Superlattice Materials for Very-Long Wavelength Infrared Detectors (VLWIR)

"The fabrication of large format, highly sensitive Focal Plane Arrays (FPAs), sensing at very long wavelength in the IR region i.e beyond 15um (VLWIR) is highly desirable for Air Force's space based applications. Currently, only limited types of arrays suchas 256 X 256 Si:As (5-20 um) are available in this IR region. However, these extrinsic detectors suffer from some fundamental limitations, such as low quantum efficiency, relatively low detection sensitivity and low operating temperature. Intrinsicdetectors made from HgTe/CdTe superlattices (SLs) have several advantages over extrinsic detectors such as low tunneling current, low noise and high quantum efficiencies. Compared to bulk HgCdTe, the cut-off wavelength of HgTe/CdTe SLs can be easily tunedto VLWIR by adjusting the layer thickness of HgTe layers. Strained layer HgTe/CdZnTe SLs can even be band structure engineered in order to suppress Auger recombination and impact ionization, which will lead to lower noise and higher operating temperature.Another important advantage of HgTe/CdTe SLs, compared to HgCdTe, is related to the p-type doping which can be achieved without high temperature annealing through arsenic incorporation in CdTe layers. Furthermore these SLs could be grown on Si substrateswhich would pave the way for Megapixel hybrid or possibly monolithic VLWIR FPAs/ Through the design of HgTe/CdTe SL's electronic band structure, detectivity computation and in-situ control