Modeling Tools For Design Of Type-II Superlattice Photodetectors

Type-II superlattice detectors for infrared imaging in the MWIR and LWIR bands have attracted considerable interest over the past decade from academia, as well as from commercial enterprises. These detectors often employ clever bandgap engineering, such as unipolar barriers, which only block majority carriers, and elaborate doping schemes in order to minimize dark current generation. The fact that the entire detector material is grown by molecular beam epitaxy limits the total thickness of the detector structure. The absorption and photo current generation consequently takes place in a relatively thin region, compared to competing technologies, such as InSb and MCT. Design of an optical cavity in relation to the wavelength range of interest might therefore be needed to increase the quantum efficiency.
We present a wide range of modeling tools that are used in the design and performance evaluation of type-II superlattice detectors. Among these are
• A k.P band structure modeling tool for the superlattice period design;
• A dark current vs. bias fitting/analysis tool;
• An optical and photo carrier transport model for the spectral total external QE, which takes into account carrier diffusion length;
• An electrical device model for band bending, charge accumulation, doping optimization etc.;
• Focal plane array (FPA) performance modeling tools for the prediction and evaluation of final device performance after hybridization to appropriate read-out integrated circuitry.
The modeling tools are discussed and examples of their use are given for MWIR and LWIR type-II detectors based on InAs/AlSb/GaSb superlattices.