InAs/(GaIn)Sb short-period superlattices for focal plane arrays

on the mesa sidewalls. Some larger diodes show significantly higher (R0A) -1 values which are attributed to growth
defects in the bulk of the diode. This interpretation is in accordance with the histogram of 12 quadratic diodes with 70
µm edge length (P/A = 0.057 µm -1 ) from Figure 10a, which is shown in Figure 10b. Only one diode (#11) out of 12
randomly selected diodes differs significantly from R0A ≈ 5 – 10 Ωcm 2 . Further experimental investigations, which are
beyond the scope of this paper, do not suggest any problems with the long-term stability or reproducibility of the
Al0.5Ga0.5As0.04Sb0.96 passivation.
4. CONCLUSIONS
Important progress on short-period p-i-n superlattice photodiodes based on the InAs/GaInSb material system could be
achieved in both atmospheric transmission windows in the infrared spectral range. In the 3-5 µm regime the first fully
operational 256x256 camera system was demonstrated exhibiting a NETD performance of 9.4 mK at 6.5 ms integration
time with F/2 optics at 73 K. The excellent homogeneity of the electro-optical performance combined with the very low
pixel outages without any large cluster defects constitute an important advantage over state-of-the-art HgCdTe detectors
at comparable performance. In the 8-10 µm region a method based on the epitaxial MBE overgrowth with high bandgap
AlGaAsSb offers a stable method to passivate InAs/GaInSb superlattice photodiodes. No surface leakage currents were
observed in test diodes as small as 70 µm diameter. Since the illustrated approach is compatible with standard device
processing, the realization of the first superlattice FPA in the 8-10 µm window seems within reach.
ACKOWLEDGMENTS
The authors are grateful to K. Schwarz, H. Güllich, L. Kirste and K. Windscheid for characterization of detector
structures. We also express our thanks to P. Koidl and G. Weimann for fruitful discussions. Financing support by the
Federal Ministry of Defense is gratefully acknowledged.
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