Industrialization of type-II superlattice infrared detector technology at Fraunhofer IAF

Type-II superlattices (T2SLs) are considered the III/V alternative to HgCdTe for infrared (IR) detectors and have already reached market maturity. Fraunhofer IAF has demonstrated mono- and bi-spectral T2SL focal plane arrays up to 640×512 pixels for mid- and long-wavelength IR. In order to develop an industry-compatible T2SL technology, we have established the complete chain for detector array fabrication including design and modelling, epitaxial growth, as well as front- and backside processing. The epitaxial growth of T2SLs is performed by molecular beam epitaxy (MBE) in multi-wafer reactors. In this paper, we report on the control of growth rates during epitaxy, uniformity and reproducibility of the growth process, as well as characterization techniques to monitor the quality of the epitaxial layers. For the superlattice period, an average thickness variation far below a single atomic monolayer is required and achieved routinely. The standard deviation of the photoluminescence peak for both colors of bi-spectral IR detectors is around 0.04 μm for consecutive growth runs. With this very stable and reproducible epitaxial growth process in conjunction with our mature front- and backside processing we have been able to set up a pilot line production for bi-spectral T2SL IR detector arrays.