Type-II superlattices: a promising material for space applications

Abstract

Type-II superlattices (T2SLs) are currently recognized as the sole material system offering comparable performance to HgCdTe, yet providing higher operability, stability over time, spatial uniformity, scalability to larger formats, producibility and affordability. Hence, T2SL technology is very promising for space applications. Fraunhofer IAF played a vital role in the development of III-As/Sb T2SLs right from the beginning. Mono-and bi-spectral focal plane arrays up to 640×512 pixels for the mid-and long-wavelength infrared (IR) have been demonstrated. The growth of T2SL is performed by molecular beam epitaxy (MBE) in multi-wafer reactors. We report on the excellent homogeneity and reproducibility of the growth process, established in the past years at Fraunhofer IAF. After processing this material to detector arrays, the T2SL detectors have been characterized down to low temperatures (below 40K) with promising properties regarding the dark current. For MWIR and LWIR detectors the resolution limit of the measurement setup with a dark current density of 2×10 -10 A/cm² has been reached at 77 K and 36 K, respectively.