Type II superlattice photodetectors for MWIR to VLWIR focal plane arrays

Infrared sensors utilizing Type II superlattice structures have gained increased attention in the past few years. With the stronger covalent bonds of the III-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 II 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 II IR sensors that cover the 3 to >30 μm 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 ~20 meV, x-ray FWHM of 20-40 arcsec, and AFM rms roughness of 1~.2 Å over a 20 μm×20μm area. Negative luminescence at 10 μm range is demonstrated for the first time. Device external quantum efficiency of >30%, responsivity of ~2A/W, and detectivity of 1011 Jones at 77K in the 10 μm range are routinely obtained. Imaging has been demonstrated at room temperature for the first time with a 5 μm cutoff wavelength 256×256 focal plane array.