary barrier infrared detector (CBIRD) is designed to eliminate the major dark current sources in the superlattice infrared detector. The concept can also be applied to bulk semiconductor-based infrared detectors. CBIRD uses two different types of specially designed barriers: an electron barrier that blocks electrons but not holes, and a hole barrier that blocks holes but not electrons. The CBIRD structure consists of an n-contact, a hole barrier, an absorber, an electron barrier, and a p-contact.
The barriers are placed at the contact-absorber junctions where, in a conventional p-i-n detector structure, there normally are depletion regions that produce generation-recombination (G-R) dark currents due to Shockley-Read-Hall (SRH) processes. The wider-bandgap complementary barriers suppress G-R dark current. The barriers also block diffusion dark currents generated in the diffusion wings in the neutral regions. In addition, the wider gap barriers serve to reduce tunneling dark currents. In the case of a superlattice-based absorber, the superlattice itself can be designed to suppress dark currents due to Auger processes. At the same time, the barriers actually help to enhance the collection of photo-generated carriers by deflecting the photo-carriers that are diffusing in the “wrong” direction (i.e., away from collectors) and redirecting them toward the collecting contacts. The contact layers are made from materials with narrower bandgaps than the barriers. This allows good ohmic contacts to be made, resulting in lower contact resistances.
Previously, THALES Research and Technology (France) demonstrated detectors with bulk InAsSb (specifically InAs0.91Sb0.09) absorber lattice-matched to GaSb substrates. The absorber is surrounded by two wider bandgap layers designed to minimize impedance to photocurrent flow. The wide bandgap materials also serve as contacts. The cutoff wavelength of the InAsSb absorber is fixed. CBIRD may be considered as a modified version of the THALES double heterostructure (DH) p-i-n device, but with even wider bandgap barriers inserted at the contact layer/absorber layer interfaces. It is designed to work with either bulk semiconductors or superlattices as the absorber material. The superlattice bandgap can be adjusted to match the desired absorption cutoff wavelength.
This infrared detector has the potential of high-sensitivity operation at higher operating temperatures. This would reduce cooling requirements, thereby reducing the power, mass, and volume of the equipment and allowing an increased mission science return.
This work was done by David Z. Ting, Sumith V. Bandara, Cory J. Hill, and Sarath D. Gunapala of Caltech for NASA’s Jet Propulsion Laboratory.
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