|
Much progress has been made in the past 2 years in developing III-V antimonide-based superlattice infrared detectors
and focal plane arrays (FPAs). In the area of detector material growth by molecular beam epitaxy, the wafer foundry
group, helped by government-trusted entities and other partnering institutions, has leapfrogged many years of R&D
effort to become the premier detector wafer supplier. The wafers produced are of high quality as measured by surface
morphology, defect density, photoluminescence property, high-resolution X-ray diffraction, and diode current-voltage
characteristics. In the area of detector design and FPA processing, the team-consisting of members from government
laboratories, academia, and the FPA industry-has made rapid progress in device structure design, detector array
etching, passivation, hybridization, and packaging. The progress is reflected in the steady reduction in FPA median darkcurrent
density and improvement in median quantum efficiency, as well as reasonably low median noise-equivalent
different temperature under 300 K scene background, when compared with the performance from some of the
commercially available HgCdTe FPAs. In parallel with the FPA research and development effort, a small amount of
funding has been devoted to measuring minority carrier lifetimes and to understanding life-killing defects and
mechanisms of superlattice devices. Results of direct time-resolved photoluminescence measurement on superlattice
absorbers indicate relatively short lifetimes (on the order of 30 ns) due to Shockley-Read-Hall mechanism. Modeling and
curve fitting with diode current-voltage data indicate longer minority carrier lifetimes, although the best fit lifetime
values differ greatly, possibly due to the difference in material quality and device structure. Several models or
hypotheses have been proposed to explain experimental data. More data are required to validate these models and
hypotheses. Further work is also necessary to reconcile the substantially different results from different groups and to
truly understand the physics of minority carrier lifetimes, which is necessary to improve the lifetime and realize the
theoretical promise of superlattice materials.
|
