1.1 - InAS/GaSb Superlattices for High-Performance Infrared Detection

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings IRS² 2011
I1 - Photon and Thermal Detectors
F. Rutz, R. Rehm, J. Schmitz, M. Wauro, J. Niemasz, J. Masur, A. Wörl, M. Walther - Fraunhofer-Institute for Applied Solid State Physics (IAF), Freiburg (Germany), R. Scheibner, J. Wendler, J. Ziegler - AIM Infrarot-Module GmbH, Heilbronn (Germany)
16 - 20


Photodiodes based on InAs/GaSb short-period superlattices (SLs) have proven their great potential for high-performance infrared (IR) detectors. These heterostructures are characterized by a broken band gap type-II band alignment leading to spatially indirect transitions between hole states localized in the GaSb layers and delocalized electronic states in the InAs layers. A high effective electron mass results in low tunneling currents and a low Auger recombination rate compared to CdHgTe detectors. The quantum efficiency of InAs/GaSb SLs is comparable to CdHgTe and allows short integration times and high camera frame rates, respectively. Furthermore, the effective band gap of these structures can be tailored in the range between 3 – 30 μm and depends directly on the layer thickness rather than on the stoichiometry as in the CdHgTe material system. The detector structures are grown by molecular beam epitaxy on commercial 3” GaSb substrates with low defect density. A well established process technology is used o fabricate focal plane arrays with high pixel yield without large cluster defects and a homogeneous and stable performance. The detector chips are hybridized with a customdesigned silicon readout integrated circuit using flipchip indium solder bump technology. These detector hybrids are mounted into a detector cooler assembly with a linear Stirling cooler, which is part of a complete IR imaging camera system.

Beside monospectral mid-wavelength IR (3 – 5 μm) camera systems, exhibiting an excellent noise equivalent temperature difference (NETD) below 10 mK with F/2.0 optics, Fraunhofer IAF and AIM currently develop the third generation of high-performance IR imaging systems, offering enhanced functionality, i.e. larger spatial resolution and/or multi-spectral detection within two separate bands (“dual-band”) or within the same spectral band (“dual-color”). A bispectral 288x384 dual-color InAs/GaSb SL camera system with cutoff wavelengths around 4 μm and 5 μm, respectively, allows simultaneous detection of two different spectral bands on the same pixel. Via a spatially and temporally coherent detection of two different wavelength ranges in the MWIR, the dualcolor SL imagers enable fast and highly sensitive remote detection of carbon dioxide. Applications range from missile warning for airborne platforms to remote detection of gas leakages. Recently, NETD values of 22 mK have been measured for the short wavelength det ector and 11 mK for the long wavelength detector with F/2.0 optics and 1.5 ms integration time.