Type II superlattice photodetectors for MWIR to VLWIR focal plane arrays

Infrared sensors utilizing Type 11 superlattice structures have gained increased attention in the past few years. With the stronger covalent bonds of the Ill-V materials, greater material uniformity over larger areas is obtained as compared to the weaker ionic bonding of the II-VI materials. Results obtained on GaSb/InAs Type 11 superlattices have shown performance comparable to HgCdTe detectors, with the promise of higher performance due to reduced Auger recombination and dark current through improvements in device design and material quality. In this paper, we discuss advancements in Type 11 IR sensors that cover the 3 to > 30 pm wavelength range. Specific topics covered will be device design and modeling using the Empirical Tight Binding Method (ETBM), material growth and characterization, device fabrication and testing, as well as focal plane array processing and imaging. We demonstrate high quality material with PL linewidths of similar to 20 meV, x-ray FWHM of 20-40 arcsec, and AFM rms roughness of similar to 1.2 angstrom over a 20 mu m x 20 mu m area. Negative luminescence at 10 mu m range is demonstrated for the first time. Device external quantum efficiency of > 30%, responsivity of similar to 2A/W, and detectivity of 10(11) Jones at 77K in the 10 mu m range are routinely obtained. Imaging has been demonstrated at room temperature for the first time with a 5 gm cutoff wavelength 256x256 focal plane array.