Advanced Sensor Materials for Space

GaSb substrates have advantages that make them attractive for implementation of very long wavelength infrared (VLWIR) detectors with higher operating temperatures for stealth and space based applications. A significant processing issue for detector fabrication based upon InAs/GaSb and related strained layer superlattices (SLS) is the substrate transmissivity in the VLWIR range. In order to preclude substrate thinning for backside illuminated devices, a extremely low n-type substrate is desired. An opportunity exists to modify the Czochralski growth process to minimize the Ga antisite defect formation and significantly reduce the residual p-type carrier concentration. Using a modified melt stoichiometry, a faster liquid/solid interface rotation speed, and a slow cool ramp profile at the critical temperatures for vacancy formation/vacancy clustering, an extremely low doped n-GaSb boule may be fabricated. Hall Effect carrier concentration and FTIR transmissivity of substrates as a function of boule length will be examined. Deliverables for MBE SLS growth will be supplied to MDA and Raytheon. Phase II will incorporate a boule pull rate parameter and the establishment of a manufacturing process for larger diameter VLWIR suitable substrates. Commercialization of the GaSb substrate surface preparation process is regarded with high probability.