SBIR-STTR Award

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.

Keywords:
Gasb Substrate Growth, Vlwir Transmissivity, Sls Fabrication, Spaced-Based Detector, Extremely Low N-Type Gasb, Ga Antisite Defect Supression, Vlwir Detectors, Gasb Boule

Advanced technology and circuit architecture is under investigation for high performance, infra-red, and low power electronics. GaSb substrates have advantages that are attractive for implementation of very long wavelength infrared (VLWIR) detectors with higher operating temperatures for spaced based and stealth applications. A significant aspect inhibiting widespread commercial application of GaSb wafers for VLWIR is the lack of transparency beyond 15ƒ?m. Due to antisite and other point defects in undoped GaSb substrates, intrinsic GaSb is still slightly p-type which strongly absorbs VLWIR wavelengths. Even for low n-type GaSb substrates, the substrate requires backside thinning for IR transparency. In Phase I, ultra-low n-type GaSb substrates (n<4x1015/cm3) were fabricated. For the first time, GaSb VLWIR transparency was exhibited to 25ƒ?m with 35X improvement in %transmittance. Elimination of backside thinning for VLWIR devices should be enabled. A Phase II manufacturing process for ultra-low n:GaSb will be established. Melt-interface thermodynamics established in Phase I will be optimized. Theoretical boule cooling ramp rates will be further engineered with an encapsulating jacket. Strained-layer-superlattice (SLS) and VLWIR device processing will be implemented in conjunction with Lockheed-Martin, Raytheon, and Teledyne Scientific. Phase III commercialization probability for ultra-low doped n:GaSb is high, with established customers expressing commitment.

Keywords:
Type-Ii Sls, Vlwir, Iii-V, Ir Detector, Gasb, T2sls, Multiband, Strained Layer Superlattice